Re: file locking fix for 3.2

From: Linus Torvalds
Date: Mon Dec 26 2011 - 13:38:47 EST

I'm committing the appended version instead. It removes all the games with
IS_ERR(), and just does the checking at the allocation point, the way the
other lease_alloc() user does too.

Holler if you see something odd in there..

commit 6d4b9e38d3980826abccfbd90e95bf4bd41b8dd2
Author: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Date: Mon Dec 26 10:25:26 2011 -0800

vfs: fix handling of lock allocation failure in lease-break case

Bruce Fields notes that commit 778fc546f749 ("locks: fix tracking of
inprogress lease breaks") introduced a possible error pointer
dereference on failure to allocate memory. locks_conflict() will
dereference the passed-in new lease lock structure that may be an error pointer.

This means an open (without O_NONBLOCK set) on a file with a lease
applied (generally only done when Samba or nfsd (with v4) is running)
could crash if a kmalloc() fails.

So instead of playing games with IS_ERROR() all over the place, just
check the allocation failure early. That makes the code more
straightforward, and avoids this possible bad pointer dereference.

Based-on-patch-by: J. Bruce Fields <bfields@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
fs/locks.c | 11 +++--------
1 files changed, 3 insertions(+), 8 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index 3b0d05dcd7c1..637694bf3a03 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1205,6 +1205,8 @@ int __break_lease(struct inode *inode, unsigned int mode)
int want_write = (mode & O_ACCMODE) != O_RDONLY;

new_fl = lease_alloc(NULL, want_write ? F_WRLCK : F_RDLCK);
+ if (IS_ERR(new_fl))
+ return PTR_ERR(new_fl);


@@ -1221,12 +1223,6 @@ int __break_lease(struct inode *inode, unsigned int mode)
if (fl->fl_owner == current->files)
i_have_this_lease = 1;

- if (IS_ERR(new_fl) && !i_have_this_lease
- && ((mode & O_NONBLOCK) == 0)) {
- error = PTR_ERR(new_fl);
- goto out;
- }
break_time = 0;
if (lease_break_time > 0) {
break_time = jiffies + lease_break_time * HZ;
@@ -1284,8 +1280,7 @@ restart:

- if (!IS_ERR(new_fl))
- locks_free_lock(new_fl);
+ locks_free_lock(new_fl);
return error;

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