> On 18.01.22 13:46, Ziyang Xuan (William) wrote: >>> 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. >> >> Does it can be a network attack? > > Yes. You can see it like this. The ISO 15765-2 protocol is an unreliable UDP-like datagram protocol and the session layer takes care about timeouts and packet lost. > > If you want to disturb that protocol you can also send PDUs with out-of-sync packet counters which will make the receiver drop the communication attempt. > > This is 'CAN-style' ... as usually the bus is very reliable. Security and reliable communication is done on top of these protocols. > >> It receives packets from network, but unexpected packets order make server panic. > > Haha, no :-) > > Unexpected packets should not make the server panic but only drop the communication process. 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]; 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 [ 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! > In the case pointed out by syzbot the unsigned 32 bit length information was stored in a signed 32 bit integer which caused a sanity check to fail. > > This is now fixed with the patch from Marc. > > Regards, > Oliver > .
