Messages in this thread | | | Date | Thu, 20 Jan 2022 15:46:13 +0100 | Subject | Re: [PATCH net] can: isotp: isotp_rcv_cf(): fix so->rx race problem | From | Oliver Hartkopp <> |
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On 20.01.22 12:28, Ziyang Xuan (William) wrote: >> >> On 20.01.22 07:24, Ziyang Xuan (William) wrote: >> >>> I have reproduced the syz problem with Marc's commit, the commit can not fix the panic problem. >>> So I tried to find the root cause for panic and gave my solution. >>> >>> Marc's commit just fix the condition that packet size bigger than INT_MAX which trigger >>> tpcon::{idx,len} integer overflow, but the packet size is 4096 in the syz problem. >>> >>> so->rx.len is 0 after the following logic in isotp_rcv_ff(): >>> >>> /* get the FF_DL */ >>> so->rx.len = (cf->data[ae] & 0x0F) << 8; >>> so->rx.len += cf->data[ae + 1]; >>> >>> so->rx.len is 4096 after the following logic in isotp_rcv_ff(): >>> >>> /* FF_DL = 0 => get real length from next 4 bytes */ >>> so->rx.len = cf->data[ae + 2] << 24; >>> so->rx.len += cf->data[ae + 3] << 16; >>> so->rx.len += cf->data[ae + 4] << 8; >>> so->rx.len += cf->data[ae + 5]; >>> >> >> In these cases the values 0 could be the minimum value in so->rx.len - but e.g. the value 0 can not show up in isotp_rcv_cf() as this function requires so->rx.state to be ISOTP_WAIT_DATA. > > Consider the scenario that isotp_rcv_cf() and isotp_rcv_cf() are concurrent for the same isotp_sock as following sequence:
o_O
Sorry but the receive path is not designed to handle concurrent receptions that would run isotp_rcv_cf() and isotp_rcv_ff() simultaneously.
> isotp_rcv_cf() > if (so->rx.state != ISOTP_WAIT_DATA) [false] > isotp_rcv_ff() > so->rx.state = ISOTP_IDLE > /* get the FF_DL */ [so->rx.len == 0] > alloc_skb() [so->rx.len == 0] > /* FF_DL = 0 => get real length from next 4 bytes */ [so->rx.len == 4096] > skb_put(nskb, so->rx.len) [so->rx.len == 4096] > skb_over_panic() >
Even though this case is not possible with a real CAN bus due to the CAN frame transmission times we could introduce some locking (or dropping of concurrent CAN frames) in isotp_rcv() - but this code runs in net softirq context ...
Regards, Oliver
>> >> And when so->rx.len is 0 in isotp_rcv_ff() this check >> >> if (so->rx.len + ae + off + ff_pci_sz < so->rx.ll_dl) >> return 1; >> >> will return from isotp_rcv_ff() before ISOTP_WAIT_DATA is set at the end. So after that above check we are still in ISOTP_IDLE state. >> >> Or did I miss something here? >> >>> so->rx.len is 0 before alloc_skb() and is 4096 after alloc_skb() in isotp_rcv_cf(). The following >>> skb_put() will trigger panic. >>> >>> The following log is my reproducing log with Marc's commit and my debug modification in isotp_rcv_cf(). >>> >>> [ 150.605776][ C6] isotp_rcv_cf: before alloc_skb so->rc.len: 0, after alloc_skb so->rx.len: 4096 >> >> >> But so->rx_len is not a value that is modified by alloc_skb(): >> >> nskb = alloc_skb(so->rx.len, gfp_any()); >> if (!nskb) >> return 1; >> >> memcpy(skb_put(nskb, so->rx.len), so->rx.buf, >> so->rx.len); >> >> >> Can you send your debug modification changes please? > > My reproducing debug as attachment and following: > > diff --git a/net/can/isotp.c b/net/can/isotp.c > index df6968b28bf4..8b12d63b4d59 100644 > --- a/net/can/isotp.c > +++ b/net/can/isotp.c > @@ -119,8 +119,8 @@ enum { > }; > > struct tpcon { > - int idx; > - int len; > + unsigned int idx; > + unsigned int len; > u32 state; > u8 bs; > u8 sn; > @@ -505,6 +505,7 @@ static int isotp_rcv_cf(struct sock *sk, struct canfd_frame *cf, int ae, > struct isotp_sock *so = isotp_sk(sk); > struct sk_buff *nskb; > int i; > + bool unexpection = false; > > if (so->rx.state != ISOTP_WAIT_DATA) > return 0; > @@ -562,11 +563,13 @@ static int isotp_rcv_cf(struct sock *sk, struct canfd_frame *cf, int ae, > sk_error_report(sk); > return 1; > } > - > + if (so->rx.len == 0) > + unexpection = true; > nskb = alloc_skb(so->rx.len, gfp_any()); > if (!nskb) > return 1; > - > + if (unexpection) > + printk("%s: before alloc_skb so->rc.len: 0, after alloc_skb so->rx.len: %u\n", __func__, so->rx.len); > memcpy(skb_put(nskb, so->rx.len), so->rx.buf, > so->rx.len); > > >> >> Best regards, >> Oliver >> >>> [ 150.611477][ C6] skbuff: skb_over_panic: text:ffffffff881ff7be len:4096 put:4096 head:ffff88807f93a800 data:ffff88807f93a800 tail:0x1000 end:0xc0 dev:<NULL> >>> [ 150.615837][ C6] ------------[ cut here ]------------ >>> [ 150.617238][ C6] kernel BUG at net/core/skbuff.c:113! >>> >> >> .
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