On Thu Jun 11, 2026 at 8:34 AM EDT, Jiayuan Chen wrote: > From: Weiming Shi <[email protected]> > > 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)
Reviewed-by: Emil Tsalapatis <[email protected]> > > Fixes: 6fff607e2f14 ("bpf: sk_msg program helper bpf_msg_push_data") > Reported-by: Xiang Mei <[email protected]> > Reviewed-by: Jiayuan Chen <[email protected]> > Cc: Jiayuan Chen <[email protected]> > Signed-off-by: Weiming Shi <[email protected]> > --- > To sashiko: > > Regarding bpf_msg_push_data() reading "copy = msg->sg.data[i].length" with > i == msg->sg.end (appending at the very end of a full/near-full ring): > > This is pre-existing code, not touched by this series, and reproducing it > needs > a narrow combination -- a pure append at the end so the loop exits with > i == msg->sg.end, a full/near-full ring, plus a prior push/pop history that > leaves a stale length in the otherwise-unused end slot. A freshly built ring > zeroes that slot, so copy stays 0. We don't consider it practically > reproducible. > > Even then it's already covered: the overflow check in patch 1 ("copy + len < > copy") rejects the dangerous case, and __GFP_ZERO in patch 3 prevents any data > exposure. Not worth fixing here. > --- > net/core/filter.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/net/core/filter.c b/net/core/filter.c > index 3c8f1cedb217f..3e555f276ba80 100644 > --- a/net/core/filter.c > +++ b/net/core/filter.c > @@ -2872,7 +2872,7 @@ BPF_CALL_4(bpf_msg_push_data, struct sk_msg *, msg, > u32, start, > > psge->length = start - offset; > rsge.length -= psge->length; > - rsge.offset += start; > + rsge.offset += start - offset; > > sk_msg_iter_var_next(i); > sg_unmark_end(psge);
