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.
Signed-off-by: David Jeffery <djeffery@xxxxxxxxxx>
--- a/fs/lockd/svclock.c
+++ b/fs/lockd/svclock.c
@@ -951,6 +951,7 @@ 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);
@@ -960,6 +961,7 @@ 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);
@@ -969,7 +971,9 @@ 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;
}
--
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