linux-kernel - [PATCH] locks: fix possible infinite loop in posix deadlock detection

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20071028173136.GA16905@fieldses.org>
Date:	Sun, 28 Oct 2007 13:31:37 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>, stable@...nel.org
Cc:	linux-kernel@...r.kernel.org,
	"George G. Davis" <gdavis@...sta.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org
Subject: [PATCH] locks: fix possible infinite loop in posix deadlock
	detection

From: J. Bruce Fields <bfields@...i.umich.edu>

I think the real solution is to remove deadlock detection completely;
it's hard to imaagine applications really depend on it anyway.

For now, though, just bail out after a few iterations.

Thanks to George Davis for reporting the problem.

Cc: "George G. Davis" <gdavis@...sta.com>
Signed-off-by: J. Bruce Fields <bfields@...i.umich.edu>
---
 fs/locks.c |   12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index 0127a28..131aa88 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -696,17 +696,29 @@ EXPORT_SYMBOL(posix_test_lock);
  * Note: the above assumption may not be true when handling lock requests
  * from a broken NFS client. But broken NFS clients have a lot more to
  * worry about than proper deadlock detection anyway... --okir
+ *
+ * However, the failure of this assumption (also possible in the case of
+ * multiple tasks sharing the same open file table) also means there's no
+ * guarantee that the loop below will terminate.  As a hack, we give up
+ * after a few iterations.  We don't bother returning EDEADLK in that case;
+ * the deadlock has probably already happened anyway.
  */
+
+#define MAX_DEADLK_ITERATIONS 10
+
 static int posix_locks_deadlock(struct file_lock *caller_fl,
 				struct file_lock *block_fl)
 {
 	struct file_lock *fl;
+	int i = 0;
 
 next_task:
 	if (posix_same_owner(caller_fl, block_fl))
 		return 1;
 	list_for_each_entry(fl, &blocked_list, fl_link) {
 		if (posix_same_owner(fl, block_fl)) {
+			if (i++ > MAX_DEADLK_ITERATIONS)
+				return 0;
 			fl = fl->fl_next;
 			block_fl = fl;
 			goto next_task;
-- 
1.5.3.4.208.gc990

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/