Re: [PATCH bpf-next v3 2/7] bpf, sockmap: Fix wrong rsge offset in bpf_msg_push_data()

[Kuniyuki Iwashima <kuniyu@google.com>]

From: Jiayuan Chen <jiayuan.chen@linux.dev>
Date: Fri, 12 Jun 2026 21:07:46 +0800
> From: Weiming Shi <bestswngs@gmail.com>
> 
> When bpf_msg_push_data() splits a scatterlist element into head and
> tail, the tail's page offset is advanced by `start` (absolute message
> byte offset) instead of `start - offset` (byte position within the
> element). This makes rsge.offset overshoot by `offset` bytes, pointing
> to the wrong location within the page or beyond its boundary. Consumers
> of the corrupted entry either silently read wrong data or trigger an
> out-of-bounds access.
> 
>  BUG: KASAN: slab-use-after-free in bpf_msg_pull_data (net/core/filter.c:2728)
>  Read of size 32752 at addr ffff8881042f0010 by task poc/130
>  Call Trace:
>   __asan_memcpy (mm/kasan/shadow.c:105)
>   bpf_msg_pull_data (net/core/filter.c:2728)
>   bpf_prog_run_pin_on_cpu (include/linux/bpf.h:1402)
>   sk_psock_msg_verdict (net/core/skmsg.c:934)
>   tcp_bpf_send_verdict (net/ipv4/tcp_bpf.c:421)
>   sock_sendmsg_nosec (net/socket.c:727)
> 
> Fixes: 6fff607e2f14 ("bpf: sk_msg program helper bpf_msg_push_data")
> Reported-by: Xiang Mei <xmei5@asu.edu>
> Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>
> Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
> Signed-off-by: Weiming Shi <bestswngs@gmail.com>
> Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>

Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>