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authorAl Viro <viro@zeniv.linux.org.uk>2012-09-21 08:19:02 -0400
committerAl Viro <viro@zeniv.linux.org.uk>2012-09-22 20:48:18 -0400
commit156cacb1d0d36b0d0582d9e798e58e0044f516b3 (patch)
tree79eddbde8671b1899d77dcfabb3ae3e21ce39072
parentfea7a08acb13524b47711625eebea40a0ede69a0 (diff)
do_add_mount()/umount -l races
normally we deal with lock_mount()/umount races by checking that mountpoint to be is still in our namespace after lock_mount() has been done. However, do_add_mount() skips that check when called with MNT_SHRINKABLE in flags (i.e. from finish_automount()). The reason is that ->mnt_ns may be a temporary namespace created exactly to contain automounts a-la NFS4 referral handling. It's not the namespace of the caller, though, so check_mnt() would fail here. We still need to check that ->mnt_ns is non-NULL in that case, though. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
-rw-r--r--fs/namespace.c10
1 files changed, 8 insertions, 2 deletions
diff --git a/fs/namespace.c b/fs/namespace.c
index 4d31f73e256..7bdf7907413 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1886,8 +1886,14 @@ static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags)
return err;
err = -EINVAL;
- if (!(mnt_flags & MNT_SHRINKABLE) && !check_mnt(real_mount(path->mnt)))
- goto unlock;
+ if (unlikely(!check_mnt(real_mount(path->mnt)))) {
+ /* that's acceptable only for automounts done in private ns */
+ if (!(mnt_flags & MNT_SHRINKABLE))
+ goto unlock;
+ /* ... and for those we'd better have mountpoint still alive */
+ if (!real_mount(path->mnt)->mnt_ns)
+ goto unlock;
+ }
/* Refuse the same filesystem on the same mount point */
err = -EBUSY;