| Message ID | 20250216060446.9320-1-purvayeshi550@gmail.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | ppp: Prevent out-of-bounds access in ppp_sync_txmunge | expand |
From: Purva Yeshi <purvayeshi550@gmail.com> 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@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=29fc8991b0ecb186cf40 > Tested-by: syzbot+29fc8991b0ecb186cf40@syzkaller.appspotmail.com > Signed-off-by: Purva Yeshi <purvayeshi550@gmail.com> > --- > 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
On 18/02/25 02:46, Kuniyuki Iwashima wrote: > From: Purva Yeshi <purvayeshi550@gmail.com> > 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@syzkaller.appspotmail.com >> Closes: https://syzkaller.appspot.com/bug?extid=29fc8991b0ecb186cf40 >> Tested-by: syzbot+29fc8991b0ecb186cf40@syzkaller.appspotmail.com >> Signed-off-by: Purva Yeshi <purvayeshi550@gmail.com> >> --- >> 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
From: Purva Yeshi <purvayeshi550@gmail.com> Date: Tue, 18 Feb 2025 11:58:17 +0530 > On 18/02/25 02:46, Kuniyuki Iwashima wrote: > > From: Purva Yeshi <purvayeshi550@gmail.com> > > 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@syzkaller.appspotmail.com > >> Closes: https://syzkaller.appspot.com/bug?extid=29fc8991b0ecb186cf40 > >> Tested-by: syzbot+29fc8991b0ecb186cf40@syzkaller.appspotmail.com > >> Signed-off-by: Purva Yeshi <purvayeshi550@gmail.com> > >> --- > >> 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. Which caller passes NULL skb ? If it's really possible, you'll see null-ptr-deref at data = skb->data; below instead of KMSAN's uninit splat. > > 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
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) { + kfree_skb(skb); + return NULL; + } + data = skb->data; proto = get_unaligned_be16(data);