blob: 99c5c860b9d780771a762ebf83af7849cc2e1095 [file] [log] [blame]
From 0c95a88acbeb7ba45179edbe0a95375eb3bb6b8f Mon Sep 17 00:00:00 2001
From: yangerkun <>
Date: Wed, 4 Mar 2020 15:25:56 +0800
Subject: [PATCH] locks: fix a potential use-after-free problem when wakeup a
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commit 6d390e4b5d48ec03bb87e63cf0a2bff5f4e116da upstream.
'16306a61d3b7 ("fs/locks: always delete_block after waiting.")' add the
logic to check waiter->fl_blocker without blocked_lock_lock. And it will
trigger a UAF when we try to wakeup some waiter
Thread 1 has create a write flock a on file, and now thread 2 try to
unlock and delete flock a, thread 3 try to add flock b on the same file.
Thread2 Thread3
flock syscall(create flock b)
flock_lock_inode(will insert
our fl_blocked_member list
to flock a's fl_blocked_requests)
flock syscall(unlock)
b->fl_blocker = NULL)
break by a signal
b->fl_blocker == NULL &&
success, return directly
locks_free_lock b
trigger UAF
Fix it by remove this logic, and this patch may also fix CVE-2019-19769.
Fixes: 16306a61d3b7 ("fs/locks: always delete_block after waiting.")
Signed-off-by: yangerkun <>
Signed-off-by: Jeff Layton <>
Signed-off-by: Paul Gortmaker <>
diff --git a/fs/locks.c b/fs/locks.c
index 09585a548f4f..e0c920ff599e 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -757,20 +757,6 @@ int locks_delete_block(struct file_lock *waiter)
int status = -ENOENT;
- /*
- * If fl_blocker is NULL, it won't be set again as this thread
- * "owns" the lock and is the only one that might try to claim
- * the lock. So it is safe to test fl_blocker locklessly.
- * Also if fl_blocker is NULL, this waiter is not listed on
- * fl_blocked_requests for some lock, so no other request can
- * be added to the list of fl_blocked_requests for this
- * request. So if fl_blocker is NULL, it is safe to
- * locklessly check if fl_blocked_requests is empty. If both
- * of these checks succeed, there is no need to take the lock.
- */
- if (waiter->fl_blocker == NULL &&
- list_empty(&waiter->fl_blocked_requests))
- return status;
if (waiter->fl_blocker)
status = 0;