Commit graph

393 commits

Author SHA1 Message Date
Linus Torvalds
5943026240 vfs: fix race in rcu lookup of pruned dentry
Don't update *inode in __follow_mount_rcu() until we'd verified that
there is mountpoint there.  Kudos to Hugh Dickins for catching that
one in the first place and eventually figuring out the solution (and
catching a braino in the earlier version of patch).

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-07-19 21:49:01 -07:00
Al Viro
94c0d4ecbe Fix ->d_lock locking order in unlazy_walk()
Make sure that child is still a child of parent before nested locking
of child->d_lock in unlazy_walk(); otherwise we are risking a violation
of locking order and deadlocks.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-07-12 21:40:23 -04:00
Al Viro
8e833fd2e1 fix comment in generic_permission()
CAP_DAC_OVERRIDE is enough for MAY_EXEC on directory, even if
no exec bits are set.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-06-20 10:45:56 -04:00
Al Viro
6291176bcd kill obsolete comment for follow_down()
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-06-20 10:45:49 -04:00
Al Viro
8aef188452 VFS: Fix vfsmount overput on simultaneous automount
[Kudos to dhowells for tracking that crap down]

If two processes attempt to cause automounting on the same mountpoint at the
same time, the vfsmount holding the mountpoint will be left with one too few
references on it, causing a BUG when the kernel tries to clean up.

The problem is that lock_mount() drops the caller's reference to the
mountpoint's vfsmount in the case where it finds something already mounted on
the mountpoint as it transits to the mounted filesystem and replaces path->mnt
with the new mountpoint vfsmount.

During a pathwalk, however, we don't take a reference on the vfsmount if it is
the same as the one in the nameidata struct, but do_add_mount() doesn't know
this.

The fix is to make sure we have a ref on the vfsmount of the mountpoint before
calling do_add_mount().  However, if lock_mount() doesn't transit, we're then
left with an extra ref on the mountpoint vfsmount which needs releasing.
We can handle that in follow_managed() by not making assumptions about what
we can and what we cannot get from lookup_mnt() as the current code does.

The callers of follow_managed() expect that reference to path->mnt will be
grabbed iff path->mnt has been changed.  follow_managed() and follow_automount()
keep track of whether such reference has been grabbed and assume that it'll
happen in those and only those cases that'll have us return with changed
path->mnt.  That assumption is almost correct - it breaks in case of
racing automounts and in even harder to hit race between following a mountpoint
and a couple of mount --move.  The thing is, we don't need to make that
assumption at all - after the end of loop in follow_manage() we can check
if path->mnt has ended up unchanged and do mntput() if needed.

The BUG can be reproduced with the following test program:

	#include <stdio.h>
	#include <sys/types.h>
	#include <sys/stat.h>
	#include <unistd.h>
	#include <sys/wait.h>
	int main(int argc, char **argv)
	{
		int pid, ws;
		struct stat buf;
		pid = fork();
		stat(argv[1], &buf);
		if (pid > 0) wait(&ws);
		return 0;
	}

and the following procedure:

 (1) Mount an NFS volume that on the server has something else mounted on a
     subdirectory.  For instance, I can mount / from my server:

	mount warthog:/ /mnt -t nfs4 -r

     On the server /data has another filesystem mounted on it, so NFS will see
     a change in FSID as it walks down the path, and will mark /mnt/data as
     being a mountpoint.  This will cause the automount code to be triggered.

     !!! Do not look inside the mounted fs at this point !!!

 (2) Run the above program on a file within the submount to generate two
     simultaneous automount requests:

	/tmp/forkstat /mnt/data/testfile

 (3) Unmount the automounted submount:

	umount /mnt/data

 (4) Unmount the original mount:

	umount /mnt

     At this point the kernel should throw a BUG with something like the
     following:

	BUG: Dentry ffff880032e3c5c0{i=2,n=} still in use (1) [unmount of nfs4 0:12]

Note that the bug appears on the root dentry of the original mount, not the
mountpoint and not the submount because sys_umount() hasn't got to its final
mntput_no_expire() yet, but this isn't so obvious from the call trace:

