Re: [syzbot] net-next boot error: WARNING: refcount bug in fib_create_info
From: Jakub Kicinski <kuba@kernel.org>
Date: 2021-08-03 21:04:39
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On Tue, 3 Aug 2021 19:31:50 +0300 Pavel Skripkin wrote:
On 8/3/21 7:12 PM, Pavel Skripkin wrote:quoted
On 8/3/21 7:07 PM, syzbot wrote:quoted
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:1554Missed refcount_set(), I thinkdiff --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 */
Why 0? ofi is an existing object it's already initialized.
quoted hunk ↗ jump to hunk
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?