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Tue, 03 Aug 2021 09:31:51 -0700 (PDT) Subject: Re: [syzbot] net-next boot error: WARNING: refcount bug in fib_create_info From: Pavel Skripkin To: syzbot , davem@davemloft.net, dsahern@kernel.org, kuba@kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, syzkaller-bugs@googlegroups.com, yoshfuji@linux-ipv6.org References: <0000000000005e090405c8a9e1c3@google.com> <02372175-c3a1-3f8e-28fe-66d812f4c612@gmail.com> Message-ID: Date: Tue, 3 Aug 2021 19:31:50 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <02372175-c3a1-3f8e-28fe-66d812f4c612@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/3/21 7:12 PM, Pavel Skripkin wrote: > On 8/3/21 7:07 PM, syzbot wrote: >> Hello, >> >> syzbot found the following issue on: >> >> HEAD commit: 1187c8c4642d net: phy: mscc: make some arrays static const.. >> git tree: net-next >> console output: https://syzkaller.appspot.com/x/log.txt?x=140e7b3e300000 >> kernel config: https://syzkaller.appspot.com/x/.config?x=f9bb42efdc6f1d7 >> dashboard link: https://syzkaller.appspot.com/bug?extid=c5ac86461673ef58847c >> compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.1 >> >> IMPORTANT: if you fix the issue, please add the following tag to the commit: >> Reported-by: syzbot+c5ac86461673ef58847c@syzkaller.appspotmail.com >> >> FS-Cache: Netfs 'afs' registered for caching >> Btrfs loaded, crc32c=crc32c-intel, assert=on, zoned=yes >> Key type big_key registered >> Key type encrypted registered >> AppArmor: AppArmor sha1 policy hashing enabled >> ima: No TPM chip found, activating TPM-bypass! >> Loading compiled-in module X.509 certificates >> Loaded X.509 cert 'Build time autogenerated kernel key: f850c787ad998c396ae089c083b940ff0a9abb77' >> ima: Allocated hash algorithm: sha256 >> ima: No architecture policies found >> evm: Initialising EVM extended attributes: >> evm: security.selinux (disabled) >> evm: security.SMACK64 (disabled) >> evm: security.SMACK64EXEC (disabled) >> evm: security.SMACK64TRANSMUTE (disabled) >> evm: security.SMACK64MMAP (disabled) >> evm: security.apparmor >> evm: security.ima >> evm: security.capability >> evm: HMAC attrs: 0x1 >> PM: Magic number: 1:990:690 >> printk: console [netcon0] enabled >> netconsole: network logging started >> gtp: GTP module loaded (pdp ctx size 104 bytes) >> rdma_rxe: loaded >> cfg80211: Loading compiled-in X.509 certificates for regulatory database >> cfg80211: Loaded X.509 cert 'sforshee: 00b28ddf47aef9cea7' >> ALSA device list: >> #0: Dummy 1 >> #1: Loopback 1 >> #2: Virtual MIDI Card 1 >> md: Waiting for all devices to be available before autodetect >> md: If you don't use raid, use raid=noautodetect >> md: Autodetecting RAID arrays. >> md: autorun ... >> md: ... autorun DONE. >> EXT4-fs (sda1): mounted filesystem without journal. Opts: (null). Quota mode: none. >> VFS: Mounted root (ext4 filesystem) readonly on device 8:1. >> devtmpfs: mounted >> Freeing unused kernel image (initmem) memory: 4476K >> Write protecting the kernel read-only data: 169984k >> Freeing unused kernel image (text/rodata gap) memory: 2012K >> Freeing unused kernel image (rodata/data gap) memory: 1516K >> Run /sbin/init as init process >> systemd[1]: systemd 232 running in system mode. (+PAM +AUDIT +SELINUX +IMA +APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ +LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD +IDN) >> systemd[1]: Detected virtualization kvm. >> systemd[1]: Detected architecture x86-64. >> systemd[1]: Set hostname to . >> ------------[ cut here ]------------ >> refcount_t: addition on 0; use-after-free. >> WARNING: CPU: 1 PID: 1 at lib/refcount.c:25 refcount_warn_saturate+0x169/0x1e0 lib/refcount.c:25 >> Modules linked in: >> CPU: 1 PID: 1 Comm: systemd Not tainted 5.14.0-rc3-syzkaller #0 >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 >> RIP: 0010:refcount_warn_saturate+0x169/0x1e0 lib/refcount.c:25 >> Code: 09 31 ff 89 de e8 d7 fa 9e fd 84 db 0f 85 36 ff ff ff e8 8a f4 9e fd 48 c7 c7 c0 81 e3 89 c6 05 70 51 81 09 01 e8 48 f8 13 05 <0f> 0b e9 17 ff ff ff e8 6b f4 9e fd 0f b6 1d 55 51 81 09 31 ff 89 >> RSP: 0018:ffffc90000c66ab0 EFLAGS: 00010286 >> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 >> RDX: ffff88813fe48000 RSI: ffffffff815d7b25 RDI: fffff5200018cd48 >> RBP: 0000000000000002 R08: 0000000000000000 R09: 0000000000000001 >> R10: ffffffff815d195e R11: 0000000000000000 R12: 0000000000000004 >> R13: 0000000000000001 R14: 0000000000000000 R15: ffff888027722e00 >> FS: 00007f8c1c5d0500(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000 >> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> CR2: 000055ed0ced4368 CR3: 0000000026bac000 CR4: 00000000001506e0 >> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 >> Call Trace: >> __refcount_add include/linux/refcount.h:199 [inline] >> __refcount_inc include/linux/refcount.h:250 [inline] >> refcount_inc include/linux/refcount.h:267 [inline] >> fib_create_info+0x36af/0x4910 net/ipv4/fib_semantics.c:1554 > > Missed refcount_set(), I think > > diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c > index f29feb7772da..bb9949f6bb70 100644 > --- a/net/ipv4/fib_semantics.c > +++ b/net/ipv4/fib_semantics.c > @@ -1428,6 +1428,7 @@ struct fib_info *fib_create_info(struct fib_config > *cfg, > } > > fib_info_cnt++; > + refcount_set(&fi->fib_treeref, 1); > fi->fib_net = net; > fi->fib_protocol = cfg->fc_protocol; > fi->fib_scope = cfg->fc_scope; > > > > > Oops, it's already fixed in -next, so #syz fix: ipv4: Fix refcount warning for new fib_info BTW: there is one more bug with refcounts: link_it: ofi = fib_find_info(fi); if (ofi) { fi->fib_dead = 1; free_fib_info(fi); refcount_inc(&ofi->fib_treeref); ^^^^^^^^^^^^^^^^^^^^^^^ / *fib_treeref is 0 here */ return ofi; } refcount_set(&fi->fib_treeref, 1); diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c index f29feb7772da..38d1fc4d0be1 100644 --- a/net/ipv4/fib_semantics.c +++ b/net/ipv4/fib_semantics.c @@ -1543,6 +1543,8 @@ struct fib_info *fib_create_info(struct fib_config *cfg, } link_it: + refcount_set(&fi->fib_treeref, 1); + ofi = fib_find_info(fi); if (ofi) { fi->fib_dead = 1; @@ -1551,7 +1553,6 @@ struct fib_info *fib_create_info(struct fib_config *cfg, return ofi; } - refcount_set(&fi->fib_treeref, 1); refcount_set(&fi->fib_clntref, 1); spin_lock_bh(&fib_info_lock); hlist_add_head(&fi->fib_hash, Thoughts? With regards, Pavel Skripkin