Re: [PATCH bpf-next v4 2/6] bpf, sockmap: Fix wrong rsge offset in bpf_msg_push_data()

[John Fastabend <john.fastabend@gmail.com>]

On Mon, Jun 15, 2026 at 10:19:55AM +0800, Jiayuan Chen wrote:
>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>
>Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
>Signed-off-by: Weiming Shi <bestswngs@gmail.com>
>Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
>---

Reviewed-by: John Fastabend <john.fastabend@gmail.com>