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    Subject[PATCH 6.0 254/862] bpf: Propagate error from htab_lock_bucket() to userspace
    Date
    From: Hou Tao <houtao1@huawei.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@gmail.com>
    Signed-off-by: Hou Tao <houtao1@huawei.com>
    Link: https://lore.kernel.org/r/20220831042629.130006-3-houtao@huaweicloud.com
    Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.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


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