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    Subject[PATCH AUTOSEL 5.5 482/542] bpf: map_seq_next should always increase position index
    Date
    From: Vasily Averin <vvs@virtuozzo.com>

    [ Upstream commit 90435a7891a2259b0f74c5a1bc5600d0d64cba8f ]

    If seq_file .next fuction does not change position index,
    read after some lseek can generate an unexpected output.

    See also: https://bugzilla.kernel.org/show_bug.cgi?id=206283

    v1 -> v2: removed missed increment in end of function

    Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
    Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
    Link: https://lore.kernel.org/bpf/eca84fdd-c374-a154-d874-6c7b55fc3bc4@virtuozzo.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/bpf/inode.c | 3 +--
    1 file changed, 1 insertion(+), 2 deletions(-)

    diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
    index ecf42bec38c00..6f22e0e74ef24 100644
    --- a/kernel/bpf/inode.c
    +++ b/kernel/bpf/inode.c
    @@ -196,6 +196,7 @@ static void *map_seq_next(struct seq_file *m, void *v, loff_t *pos)
    void *key = map_iter(m)->key;
    void *prev_key;

    + (*pos)++;
    if (map_iter(m)->done)
    return NULL;

    @@ -208,8 +209,6 @@ static void *map_seq_next(struct seq_file *m, void *v, loff_t *pos)
    map_iter(m)->done = true;
    return NULL;
    }
    -
    - ++(*pos);
    return key;
    }

    --
    2.20.1
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