 [<ffffffff8117cd82>] shrink_dcache_for_umount+0x69/0x82
 [<ffffffff8116160e>] generic_shutdown_super+0x37/0x15b
 [<ffffffffa00fae56>] ? nfs_super_return_all_delegations+0x2e/0x1b1 [nfs]
 [<ffffffff811617f3>] kill_anon_super+0x1d/0x7e
 [<ffffffffa00d0be1>] nfs4_kill_super+0x60/0xb6 [nfs]
 [<ffffffff81161c17>] deactivate_locked_super+0x34/0x83
 [<ffffffff811629ff>] deactivate_super+0x6f/0x7b
 [<ffffffff81186261>] mntput_no_expire+0x18d/0x199
 [<ffffffff811862a8>] mntput+0x3b/0x44
 [<ffffffff81186d87>] release_mounts+0xa2/0xbf
 [<ffffffff811876af>] sys_umount+0x47a/0x4ba
 [<ffffffff8109e1ca>] ? trace_hardirqs_on_caller+0x1fd/0x22f
 [<ffffffff816ea86b>] system_call_fastpath+0x16/0x1b

as do_umount() is inlined.  However, you can see release_mounts() in there.

Note also that it may be necessary to have multiple CPU cores to be able to
trigger this bug.

Tested-by: Jeff Layton <jlayton@redhat.com>
Tested-by: Ian Kent <raven@themaw.net>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-06-16 11:28:16 -04:00
Török Edwin
50338b889d fix wrong iput on d_inode introduced by e6bc45d65d
Git bisection shows that commit e6bc45d65d causes
BUG_ONs under high I/O load:

kernel BUG at fs/inode.c:1368!
[ 2862.501007] Call Trace:
[ 2862.501007]  [<ffffffff811691d8>] d_kill+0xf8/0x140
[ 2862.501007]  [<ffffffff81169c19>] dput+0xc9/0x190
[ 2862.501007]  [<ffffffff8115577f>] fput+0x15f/0x210
[ 2862.501007]  [<ffffffff81152171>] filp_close+0x61/0x90
[ 2862.501007]  [<ffffffff81152251>] sys_close+0xb1/0x110
[ 2862.501007]  [<ffffffff814c14fb>] system_call_fastpath+0x16/0x1b

A reliable way to reproduce this bug is:
Login to KDE, run 'rsnapshot sync', and apt-get install openjdk-6-jdk,
and apt-get remove openjdk-6-jdk.

The buggy part of the patch is this:
	struct inode *inode = NULL;
.....
-               if (nd.last.name[nd.last.len])
-                       goto slashes;
                inode = dentry->d_inode;
-               if (inode)
-                       ihold(inode);
+               if (nd.last.name[nd.last.len] || !inode)
+                       goto slashes;
+               ihold(inode)
...
	if (inode)
		iput(inode);	/* truncate the inode here */

If nd.last.name[nd.last.len] is nonzero (and thus goto slashes branch is taken),
and dentry->d_inode is non-NULL, then this code now does an additional iput on
the inode, which is wrong.

Fix this by only setting the inode variable if nd.last.name[nd.last.len] is 0.

Reference: https://lkml.org/lkml/2011/6/15/50
Reported-by: Norbert Preining <preining@logic.at>
Reported-by: Török Edwin <edwintorok@gmail.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Török Edwin <edwintorok@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-06-16 11:27:39 -04:00
Theodore Ts'o
e6bc45d65d vfs: make unlink() and rmdir() return ENOENT in preference to EROFS
If user space attempts to remove a non-existent file or directory, and
the file system is mounted read-only, return ENOENT instead of EROFS.
Either error code is arguably valid/correct, but ENOENT is a more
specific error message.

Reported-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-06-07 08:51:14 -04:00
Sage Weil
3cebde2413 vfs: shrink_dcache_parent before rmdir, dir rename
The dentry_unhash push-down series missed that shink_dcache_parent needs to
be called prior to rmdir or dir rename to clear DCACHE_REFERENCED and
allow efficient dentry reclaim.

