From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: MIME-Version: 1.0 In-Reply-To: References: <001a113f6736499d1c0566363863@google.com> <201803041457.GBJ69774.OVOSOLFHQMJFFt@I-love.SAKURA.ne.jp> <201804012011.ABI74044.MJtOFVSHFQFOOL@I-love.SAKURA.ne.jp> From: Dmitry Vyukov Date: Sun, 1 Apr 2018 13:50:01 +0200 Message-ID: Subject: Re: WARNING: refcount bug in should_fail To: Tetsuo Handa Cc: Al Viro , "Eric W. Biederman" , linux-fsdevel , netdev , Linux-MM , syzkaller-bugs@googlegroups.com, syzbot+84371b6062cb639d797e@syzkaller.appspotmail.com Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: On Sun, Apr 1, 2018 at 1:46 PM, Dmitry Vyukov wrote: > On Sun, Apr 1, 2018 at 1:30 PM, Dmitry Vyukov wrote: >> On Sun, Apr 1, 2018 at 1:11 PM, Tetsuo Handa >> wrote: >>> Dmitry Vyukov wrote: >>>> On Sun, Apr 1, 2018 at 12:32 PM, Dmitry Vyukov wrote: >>>> > On Sun, Mar 4, 2018 at 6:57 AM, Tetsuo Handa >>>> > wrote: >>>> >> Switching from mm to fsdevel, for this report says that put_net(net) in >>>> >> rpc_kill_sb() made net->count < 0 when mount_ns() failed due to >>>> >> register_shrinker() failure. >>>> >> >>>> >> Relevant commits will be >>>> >> commit 9ee332d99e4d5a97 ("sget(): handle failures of register_shrinker()") and >>>> >> commit d91ee87d8d85a080 ("vfs: Pass data, ns, and ns->userns to mount_ns."). >>>> >> >>>> >> When sget_userns() in mount_ns() failed, mount_ns() returns an error code to >>>> >> the caller without calling fill_super(). That is, get_net(sb->s_fs_info) was >>>> >> not called by rpc_fill_super() (via fill_super callback passed to mount_ns()) >>>> >> but put_net(sb->s_fs_info) is called by rpc_kill_sb() (via fs->kill_sb() from >>>> >> deactivate_locked_super()). >>>> >> >>>> >> ---------- >>>> >> static struct dentry * >>>> >> rpc_mount(struct file_system_type *fs_type, >>>> >> int flags, const char *dev_name, void *data) >>>> >> { >>>> >> struct net *net = current->nsproxy->net_ns; >>>> >> return mount_ns(fs_type, flags, data, net, net->user_ns, rpc_fill_super); >>>> >> } >>>> >> ---------- >>>> > >>>> > Messed kernel output, this is definitely not in should_fail. >>>> > >>>> > #syz dup: WARNING: refcount bug in sk_alloc >>>> >>>> Please don't drop reporter (syzbot) email from CC. >>>> >>>> #syz dup: WARNING: refcount bug in sk_alloc >>>> >>> >>> Excuse me? This "refcount bug in should_fail" is talking about sget_userns() versus rpc_fill_super(). >>> I think we need to fix either 9ee332d99e4d5a97 or d91ee87d8d85a080. >> >> Hi, >> >> I think I was looking at this incarnation of this bug before marking it as dup: >> https://syzkaller.appspot.com/text?tag=CrashReport&id=5246446760624128 >> that report in fact includes sk_alloc frame. Kernel turning crash >> reports into untangleable mess is not really helpful. >> >> I will undup this into an independent bug. >> It's just that we don't have such functionality yet, so I need to >> implement it first. > > This is now implemented: > https://github.com/google/syzkaller/commit/0a78e248b7b6537ccdf66dc8806d76e0a97efe21 > Let's try it: > > #syz undup OK, this is now a separate bug again: https://syzkaller.appspot.com/bug?id=55c7257f74dd17f65a9d057b316c46d156b0fba4 The last step is that somebody needs to actually fix it (until too many different bugs pile up under "WARNING: refcount bug in should_fail") ;) >>>> >> syzbot wrote: >>>> >>> Hello, >>>> >>> >>>> >>> syzbot hit the following crash on bpf-next commit >>>> >>> 6f1b5a2b58d8470e5a8b25ab29f5fdb4616ffff8 (Tue Feb 27 04:11:23 2018 +0000) >>>> >>> Merge branch 'bpf-kselftest-improvements' >>>> >>> >>>> >>> C reproducer is attached. >>>> >>> syzkaller reproducer is attached. >>>> >>> Raw