linux-kernel - [PATCH 6.0 254/862] bpf: Propagate error from htab_lock

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Message-Id: <20221019083301.276436592@linuxfoundation.org>
Date:   Wed, 19 Oct 2022 10:25:41 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Hao Sun <sunhao.th@...il.com>,
        Hou Tao <houtao1@...wei.com>,
        Martin KaFai Lau <martin.lau@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 6.0 254/862] bpf: Propagate error from htab_lock_bucket() to userspace

From: Hou Tao <houtao1@...wei.com>

[ Upstream commit 66a7a92e4d0d091e79148a4c6ec15d1da65f4280 ]

In __htab_map_lookup_and_delete_batch() if htab_lock_bucket() returns
-EBUSY, it will go to next bucket. Going to next bucket may not only
skip the elements in current bucket silently, but also incur
out-of-bound memory access or expose kernel memory to userspace if
current bucket_cnt is greater than bucket_size or zero.

Fixing it by stopping batch operation and returning -EBUSY when
htab_lock_bucket() fails, and the application can retry or skip the busy
batch as needed.

Fixes: 20b6cc34ea74 ("bpf: Avoid hashtab deadlock with map_locked")
Reported-by: Hao Sun <sunhao.th@...il.com>
Signed-off-by: Hou Tao <houtao1@...wei.com>
Link: https://lore.kernel.org/r/20220831042629.130006-3-houtao@huaweicloud.com
Signed-off-by: Martin KaFai Lau <martin.lau@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/bpf/hashtab.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index ad09da139589..75f77df910dc 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -1704,8 +1704,11 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
 	/* do not grab the lock unless need it (bucket_cnt > 0). */
 	if (locked) {
 		ret = htab_lock_bucket(htab, b, batch, &flags);
-		if (ret)
-			goto next_batch;
+		if (ret) {
+			rcu_read_unlock();
+			bpf_enable_instrumentation();
+			goto after_loop;
+		}
 	}
 
 	bucket_cnt = 0;
-- 
2.35.1