Commit 6d4b9e38 authored Dec 26, 2011 by Linus Torvalds

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



Bruce Fields notes that commit 778fc546 ("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>

parent 4962516b

fs/locks.c

+3 −8

Original line number	Diff line number	Diff line
		@@ -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;
		@@ -1284,7 +1280,6 @@ int __break_lease(struct inode *inode, unsigned int mode)

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