On Sun, 20 Jun 2021 16:22:16 -0700 syzbot <syzbot+5dda108b672b54141857@xxxxxxxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxx> > 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
