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  1. 16 Jun, 2011 2 commits
    • Al Viro's avatar
      VFS: Fix vfsmount overput on simultaneous automount · 8aef1884
      Al Viro authored 
      [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: default avatarJeff Layton <jlayton@redhat.com>
Tested-by: default avatarIan Kent <raven@themaw.net>
Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      8aef1884
    • Török Edwin's avatar
      fix wrong iput on d_inode introduced by e6bc45d6 · 50338b88
      Török Edwin authored 
      Git bisection shows that commit e6bc45d6 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/2011/6/15/50Reported-by: default avatarNorbert Preining <preining@logic.at>
Reported-by: default avatarTörök Edwin <edwintorok@gmail.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarTörök Edwin <edwintorok@gmail.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      50338b88
  3. 12 Jun, 2011 6 commits
    • Al Viro's avatar
      Delay struct net freeing while there's a sysfs instance refering to it · a685e089
      Al Viro authored 
      	* new refcount in struct net, controlling actual freeing of the memory
	* new method in kobj_ns_type_operations (->drop_ns())
	* ->current_ns() semantics change - it's supposed to be followed by
corresponding ->drop_ns().  For struct net in case of CONFIG_NET_NS it bumps
the new refcount; net_drop_ns() decrements it and calls net_free() if the
last reference has been dropped.  Method renamed to ->grab_current_ns().
	* old net_free() callers call net_drop_ns() instead.
	* sysfs_exit_ns() is gone, along with a large part of callchain
leading to it; now that the references stored in ->ns[...] stay valid we
do not need to hunt them down and replace them with NULL.  That fixes
problems in sysfs_lookup() and sysfs_readdir(), along with getting rid
of sb->s_instances abuse.

	Note that struct net *shutdown* logics has not changed - net_cleanup()
is called exactly when it used to be called.  The only thing postponed by
having a sysfs instance refering to that struct net is actual freeing of
memory occupied by struct net.
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      a685e089
    • Al Viro's avatar
      afs: fix sget() races, close leak on umount · dde194a6
      Al Viro authored 
      * set ->s_fs_info in set() callback passed to sget()
* allocate the thing and set it up enough for afs_test_super() before
making it visible
* have it freed in ->kill_sb() (current tree simply leaks it)
* have ->put_super() leave ->s_fs_info->volume alone; it's too early for
dropping it; do that from ->kill_sb() after having called kill_anon_super().
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      dde194a6
    • Al Viro's avatar
      ubifs: fix sget races · d251ed27
      Al Viro authored 
      * allocate ubifs_info in ->mount(), fill it enough for sb_test() and
set ->s_fs_info to it in set() callback passed to sget().
* do *not* free it in ->put_super(); do that in ->kill_sb() after we'd
done kill_anon_super().
* don't free it in ubifs_fill_super() either - deactivate_locked_super()
done by caller when ubifs_fill_super() returns an error will take care
of that sucker.
* get rid of kludge with passing ubi to ubifs_fill_super() in ->s_fs_info;
we only need it in alloc_ubifs_info(), so ubifs_fill_super() will need
only ubifs_info.  Which it will find in ->s_fs_info just fine, no need to
reassign anything...

As the result, sb_test() becomes safe to apply to all superblocks that
can be found by sget() (and a kludge with temporary use of ->s_fs_info
to store a pointer to very different structure goes away).
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      d251ed27
    • Al Viro's avatar
      ubifs: split allocation of ubifs_info into a separate function · b1c27ab3
      Al Viro authored 
      preparation to ubifs sget() race fixes
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      b1c27ab3
    • Al Viro's avatar
      fix leak in proc_set_super() · ff78fca2
      Al Viro authored 
      set_anon_super() can fail...
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
      ff78fca2
    • Linus Torvalds's avatar
      Merge branch 'for-linus' of... · b99ca60c
      Linus Torvalds authored 
      Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/security-testing-2.6

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/security-testing-2.6:
  AppArmor: Fix sleep in invalid context from task_setrlimit
      b99ca60c
  5. 11 Jun, 2011 1 commit
  7. 10 Jun, 2011 1 commit
  9. 09 Jun, 2011 30 commits
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