console output is attached. >>>> >>> compiler: gcc (GCC) 7.1.1 20170620 >>>> >>> .config is attached. >>>> >>> >>>> >>> IMPORTANT: if you fix the bug, please add the following tag to the commit: >>>> >>> Reported-by: syzbot+84371b6062cb639d797e@syzkaller.appspotmail.com >>>> >>> It will help syzbot understand when the bug is fixed. See footer for >>>> >>> details. >>>> >>> If you forward the report, please keep this part and the footer. >>>> >>> >>>> >>> ------------[ cut here ]------------ >>>> >>> FAULT_INJECTION: forcing a failure. >>>> >>> name failslab, interval 1, probability 0, space 0, times 0 >>>> >>> refcount_t: underflow; use-after-free. >>>> >>> CPU: 1 PID: 4239 Comm: syzkaller149381 Not tainted 4.16.0-rc2+ #20 >>>> >>> WARNING: CPU: 0 PID: 4237 at lib/refcount.c:187 >>>> >>> refcount_sub_and_test+0x167/0x1b0 lib/refcount.c:187 >>>> >>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS >>>> >>> Google 01/01/2011 >>>> >>> Call Trace: >>>> >>> Kernel panic - not syncing: panic_on_warn set ... >>>> >>> >>>> >>> __dump_stack lib/dump_stack.c:17 [inline] >>>> >>> dump_stack+0x194/0x24d lib/dump_stack.c:53 >>>> >>> fail_dump lib/fault-inject.c:51 [inline] >>>> >>> should_fail+0x8c0/0xa40 lib/fault-inject.c:149 >>>> >>> should_failslab+0xec/0x120 mm/failslab.c:32 >>>> >>> slab_pre_alloc_hook mm/slab.h:422 [inline] >>>> >>> slab_alloc mm/slab.c:3365 [inline] >>>> >>> __do_kmalloc mm/slab.c:3703 [inline] >>>> >>> __kmalloc+0x63/0x760 mm/slab.c:3714 >>>> >>> kmalloc include/linux/slab.h:517 [inline] >>>> >>> kzalloc include/linux/slab.h:701 [inline] >>>> >>> register_shrinker+0x10e/0x2d0 mm/vmscan.c:268 >>>> >>> sget_userns+0xbbf/0xe40 fs/super.c:520 >>>> >>> mount_ns+0x6d/0x190 fs/super.c:1029 >>>> >>> rpc_mount+0x9e/0xd0 net/sunrpc/rpc_pipe.c:1451 >>>> >>> mount_fs+0x66/0x2d0 fs/super.c:1222 >>>> >>> vfs_kern_mount.part.26+0xc6/0x4a0 fs/namespace.c:1037 >>>> >>> vfs_kern_mount fs/namespace.c:2509 [inline] >>>> >>> do_new_mount fs/namespace.c:2512 [inline] >>>> >>> do_mount+0xea4/0x2bb0 fs/namespace.c:2842 >>>> >>> SYSC_mount fs/namespace.c:3058 [inline] >>>> >>> SyS_mount+0xab/0x120 fs/namespace.c:3035 >>>> >>> do_syscall_64+0x280/0x940 arch/x86/entry/common.c:287 >>>> >>> entry_SYSCALL_64_after_hwframe+0x42/0xb7 >>>> >>> RIP: 0033:0x4460f9 >>>> >>> RSP: 002b:00007fbcd769ad78 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5 >>>> >>> RAX: ffffffffffffffda RBX: 00000000006dcc6c RCX: 00000000004460f9 >>>> >>> RDX: 0000000020000080 RSI: 0000000020000040 RDI: 0000000020000000 >>>> >>> RBP: 00007fbcd769ad80 R08: 00000000200000c0 R09: 0000000000003131 >>>> >>> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dcc68 >>>> >>> R13: ffffffffffffffff R14: 0000000000000037 R15: 0030656c69662f2e >>>> >>> CPU: 0 PID: 4237 Comm: syzkaller149381 Not tainted 4.16.0-rc2+ #20 >>>> >>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS >>>> >>> Google 01/01/2011 >>>> >>> Call Trace: >>>> >>> __dump_stack lib/dump_stack.c:17 [inline] >>>> >>> dump_stack+0x194/0x24d lib/dump_stack.c:53 >>>> >>> panic+0x1e4/0x41c kernel/panic.c:183 >>>> >>> __warn+0x1dc/0x200 kernel/panic.c:547 >>>> >>> report_bug+0x211/0x2d0 lib/bug.c:184 >>>> >>> fixup_bug.part.11+0x37/0x80 arch/x86/kernel/traps.c:178 >>>> >>> fixup_bug arch/x86/kernel/traps.c:247 [inline] >>>> >>> do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:296 >>>> >>> do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315 >>>> >>> invalid_op+0x58/0x80 arch/x86/entry/entry_64.S:957 >>>> >>> RIP: 0010:refcount_sub_and_test+0x167/0x1b0 lib/refcount.c:187 >>>> >>> RSP: 0018:ffff8801b164f6d8 EFLAGS: 00010286 >>>> >>> RAX: dffffc0000000008 RBX: 0000000000000000 