kernel/relay.c: fix read_pos error when multiple readers

stable inclusion
from stable-v4.19.283
commit 2a6c63d04d89227ee45d0234c8059e2bccc15d73
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I7E5C1


CVE: CVE-2023-3268

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[ Upstream commit 341a7213 ]

When reading, read_pos should start with bytes_consumed, not file->f_pos.
Because when there is more than one reader, the read_pos corresponding to
file->f_pos may have been consumed, which will cause the data that has
been consumed to be read and the bytes_consumed update error.

Signed-off-by: Pengcheng Yang <yangpc@wangsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jann Horn <jannh@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>e
Link: http://lkml.kernel.org/r/1579691175-28949-1-git-send-email-yangpc@wangsu.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Stable-dep-of: 43ec16f1 ("relayfs: fix out-of-bounds access in relay_file_read")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: GONG, Ruiqi <gongruiqi1@huawei.com>
Reviewed-by: Wang Weiyang <wangweiyang2@huawei.com>
Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>