Hi,
the referenced syzbot issue has already been fixed in upstream here:
https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/?id=5f33a09e769a9da0482f20a6770a342842443776
("can: isotp: convert struct tpcon::{idx,len} to unsigned int")
Additionally this fix changes some behaviour that is required by the ISO
16765-2 specification (see below).
On 17.01.22 13:01, Ziyang Xuan wrote:
When receive a FF, the current code logic does not consider the real
so->rx.state but set so->rx.state to ISOTP_IDLE directly. That will
make so->rx accessed by multiple receiving processes concurrently.
This is intentionally. "multiple receiving processes" are not allowed
resp. specified by ISO 15765-2.
The following syz problem is one of the scenarios. so->rx.len is
changed by isotp_rcv_ff() during isotp_rcv_cf(), so->rx.len equals
0 before alloc_skb() and equals 4096 after alloc_skb(). That will
trigger skb_over_panic() in skb_put().
=======================================================
CPU: 1 PID: 19 Comm: ksoftirqd/1 Not tainted 5.16.0-rc8-syzkaller #0
RIP: 0010:skb_panic+0x16c/0x16e net/core/skbuff.c:113
Call Trace:
<TASK>
skb_over_panic net/core/skbuff.c:118 [inline]
skb_put.cold+0x24/0x24 net/core/skbuff.c:1990
isotp_rcv_cf net/can/isotp.c:570 [inline]
isotp_rcv+0xa38/0x1e30 net/can/isotp.c:668
deliver net/can/af_can.c:574 [inline]
can_rcv_filter+0x445/0x8d0 net/can/af_can.c:635
can_receive+0x31d/0x580 net/can/af_can.c:665
can_rcv+0x120/0x1c0 net/can/af_can.c:696
__netif_receive_skb_one_core+0x114/0x180 net/core/dev.c:5465
__netif_receive_skb+0x24/0x1b0 net/core/dev.c:5579
Check so->rx.state equals ISOTP_IDLE firstly in isotp_rcv_ff().
Make sure so->rx idle when receive another new packet. And set
so->rx.state to ISOTP_IDLE after whole packet being received.
Fixes: e057dd3fc20f ("can: add ISO 15765-2:2016 transport protocol")
Reported-by: syzbot+4c63f36709a642f801c5@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ziyang Xuan <william.xuanziyang@xxxxxxxxxx>
---
net/can/isotp.c | 28 +++++++++++++++++-----------
1 file changed, 17 insertions(+), 11 deletions(-)
diff --git a/net/can/isotp.c b/net/can/isotp.c
index df6968b28bf4..a4b174f860f3 100644
--- a/net/can/isotp.c
+++ b/net/can/isotp.c
@@ -443,8 +443,10 @@ static int isotp_rcv_ff(struct sock *sk, struct canfd_frame *cf, int ae)
int off;
int ff_pci_sz;
+ if (so->rx.state != ISOTP_IDLE)
+ return 0;
+
hrtimer_cancel(&so->rxtimer);
- so->rx.state = ISOTP_IDLE;
No matter in which receiving state we receive a first frame (FF) we are
required to start a fresh reception process and/or terminate the current
attempt.
Best regards,
Oliver
/* get the used sender LL_DL from the (first) CAN frame data length */
so->rx.ll_dl = padlen(cf->len);
@@ -518,8 +520,6 @@ static int isotp_rcv_cf(struct sock *sk, struct canfd_frame *cf, int ae,
so->lastrxcf_tstamp = skb->tstamp;
}
- hrtimer_cancel(&so->rxtimer);
-
/* CFs are never longer than the FF */
if (cf->len > so->rx.ll_dl)
return 1;
@@ -531,15 +531,15 @@ static int isotp_rcv_cf(struct sock *sk, struct canfd_frame *cf, int ae,
return 1;
}
+ hrtimer_cancel(&so->rxtimer);
+
if ((cf->data[ae] & 0x0F) != so->rx.sn) {
/* wrong sn detected - report 'illegal byte sequence' */
sk->sk_err = EILSEQ;
if (!sock_flag(sk, SOCK_DEAD))
sk_error_report(sk);
- /* reset rx state */
- so->rx.state = ISOTP_IDLE;
- return 1;
+ goto err_out;
}
so->rx.sn++;
so->rx.sn %= 16;
@@ -551,21 +551,18 @@ static int isotp_rcv_cf(struct sock *sk, struct canfd_frame *cf, int ae,
}
if (so->rx.idx >= so->rx.len) {
- /* we are done */
- so->rx.state = ISOTP_IDLE;
-
if ((so->opt.flags & ISOTP_CHECK_PADDING) &&
check_pad(so, cf, i + 1, so->opt.rxpad_content)) {
/* malformed PDU - report 'not a data message' */
sk->sk_err = EBADMSG;
if (!sock_flag(sk, SOCK_DEAD))
sk_error_report(sk);
- return 1;
+ goto err_out;
}
nskb = alloc_skb(so->rx.len, gfp_any());
if (!nskb)
- return 1;
+ goto err_out;
memcpy(skb_put(nskb, so->rx.len), so->rx.buf,
so->rx.len);
@@ -573,6 +570,10 @@ static int isotp_rcv_cf(struct sock *sk, struct canfd_frame *cf, int ae,
nskb->tstamp = skb->tstamp;
nskb->dev = skb->dev;
isotp_rcv_skb(nskb, sk);
+
+ /* we are done */
+ so->rx.state = ISOTP_IDLE;
+
return 0;
}
@@ -591,6 +592,11 @@ static int isotp_rcv_cf(struct sock *sk, struct canfd_frame *cf, int ae,
/* we reached the specified blocksize so->rxfc.bs */
isotp_send_fc(sk, ae, ISOTP_FC_CTS);
return 0;
+
+err_out:
+ /* reset rx state */
+ so->rx.state = ISOTP_IDLE;
+ return 1;
}
static void isotp_rcv(struct sk_buff *skb, void *data)