RCX: ffffffff815ac30e >>>> >>> RDX: 0000000000000000 RSI: 1ffff100362c9e8b RDI: 1ffff100362c9e60 >>>> >>> RBP: ffff8801b164f768 R08: 0000000000000000 R09: 0000000000000000 >>>> >>> R10: ffff8801b164f610 R11: 0000000000000000 R12: 1ffff100362c9edc >>>> >>> R13: 00000000ffffffff R14: 0000000000000001 R15: ffff8801ae924044 >>>> >>> refcount_dec_and_test+0x1a/0x20 lib/refcount.c:212 >>>> >>> put_net include/net/net_namespace.h:220 [inline] >>>> >>> rpc_kill_sb+0x253/0x3c0 net/sunrpc/rpc_pipe.c:1473 >>>> >>> deactivate_locked_super+0x88/0xd0 fs/super.c:312 >>>> >>> sget_userns+0xbda/0xe40 fs/super.c:522 >>>> >>> mount_ns+0x6d/0x190 fs/super.c:1029 >>>> >>> rpc_mount+0x9e/0xd0 net/sunrpc/rpc_pipe.c:1451 >>>> >>> mount_fs+0x66/0x2d0 fs/super.c:1222 >>>> >>> vfs_kern_mount.part.26+0xc6/0x4a0 fs/namespace.c:1037 >>>> >>> vfs_kern_mount fs/namespace.c:2509 [inline] >>>> >>> do_new_mount fs/namespace.c:2512 [inline] >>>> >>> do_mount+0xea4/0x2bb0 fs/namespace.c:2842 >>>> >>> SYSC_mount fs/namespace.c:3058 [inline] >>>> >>> SyS_mount+0xab/0x120 fs/namespace.c:3035 >>>> >>> do_syscall_64+0x280/0x940 arch/x86/entry/common.c:287 >>>> >>> entry_SYSCALL_64_after_hwframe+0x42/0xb7 >>>> >>> RIP: 0033:0x4460f9 >>>> >>> RSP: 002b:00007fbcd76dcd78 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5 >>>> >>> RAX: ffffffffffffffda RBX: 00000000006dcc3c RCX: 00000000004460f9 >>>> >>> RDX: 0000000020000080 RSI: 0000000020000040 RDI: 0000000020000000 >>>> >>> RBP: 00007fbcd76dcd80 R08: 00000000200000c0 R09: 0000000000003131 >>>> >>> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dcc38 >>>> >>> R13: ffffffffffffffff R14: 0000000000000028 R15: 0030656c69662f2e >>>> >>> Dumping ftrace buffer: >>>> >>> (ftrace buffer empty) >>>> >>> Kernel Offset: disabled >>>> >>> Rebooting in 86400 seconds.. >>>> >>> >>>> >>> >>>> >>> --- >>>> >>> This bug is generated by a dumb bot. It may contain errors. >>>> >>> See https://goo.gl/tpsmEJ for details. >>>> >>> Direct all questions to syzkaller@googlegroups.com. >>>> >>> >>>> >>> syzbot will keep track of this bug report. >>>> >>> If you forgot to add the Reported-by tag, once the fix for this bug is >>>> >>> merged >>>> >>> into any tree, please reply to this email with: >>>> >>> #syz fix: exact-commit-title >>>> >>> If you want to test a patch for this bug, please reply with: >>>> >>> #syz test: git://repo/address.git branch >>>> >>> and provide the patch inline or as an attachment. >>>> >>> To mark this as a duplicate of another syzbot report, please reply with: >>>> >>> #syz dup: exact-subject-of-another-report >>>> >>> If it's a one-off invalid bug report, please reply with: >>>> >>> #syz invalid >>>> >>> Note: if the crash happens again, it will cause creation of a new bug >>>> >>> report. >>>> >>> Note: all commands must start from beginning of the line in the email body. >>>> >>> >>>> >> >>>> >> -- >>>> >> You received this message because you are subscribed to the Google Groups "syzkaller-bugs" group. >>>> >> To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller-bugs+unsubscribe@googlegroups.com. >>>> >> To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/201803041457.GBJ69774.OVOSOLFHQMJFFt%40I-love.SAKURA.ne.jp. >>>> >> For more options, visit https://groups.google.com/d/optout. >>>> >>> >>> -- >>> You received this message because you are subscribed to the Google Groups "syzkaller-bugs" group. >>> To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller-bugs+unsubscribe@googlegroups.com. >>> To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/201804012011.ABI74044.MJtOFVSHFQFOOL%40I-love.SAKURA.ne.jp. >>> For more options, visit https://groups.google.com/d/optout.