Commit 1c327d96 authored by David Jeffery's avatar David Jeffery Committed by J. Bruce Fields

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
f904be9c  "lockd: Mostly remove BKL from
the server".

Cc: Bryan Schumaker <>
Signed-off-by: default avatarDavid Jeffery <>
Signed-off-by: default avatarJ. Bruce Fields <>
parent d1091481
......@@ -939,6 +939,7 @@ nlmsvc_retry_blocked(void)
unsigned long timeout = MAX_SCHEDULE_TIMEOUT;
struct nlm_block *block;
while (!list_empty(&nlm_blocked) && !kthread_should_stop()) {
block = list_entry(, struct nlm_block, b_list);
......@@ -948,6 +949,7 @@ nlmsvc_retry_blocked(void)
timeout = block->b_when - jiffies;
dprintk("nlmsvc_retry_blocked(%p, when=%ld)\n",
block, block->b_when);
......@@ -957,7 +959,9 @@ nlmsvc_retry_blocked(void)
} else
return timeout;
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