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@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/locks.c b/fs/locks.c
index 3b0d05d..637694b 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1205,6 +1205,8 @@
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 @@
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 @@
out:
unlock_flocks();
- if (!IS_ERR(new_fl))
- locks_free_lock(new_fl);
+ locks_free_lock(new_fl);
return error;
}