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authorDavid Jeffery <djeffery@redhat.com>2013-07-10 13:19:50 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-07-28 16:18:48 -0700
commita00c4c9f176094d7b71acd410f871b609f5e7c84 (patch)
tree3f55b6c425c57429f771fc7f230116f22bd5cead
parent101e49a9ce6fadd876ae68bddf6f155bbd02a776 (diff)
lockd: protect nlm_blocked access in nlmsvc_retry_blocked
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@redhat.com> Cc: Bryan Schumaker <bjschuma@netapp.com> Signed-off-by: J. Bruce Fields <bfields@redhat.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--fs/lockd/svclock.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c
index 6e31695d046f..db7be3a462b6 100644
--- a/fs/lockd/svclock.c
+++ b/fs/lockd/svclock.c
@@ -913,6 +913,7 @@ 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);
@@ -922,6 +923,7 @@ 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);
@@ -931,7 +933,9 @@ 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;
}