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]
Date:   Sun, 16 Jul 2017 14:56:38 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Ben Hutchings" <ben.hutchings@...ethink.co.uk>,
        "Takashi Iwai" <tiwai@...e.de>
Subject: [PATCH 3.2 77/95] ALSA: seq: Don't break snd_use_lock_sync() loop
 by timeout

3.2.91-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@...e.de>

commit 4e7655fd4f47c23e5249ea260dc802f909a64611 upstream.

The snd_use_lock_sync() (thus its implementation
snd_use_lock_sync_helper()) has the 5 seconds timeout to break out of
the sync loop.  It was introduced from the beginning, just to be
"safer", in terms of avoiding the stupid bugs.

However, as Ben Hutchings suggested, this timeout rather introduces a
potential leak or use-after-free that was apparently fixed by the
commit 2d7d54002e39 ("ALSA: seq: Fix race during FIFO resize"):
for example, snd_seq_fifo_event_in() -> snd_seq_event_dup() ->
copy_from_user() could block for a long time, and snd_use_lock_sync()
goes timeout and still leaves the cell at releasing the pool.

For fixing such a problem, we remove the break by the timeout while
still keeping the warning.

Suggested-by: Ben Hutchings <ben.hutchings@...ethink.co.uk>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 sound/core/seq/seq_lock.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

--- a/sound/core/seq/seq_lock.c
+++ b/sound/core/seq/seq_lock.c
@@ -28,19 +28,16 @@
 /* wait until all locks are released */
 void snd_use_lock_sync_helper(snd_use_lock_t *lockp, const char *file, int line)
 {
-	int max_count = 5 * HZ;
+	int warn_count = 5 * HZ;
 
 	if (atomic_read(lockp) < 0) {
 		printk(KERN_WARNING "seq_lock: lock trouble [counter = %d] in %s:%d\n", atomic_read(lockp), file, line);
 		return;
 	}
 	while (atomic_read(lockp) > 0) {
-		if (max_count == 0) {
-			snd_printk(KERN_WARNING "seq_lock: timeout [%d left] in %s:%d\n", atomic_read(lockp), file, line);
-			break;
-		}
+		if (warn_count-- == 0)
+			pr_warn("ALSA: seq_lock: waiting [%d left] in %s:%d\n", atomic_read(lockp), file, line);
 		schedule_timeout_uninterruptible(1);
-		max_count--;
 	}
 }
 

Powered by blists - more mailing lists