Re: [PATCH net] can: isotp: isotp_rcv_cf(): fix so->rx race problem
From: Oliver Hartkopp <socketcan@hartkopp.net>
Date: 2022-01-18 08:04:23
Also in:
linux-can, lkml
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.
quoted hunk ↗ jump to hunk
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@syzkaller.appspotmail.com Signed-off-by: Ziyang Xuan <redacted> --- 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
quoted hunk ↗ jump to hunk
/* 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)