The ppp program adds a 2-byte pseudo-header for socket filters, which is normally skipped by regular BPF programs, causing no issues. However, for abnormal BPF programs that use these uninitialized 2 bytes, a KMSAN warning is triggered. Reported-by: syzbot+853242d9c9917165d791@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://lore.kernel.org/bpf/000000000000dea025060d6bc3bc@xxxxxxxxxx/ Signed-off-by: Jiayuan Chen <jiayuan.chen@xxxxxxxxx> --- drivers/net/ppp/ppp_generic.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c index 4583e15ad03a..a913403d5847 100644 --- a/drivers/net/ppp/ppp_generic.c +++ b/drivers/net/ppp/ppp_generic.c @@ -1765,7 +1765,7 @@ ppp_send_frame(struct ppp *ppp, struct sk_buff *skb) /* check if we should pass this packet */ /* the filter instructions are constructed assuming a four-byte PPP header on each packet */ - *(u8 *)skb_push(skb, 2) = 1; + *(u16 *)skb_push(skb, 2) = 1; if (ppp->pass_filter && bpf_prog_run(ppp->pass_filter, skb) == 0) { if (ppp->debug & 1) @@ -2489,7 +2489,7 @@ ppp_receive_nonmp_frame(struct ppp *ppp, struct sk_buff *skb) if (skb_unclone(skb, GFP_ATOMIC)) goto err; - *(u8 *)skb_push(skb, 2) = 0; + *(u16 *)skb_push(skb, 2) = 0; if (ppp->pass_filter && bpf_prog_run(ppp->pass_filter, skb) == 0) { if (ppp->debug & 1) -- 2.47.1
