From 1c327d962fc420aea046c16215a552710bde8231 Mon Sep 17 00:00:00 2001 From: David Jeffery Date: Wed, 10 Jul 2013 13:19:50 -0400 Subject: [PATCH] lockd: protect nlm_blocked access in nlmsvc_retry_blocked 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". Cc: Bryan Schumaker Cc: stable@vger.kernel.org Signed-off-by: David Jeffery Signed-off-by: J. Bruce Fields --- fs/lockd/svclock.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c index e703318c41df..8ebd3f551e0c 100644 --- a/fs/lockd/svclock.c +++ b/fs/lockd/svclock.c @@ -939,6 +939,7 @@ 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); @@ -948,6 +949,7 @@ 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); @@ -957,7 +959,9 @@ 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; } -- 2.30.2