Re: [PATCH] ppp: Prevent out-of-bounds access in ppp_sync_txmunge
Purva Yeshi <[email protected]>
| Newsgroups | gmane.linux.ppp,gmane.linux.kernel,gmane.linux.network |
|---|---|
| Message-ID | <[email protected]> |
On 18/02/25 02:46, Kuniyuki Iwashima wrote: > From: Purva Yeshi <[email protected]> > 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: [email protected] >> Closes: https://syzkaller.appspot.com/bug?extid=29fc8991b0ecb186cf40 >> Tested-by: [email protected] >> Signed-off-by: Purva Yeshi <[email protected]> >> --- >> 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 ? skb pointer can be NULL in cases where memory allocation for the socket buffer fails, or if an upstream function incorrectly passes a NULL reference due to improper error handling. Additionally, skb->len being less than 3 can occur if the received packet is truncated or malformed, leading to out-of-bounds memory access when attempting to read data[2]. > > >> + kfree_skb(skb); >> + return NULL; >> + } >> + >> data = skb->data; >> proto = get_unaligned_be16(data); >> >> -- >> 2.34.1