Reported-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-05-30 01:48:27 -04:00
Al Viro
d6e9bd256c Lift the check for automount points into do_lookup()
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-05-27 07:03:15 -04:00
Al Viro
dea3937619 Trim excessive arguments of follow_mount_rcu()
... and kill a useless local variable in follow_dotdot_rcu(), while
we are at it - follow_mount_rcu(nd, path, inode) *always* assigned
value to *inode, and always it had been path->dentry->d_inode (aka
nd->path.dentry->d_inode, since it always got &nd->path as the second
argument).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-05-27 07:01:49 -04:00
Al Viro
287548e46a split __follow_mount_rcu() into normal and .. cases
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-05-27 06:51:56 -04:00
Linus Torvalds
32e51f141f Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6: (25 commits)
  cifs: remove unnecessary dentry_unhash on rmdir/rename_dir
  ocfs2: remove unnecessary dentry_unhash on rmdir/rename_dir
  exofs: remove unnecessary dentry_unhash on rmdir/rename_dir
  nfs: remove unnecessary dentry_unhash on rmdir/rename_dir
  ext2: remove unnecessary dentry_unhash on rmdir/rename_dir
  ext3: remove unnecessary dentry_unhash on rmdir/rename_dir
  ext4: remove unnecessary dentry_unhash on rmdir/rename_dir
  btrfs: remove unnecessary dentry_unhash in rmdir/rename_dir
  ceph: remove unnecessary dentry_unhash calls
  vfs: clean up vfs_rename_other
  vfs: clean up vfs_rename_dir
  vfs: clean up vfs_rmdir
  vfs: fix vfs_rename_dir for FS_RENAME_DOES_D_MOVE filesystems
  libfs: drop unneeded dentry_unhash
  vfs: update dentry_unhash() comment
  vfs: push dentry_unhash on rename_dir into file systems
  vfs: push dentry_unhash on rmdir into file systems
  vfs: remove dget() from dentry_unhash()
  vfs: dentry_unhash immediately prior to rmdir
  vfs: Block mmapped writes while the fs is frozen
  ...
2011-05-26 09:52:14 -07:00
Sage Weil
51892bbb57 vfs: clean up vfs_rename_other
Simplify control flow to match vfs_rename_dir.

Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-05-26 07:26:53 -04:00
Sage Weil
9055cba711 vfs: clean up vfs_rename_dir
Simplify control flow through vfs_rename_dir.

Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-05-26 07:26:52 -04:00
Sage Weil
912dbc15d9 vfs: clean up vfs_rmdir
Simplify the control flow with an out label.

Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-05-26 07:26:51 -04:00
Miklos Szeredi
b5afd2c406 vfs: fix vfs_rename_dir for FS_RENAME_DOES_D_MOVE filesystems
vfs_rename_dir() doesn't properly account for filesystems with
FS_RENAME_DOES_D_MOVE.  If new_dentry has a target inode attached, it
unhashes the new_dentry prior to the rename() iop and rehashes it after,
but doesn't account for the possibility that rename() may have swapped
{old,new}_dentry.  For FS_RENAME_DOES_D_MOVE filesystems, it rehashes
new_dentry (now the old renamed-from name, which d_move() expected to go
away), such that a subsequent lookup will find it.  Currently all
FS_RENAME_DOES_D_MOVE filesystems compensate for this by failing in
d_revalidate.

The bug was introduced by: commit 349457ccf2
"[PATCH] Allow file systems to manually d_move() inside of ->rename()"

Fix by not rehashing the new dentry.  Rehashing used to be needed by
d_move() but isn't anymore.

Reported-by: Sage Weil <sage@newdream.net>
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-05-26 07:26:50 -04:00
Sage Weil
a71905f0db vfs: update dentry_unhash() comment
The helper is now only called by file systems, not the VFS.

Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-05-26 07:26:49 -04:00
Sage Weil
e4eaac06bc vfs: push dentry_unhash on rename_dir into file systems
Only a few file systems need this.  Start by pushing it down into each
rename method (except gfs2 and xfs) so that it can be dealt with on a
per-fs basis.

Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-05-26 07:26:48 -04:00
Sage Weil
79bf7c732b vfs: push dentry_unhash on rmdir into file systems
Only a few file systems need this.  Start by pushing it down into each
fs rmdir method (except gfs2 and xfs) so it can be dealt with on a per-fs
basis.

This does not change behavior for any in-tree file systems.

Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-05-26 07:26:47 -04:00
Sage Weil
64252c75a2 vfs: remove dget() from dentry_unhash()
This serves no useful purpose that I can discern.  All callers (rename,
rmdir) hold their own reference to the dentry.

A quick audit of all file systems showed no relevant checks on the value
of d_count in vfs_rmdir/vfs_rename_dir paths.

Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-05-26 07:26:46 -04:00
Sage Weil
48293699a0 vfs: dentry_unhash immediately prior to rmdir
This presumes that there is no reason to unhash a dentry if we fail because
it is a mountpoint or the LSM check fails, and that the LSM checks do not
depend on the dentry being unhashed.

Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-05-26 07:26:46 -04:00
Al Viro
9f1fafee9e merge handle_reval_dot and nameidata_drop_rcu_last
new helper: complete_walk().  Done on successful completion
of walk, drops out of RCU mode, does d_revalidate of final
result if that hadn't been done already.

handle_reval_dot() and nameidata_drop_rcu_last() subsumed into
that one; callers converted to use of complete_walk().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-05-26 07:26:32 -04:00
Al Viro
19660af736 consolidate nameidata_..._drop_rcu()
Merge these into a single function (unlazy_walk(nd, dentry)),
kill ..._maybe variants

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-05-26 07:26:02 -04:00
Erez Zadok
1a4022f88d VFS: move BUG_ON test for symlink nd->depth after current->link_count test
This solves a serious VFS-level bug in nested_symlink (which was
rewritten from do_follow_link), and follows the order of depth tests
that existed before.

The bug triggers a BUG_ON in fs/namei.c:1381, when running racer with
symlink and rename ops.

Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>
Acked-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-05-21 00:12:16 -07:00
Linus Torvalds
26cf46be95 vfs: micro-optimize acl_permission_check()
It's a hot function, and we're better off not mixing types in the mask
calculations.  The compiler just ends up mixing 16-bit and 32-bit
operations, for no good reason.

So do everything in 'unsigned int' rather than mixing 'unsigned int'
masking with a 'umode_t' (16-bit) mode variable.

This, together with the parent commit (47a150edc2: "Cache user_ns in
struct cred") makes acl_permission_check() much nicer.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-05-13 11:51:01 -07:00
Tim Chen
c1530019e3 vfs: Fix absolute RCU path walk failures due to uninitialized seq number
During RCU walk in path_lookupat and path_openat, the rcu lookup
frequently failed if looking up an absolute path, because when root
directory was looked up, seq number was not properly set in nameidata.

We dropped out of RCU walk in nameidata_drop_rcu due to mismatch in
directory entry's seq number.  We reverted to slow path walk that need
to take references.

With the following patch, I saw a 50% increase in an exim mail server
benchmark throughput on a 4-socket Nehalem-EX system.

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Cc: stable@kernel.org (v2.6.38)
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-04-15 15:28:12 -07:00
Lucas De Marchi
25985edced Fix common misspellings
Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
2011-03-31 11:26:23 -03:00
Ian Kent
62a7375e5d vfs - check non-mountpoint dentry might block in __follow_mount_rcu()
When following a mount in rcu-walk mode we must check if the incoming dentry
is telling us it may need to block, even if it isn't actually a mountpoint.

Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-03-24 14:24:32 -04:00
Linus Torvalds
b81a618dcd Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6:
  deal with races in /proc/*/{syscall,stack,personality}
  proc: enable writing to /proc/pid/mem
  proc: make check_mem_permission() return an mm_struct on success
  proc: hold cred_guard_mutex in check_mem_permission()
  proc: disable mem_write after exec
  mm: implement access_remote_vm
  mm: factor out main logic of access_process_vm
  mm: use mm_struct to resolve gate vma's in __get_user_pages
  mm: arch: rename in_gate_area_no_task to in_gate_area_no_mm
  mm: arch: make in_gate_area take an mm_struct instead of a task_struct
  mm: arch: make get_gate_vma take an mm_struct instead of a task_struct
  x86: mark associated mm when running a task in 32 bit compatibility mode
  x86: add context tag to mark mm when running a task in 32-bit compatibility mode
  auxv: require the target to be tracable (or yourself)
  close race in /proc/*/environ
  report errors in /proc/*/*map* sanely
  pagemap: close races with suid execve
  make sessionid permissions in /proc/*/task/* match those in /proc/*
  fix leaks in path_lookupat()

Fix up trivial conflicts in fs/proc/base.c
2011-03-23 20:51:42 -07:00
Serge E. Hallyn
2e14967075 userns: rename is_owner_or_cap to inode_owner_or_capable
And give it a kernel-doc comment.

[akpm@linux-foundation.org: btrfs changed in linux-next]
Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Daniel Lezcano <daniel.lezcano@free.fr>
Acked-by: David Howells <dhowells@redhat.com>
Cc: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-03-23 19:47:13 -07:00
Serge E. Hallyn
e795b71799 userns: userns: check user namespace for task->file uid equivalence checks
Cheat for now and say all files belong to init_user_ns.  Next step will be
to let superblocks belong to a user_ns, and derive inode_userns(inode)
from inode->i_sb->s_user_ns.  Finally we'll introduce more flexible
arrangements.

