Re: [PATCH bpf-next v4 1/6] bpf, sockmap: reject overflowing copy + len in bpf_msg_push_data()

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

On Mon, Jun 15, 2026 at 10:19:54AM +0800, Jiayuan Chen wrote:
>From: Weiming Shi <bestswngs@gmail.com>
>
>When the scatterlist ring is full or nearly full, bpf_msg_push_data()
>enters a copy fallback path and computes copy + len for the page
>allocation size. Since len comes from BPF with arg3_type = ARG_ANYTHING
>and both are u32, a crafted len can wrap the sum to a small value,
>causing an undersized allocation followed by an out-of-bounds memcpy.
>
> BUG: unable to handle page fault for address: ffffed104089a402
> Oops: Oops: 0000 [#1] SMP KASAN NOPTI
> Call Trace:
>  __asan_memcpy (mm/kasan/shadow.c:105)
>  bpf_msg_push_data (net/core/filter.c:2852 net/core/filter.c:2788)
>  bpf_prog_9ed8b5711920a7d7+0x2e/0x36
>  sk_psock_msg_verdict (net/core/skmsg.c:934)
>  tcp_bpf_sendmsg (net/ipv4/tcp_bpf.c:421 net/ipv4/tcp_bpf.c:584)
>  __sys_sendto (net/socket.c:2206)
>  do_syscall_64 (arch/x86/entry/syscall_64.c:94)
>  entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
>
>Add an overflow check before the allocation.
>
>Link: https://lore.kernel.org/all/20260424155913.A19FDC19425@smtp.kernel.org
>Fixes: 6fff607e2f14 ("bpf: sk_msg program helper bpf_msg_push_data")
>Tested-by: Xiang Mei <xmei5@asu.edu>
>Tested-by: Xinyu Ma <mmmxny@gmail.com>
>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>