tcp: seq_file: Avoid skipping sk during tcp_seek_last_pos
stable inclusion from linux-4.19.207 commit 15bf24c5fb7948564397b450ead0441143d42af2 -------------------------------- [ Upstream commit 525e2f9f ] st->bucket stores the current bucket number. st->offset stores the offset within this bucket that is the sk to be seq_show(). Thus, st->offset only makes sense within the same st->bucket. These two variables are an optimization for the common no-lseek case. When resuming the seq_file iteration (i.e. seq_start()), tcp_seek_last_pos() tries to continue from the st->offset at bucket st->bucket. However, it is possible that the bucket pointed by st->bucket has changed and st->offset may end up skipping the whole st->bucket without finding a sk. In this case, tcp_seek_last_pos() currently continues to satisfy the offset condition in the next (and incorrect) bucket. Instead, regardless of the offset value, the first sk of the next bucket should be returned. Thus, "bucket == st->bucket" check is added to tcp_seek_last_pos(). The chance of hitting this is small and the issue is a decade old, so targeting for the next tree. Fixes: a8b690f9 ("tcp: Fix slowness in read /proc/net/tcp") Signed-off-by: NMartin KaFai Lau <kafai@fb.com> Signed-off-by: NAndrii Nakryiko <andrii@kernel.org> Reviewed-by: NEric Dumazet <edumazet@google.com> Acked-by: NKuniyuki Iwashima <kuniyu@amazon.co.jp> Acked-by: NYonghong Song <yhs@fb.com> Link: https://lore.kernel.org/bpf/20210701200541.1033917-1-kafai@fb.comSigned-off-by: NSasha Levin <sashal@kernel.org> Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
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