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

Bruce Fields notes that commit 778fc546f7 ("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@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2011-12-26 10:25:26 -08:00
parent 4962516b23
commit 6d4b9e38d3
1 changed files with 3 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
fs/locks.c
View File

@ -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);
lock_flocks();
@ -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:
out:
unlock_flocks();
if (!IS_ERR(new_fl))
locks_free_lock(new_fl);
locks_free_lock(new_fl);
return error;
}