Changelog:
	Feb 15: make is_owner_or_cap take const struct inode
	Feb 23: make is_owner_or_cap bool

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Daniel Lezcano <daniel.lezcano@free.fr>
Acked-by: David Howells <dhowells@redhat.com>
Cc: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-03-23 19:47:08 -07:00
Al Viro
bd23a539d0 fix leaks in path_lookupat()
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-03-23 09:56:55 -04:00
Al Viro
1aed3e4204 lose 'mounting_here' argument in ->d_manage()
it's always false...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-03-18 10:01:59 -04:00
Al Viro
7cc90cc3ff don't pass 'mounting_here' flag to follow_down()
it's always false now

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-03-18 09:04:20 -04:00
Al Viro
0e794589e5 fix follow_link() breakage
commit 574197e0de had a missing
piece, breaking the loop detection ;-/

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-03-16 04:57:03 -04:00
Al Viro
574197e0de tidy the trailing symlinks traversal up
* pull the handling of current->total_link_count into
__do_follow_link()
* put the common "do ->put_link() if needed and path_put() the link"
  stuff into a helper (put_link(nd, link, cookie))
* rename __do_follow_link() to follow_link(), while we are at it

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-03-15 17:16:25 -04:00
Al Viro
b356379a02 Turn resolution of trailing symlinks iterative everywhere
The last remaining place (resolution of nested symlink) converted
to the loop of the same kind we have in path_lookupat() and
path_openat().

Note that we still *do* have a recursion in pathname resolution;
can't avoid it, really.  However, it's strictly for nested symlinks
now - i.e. ones in the middle of a pathname.

link_path_walk() has lost the tail now - it always walks everything
except the last component.

do_follow_link() renamed to nested_symlink() and moved down.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-03-15 17:16:25 -04:00
Al Viro
ce0525449d simplify link_path_walk() tail
Now that link_path_walk() is called without LOOKUP_PARENT
only from do_follow_link(), we can simplify the checks in
last component handling.  First of all, checking if we'd
arrived to a directory is not needed - the caller will check
it anyway.  And LOOKUP_FOLLOW is guaranteed to be there,
since we only get to that place with nd->depth > 0.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-03-15 17:16:25 -04:00
Al Viro
bd92d7fed8 Make trailing symlink resolution in path_lookupat() iterative
Now the only caller of link_path_walk() that does *not* pass
LOOKUP_PARENT is do_follow_link()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-03-15 17:16:25 -04:00
Al Viro
b21041d0f7 update nd->inode in __do_follow_link() instead of after do_follow_link()
... and note that we only need to do it for LAST_BIND symlinks

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-03-15 17:16:25 -04:00
Al Viro
ce57dfc179 pull handling of one pathname component into a helper
new helper: walk_component().  Handles everything except symlinks;
returns negative on error, 0 on success and 1 on symlinks we decided
to follow.  Drops out of RCU mode on such symlinks.

link_path_walk() and do_last() switched to using that.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-03-15 17:16:20 -04:00
Aneesh Kumar K.V
11a7b371b6 fs: allow AT_EMPTY_PATH in linkat(), limit that to CAP_DAC_READ_SEARCH
We don't want to allow creation of private hardlinks by different application
using the fd passed to them via SCM_RIGHTS. So limit the null relative name
usage in linkat syscall to CAP_DAC_READ_SEARCH

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
2011-03-15 17:16:05 -04:00
Al Viro
bcda76524c Allow O_PATH for symlinks
At that point we can't do almost nothing with them.  They can be opened
with O_PATH, we can manipulate such descriptors with dup(), etc. and
we can see them in /proc/*/{fd,fdinfo}/*.

We can't (and won't be able to) follow /proc/*/fd/* symlinks for those;
there's simply not enough information for pathname resolution to go on
from such point - to resolve a symlink we need to know which directory
does it live in.

