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Subject: Re: [syzbot] net-next boot error: WARNING: refcount bug in
 fib_create_info
To:     syzbot <syzbot+c5ac86461673ef58847c@syzkaller.appspotmail.com>,
        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>
From:   Pavel Skripkin <paskripkin@gmail.com>
Message-ID: <02372175-c3a1-3f8e-28fe-66d812f4c612@gmail.com>
Date:   Tue, 3 Aug 2021 19:12:54 +0300
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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 <syzkaller>.
> ------------[ 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;


With regards,
Pavel Skripkin