From: Purva Yeshi <purvayeshi550@xxxxxxxxx> Date: Sun, 16 Feb 2025 11:34:46 +0530 > Fix an issue detected by syzbot with KMSAN: > > BUG: KMSAN: uninit-value in ppp_sync_txmunge > drivers/net/ppp/ppp_synctty.c:516 [inline] > BUG: KMSAN: uninit-value in ppp_sync_send+0x21c/0xb00 > drivers/net/ppp/ppp_synctty.c:568 > > Ensure sk_buff is valid and has at least 3 bytes before accessing its > data field in ppp_sync_txmunge(). Without this check, the function may > attempt to read uninitialized or invalid memory, leading to undefined > behavior. > > To address this, add a validation check at the beginning of the function > to safely handle cases where skb is NULL or too small. If either condition > is met, free the skb and return NULL to prevent processing an invalid > packet. > > Reported-by: syzbot+29fc8991b0ecb186cf40@xxxxxxxxxxxxxxxxxxxxxxxxx > Closes: https://syzkaller.appspot.com/bug?extid=29fc8991b0ecb186cf40 > Tested-by: syzbot+29fc8991b0ecb186cf40@xxxxxxxxxxxxxxxxxxxxxxxxx > Signed-off-by: Purva Yeshi <purvayeshi550@xxxxxxxxx> > --- > drivers/net/ppp/ppp_synctty.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/drivers/net/ppp/ppp_synctty.c b/drivers/net/ppp/ppp_synctty.c > index 644e99fc3..e537ea3d9 100644 > --- a/drivers/net/ppp/ppp_synctty.c > +++ b/drivers/net/ppp/ppp_synctty.c > @@ -506,6 +506,12 @@ ppp_sync_txmunge(struct syncppp *ap, struct sk_buff *skb) > unsigned char *data; > int islcp; > > + /* Ensure skb is not NULL and has at least 3 bytes */ > + if (!skb || skb->len < 3) { When is skb NULL ? > + kfree_skb(skb); > + return NULL; > + } > + > data = skb->data; > proto = get_unaligned_be16(data); > > -- > 2.34.1
