Messages in this thread Patch in this message | | | Subject | Re: [syzbot] general protection fault in smc_tx_sendmsg | From | Guvenc Gulce <> | Date | Mon, 21 Jun 2021 19:18:56 +0200 |
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On 21/06/2021 16:56, Pavel Skripkin wrote: > On Sun, 20 Jun 2021 16:22:16 -0700 > syzbot <syzbot+5dda108b672b54141857@syzkaller.appspotmail.com> wrote: > >> Hello, >> >> syzbot found the following issue on: >> >> HEAD commit: 0c337952 Merge tag 'wireless-drivers-next-2021-06-16' >> of g.. git tree: net-next >> console output: >> https://syzkaller.appspot.com/x/log.txt?x=1621de10300000 kernel >> config: https://syzkaller.appspot.com/x/.config?x=a6380da8984033f1 >> dashboard link: >> https://syzkaller.appspot.com/bug?extid=5dda108b672b54141857 syz >> repro: >> https://syzkaller.appspot.com/x/repro.syz?x=121d2d20300000 C >> reproducer: https://syzkaller.appspot.com/x/repro.c?x=100bd768300000 >> >> The issue was bisected to: >> >> commit f9006acc8dfe59e25aa75729728ac57a8d84fc32 >> Author: Florian Westphal <fw@strlen.de> >> Date: Wed Apr 21 07:51:08 2021 +0000 >> >> netfilter: arp_tables: pass table pointer via nf_hook_ops >> > I think, bisection is wrong this time :) > > It should be e0e4b8fa533858532f1b9ea9c6a4660d09beb37a ("net/smc: Add SMC > statistics support") > > > Some debug results: > > syzkaller repro just opens the socket and calls sendmsg. Ftrace log: > > > 0) | smc_create() { > 0) | smc_sock_alloc() { > 0) + 88.493 us | smc_hash_sk(); > 0) ! 131.487 us | } > 0) ! 189.912 us | } > 0) | smc_sendmsg() { > 0) 2.808 us | smc_tx_sendmsg(); > 0) ! 148.484 us | } > > > That means, that smc_buf_create() wasn't called at all, so we need to > check sndbuf_desc before dereferencing > > Something like this should work > > diff --git a/net/smc/smc_tx.c b/net/smc/smc_tx.c > index 075c4f4b4..e24071b12 100644 > --- a/net/smc/smc_tx.c > +++ b/net/smc/smc_tx.c > @@ -154,7 +154,7 @@ int smc_tx_sendmsg(struct smc_sock *smc, struct msghdr *msg, size_t len) > goto out_err; > } > > - if (len > conn->sndbuf_desc->len) > + if (conn->sndbuf_desc && len > conn->sndbuf_desc->len) > SMC_STAT_RMB_TX_SIZE_SMALL(smc, !conn->lnk); > > if (len > conn->peer_rmbe_size) > > > Thoughts? > > > +CC Guvenc Gulce > > > With regards, > Pavel Skripkin
Thanks for analyzing the cause. Your approach would work but I would prefer that we check the state of the socket before doing the statistics relevant if check. This will ensure that smc_buf_create() was already called. I am testing the fix at the moment which would look like the following:
diff --git a/net/smc/smc_tx.c b/net/smc/smc_tx.c index 075c4f4b41cf..289025cd545a 100644 --- a/net/smc/smc_tx.c +++ b/net/smc/smc_tx.c @@ -154,6 +154,9 @@ int smc_tx_sendmsg(struct smc_sock *smc, struct msghdr *msg, size_t len) goto out_err; }
+ if (sk->sk_state == SMC_INIT) + return -ENOTCONN; + if (len > conn->sndbuf_desc->len) SMC_STAT_RMB_TX_SIZE_SMALL(smc, !conn->lnk);
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