We will be able to do useful things with them after the next commit, though -
readlinkat() and fchownat() will be possible to use with dfd being an
O_PATH-opened symlink and empty relative pathname.  Combined with
open_by_handle() it'll give us a way to do realink-by-handle and
lchown-by-handle without messing with more redundant syscalls.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-03-15 02:21:45 -04:00
Al Viro
1abf0c718f New kind of open files - "location only".
New flag for open(2) - O_PATH.  Semantics:
	* pathname is resolved, but the file itself is _NOT_ opened
as far as filesystem is concerned.
	* almost all operations on the resulting descriptors shall
fail with -EBADF.  Exceptions are:
	1) operations on descriptors themselves (i.e.
		close(), dup(), dup2(), dup3(), fcntl(fd, F_DUPFD),
		fcntl(fd, F_DUPFD_CLOEXEC, ...), fcntl(fd, F_GETFD),
		fcntl(fd, F_SETFD, ...))
	2) fcntl(fd, F_GETFL), for a common non-destructive way to
		check if descriptor is open
	3) "dfd" arguments of ...at(2) syscalls, i.e. the starting
		points of pathname resolution
	* closing such descriptor does *NOT* affect dnotify or
posix locks.
	* permissions are checked as usual along the way to file;
no permission checks are applied to the file itself.  Of course,
giving such thing to syscall will result in permission checks (at
the moment it means checking that starting point of ....at() is
a directory and caller has exec permissions on it).

fget() and fget_light() return NULL on such descriptors; use of
fget_raw() and fget_raw_light() is needed to get them.  That protects
existing code from dealing with those things.

There are two things still missing (they come in the next commits):
one is handling of symlinks (right now we refuse to open them that
way; see the next commit for semantics related to those) and another
is descriptor passing via SCM_RIGHTS datagrams.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-03-15 02:21:45 -04:00
Aneesh Kumar K.V
aae8a97d3e fs: Don't allow to create hardlink for deleted file
Add inode->i_nlink == 0 check in VFS. Some of the file systems
do this internally. A followup patch will remove those instance.
This is needed to ensure that with link by handle we don't allow
to create hardlink of an unlinked file. The check also prevent a race
between unlink and link

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-03-15 02:21:44 -04:00
Al Viro
f52e0c1130 New AT_... flag: AT_EMPTY_PATH
For name_to_handle_at(2) we'll want both ...at()-style syscall that
would be usable for non-directory descriptors (with empty relative
pathname).  Introduce new flag (AT_EMPTY_PATH) to deal with that and
corresponding LOOKUP_EMPTY; teach user_path_at() and path_init() to
deal with the latter.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-03-14 19:12:20 -04:00
Al Viro
73d049a40f open-style analog of vfs_path_lookup()
new function: file_open_root(dentry, mnt, name, flags) opens the file
vfs_path_lookup would arrive to.

Note that name can be empty; in that case the usual requirement that
dentry should be a directory is lifted.

open-coded equivalents switched to it, may_open() got down exactly
one caller and became static.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-03-14 09:15:28 -04:00
Al Viro
5b6ca027d8 reduce vfs_path_lookup() to do_path_lookup()
New lookup flag: LOOKUP_ROOT.  nd->root is set (and held) by caller,
path_init() starts walking from that place and all pathname resolution
machinery never drops nd->root if that flag is set.  That turns
vfs_path_lookup() into a special case of do_path_lookup() *and*
gets us down to 3 callers of link_path_walk(), making it finally
feasible to rip the handling of trailing symlink out of link_path_walk().
That will not only simply the living hell out of it, but make life
much simpler for unionfs merge.  Trailing symlink handling will
become iterative, which is a good thing for stack footprint in
a lot of situations as well.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-03-14 09:15:27 -04:00
Al Viro
5a18fff209 untangle do_lookup()
That thing has devolved into rats nest of gotos; sane use of unlikely()
gets rid of that horror and gives much more readable structure:
	* make a fast attempt to find a dentry; false negatives are OK.
In RCU mode if everything went fine, we are done, otherwise just drop
out of RCU.  If we'd done (RCU) ->d_revalidate() and it had not refused
outright (i.e. didn't give us -ECHILD), remember its result.
	* now we are not in RCU mode and hopefully have a dentry.  If we
do not, lock parent, do full d_lookup() and if that has not found anything,
allocate and call ->lookup().  If we'd done that ->lookup(), remember that
dentry is good and we don't need to revalidate it.
	* now we have a dentry.  If it has ->d_revalidate() and we can't
skip it, call it.
	* hopefully dentry is good; if not, either fail (in case of error)
or try to invalidate it.  If d_invalidate() has succeeded, drop it and
retry everything as if original attempt had not found a dentry.
	* now we can finish it up - deal with mountpoint crossing and
automount.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-03-14 09:15:27 -04:00
Al Viro
40b39136f0 path_openat: clean ELOOP handling a bit
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2011-03-14 09:15:27 -04:00