This is a note to let you know that I've just added the patch titled
lockd: protect nlm_blocked access in nlmsvc_retry_blocked
to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
lockd-protect-nlm_blocked-access-in-nlmsvc_retry_blocked.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 1c327d962fc420aea046c16215a552710bde8231 Mon Sep 17 00:00:00 2001
From: David Jeffery <djeffery@xxxxxxxxxx>
Date: Wed, 10 Jul 2013 13:19:50 -0400
Subject: lockd: protect nlm_blocked access in nlmsvc_retry_blocked
From: David Jeffery <djeffery@xxxxxxxxxx>
commit 1c327d962fc420aea046c16215a552710bde8231 upstream.
In nlmsvc_retry_blocked, the check that the list is non-empty and acquiring
the pointer of the first entry is unprotected by any lock. This allows a rare
race condition when there is only one entry on the list. A function such as
nlmsvc_grant_callback() can be called, which will temporarily remove the entry
from the list. Between the list_empty() and list_entry(),the list may become
empty, causing an invalid pointer to be used as an nlm_block, leading to a
possible crash.
This patch adds the nlm_block_lock around these calls to prevent concurrent
use of the nlm_blocked list.
This was a regression introduced by
f904be9cc77f361d37d71468b13ff3d1a1823dea "lockd: Mostly remove BKL from
the server".
Signed-off-by: David Jeffery <djeffery@xxxxxxxxxx>
Cc: Bryan Schumaker <bjschuma@xxxxxxxxxx>
Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/lockd/svclock.c | 4 ++++
1 file changed, 4 insertions(+)
--- a/fs/lockd/svclock.c
+++ b/fs/lockd/svclock.c
@@ -941,6 +941,7 @@ nlmsvc_retry_blocked(void)
unsigned long timeout = MAX_SCHEDULE_TIMEOUT;
struct nlm_block *block;
+ spin_lock(&nlm_blocked_lock);
while (!list_empty(&nlm_blocked) && !kthread_should_stop()) {
block = list_entry(nlm_blocked.next, struct nlm_block, b_list);
@@ -950,6 +951,7 @@ nlmsvc_retry_blocked(void)
timeout = block->b_when - jiffies;
break;
}
+ spin_unlock(&nlm_blocked_lock);
dprintk("nlmsvc_retry_blocked(%p, when=%ld)\n",
block, block->b_when);
@@ -959,7 +961,9 @@ nlmsvc_retry_blocked(void)
retry_deferred_block(block);
} else
nlmsvc_grant_blocked(block);
+ spin_lock(&nlm_blocked_lock);
}
+ spin_unlock(&nlm_blocked_lock);
return timeout;
}
Patches currently in stable-queue which might be from djeffery@xxxxxxxxxx are
queue-3.4/lockd-protect-nlm_blocked-access-in-nlmsvc_retry_blocked.patch
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