On 2018/04/02 2:01, syzbot wrote: > Hello, > > syzbot hit the following crash on bpf-next commit > 7828f20e3779e4e85e55371e0e43f5006a15fb41 (Sat Mar 31 00:17:57 2018 +0000) > Merge branch 'bpf-cgroup-bind-connect' > syzbot dashboard link: https://syzkaller.appspot.com/bug?extid=151de3f2be6b40ac8026 > > So far this crash happened 3 times on bpf-next. > C reproducer: https://syzkaller.appspot.com/x/repro.c?id=4857382450495488 > syzkaller reproducer: https://syzkaller.appspot.com/x/repro.syz?id=4644052230209536 > Raw console output: https://syzkaller.appspot.com/x/log.txt?id=5798498637185024 > Kernel config: https://syzkaller.appspot.com/x/.config?id=5909223872832634926 > compiler: gcc (GCC) 7.1.1 20170620 Al, I think this is another example of crash triggered by commit 9ee332d99e4d5a97 ("sget(): handle failures of register_shrinker()"). ---------------------------------------- [ 23.407545] FAULT_INJECTION: forcing a failure. [ 23.407545] name failslab, interval 1, probability 0, space 0, times 1 [ 23.414735] CPU: 1 PID: 4471 Comm: syzkaller129261 Not tainted 4.16.0-rc6+ #43 [ 23.433147] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 23.442491] Call Trace: [ 23.445074] dump_stack+0x194/0x24d [ 23.448689] ? arch_local_irq_restore+0x53/0x53 [ 23.453347] ? find_held_lock+0x35/0x1d0 [ 23.457401] should_fail+0x8c0/0xa40 [ 23.461100] ? __list_lru_init+0x352/0x750 [ 23.465331] ? fault_create_debugfs_attr+0x1f0/0x1f0 [ 23.470453] ? find_held_lock+0x35/0x1d0 [ 23.474503] ? __lock_is_held+0xb6/0x140 [ 23.478556] ? check_same_owner+0x320/0x320 [ 23.482870] ? rcu_note_context_switch+0x710/0x710 [ 23.487785] ? find_held_lock+0x35/0x1d0 [ 23.491931] should_failslab+0xec/0x120 [ 23.495895] __kmalloc+0x63/0x760 [ 23.499332] ? lock_downgrade+0x980/0x980 [ 23.503469] ? _raw_spin_unlock+0x22/0x30 [ 23.507605] ? register_shrinker+0x10e/0x2d0 [ 23.511999] ? trace_event_raw_event_module_request+0x320/0x320 [ 23.518044] register_shrinker+0x10e/0x2d0 [ 23.522265] ? __bpf_trace_mm_vmscan_wakeup_kswapd+0x40/0x40 [ 23.528051] ? memcpy+0x45/0x50 [ 23.531588] sget_userns+0xbbf/0xe40 [ 23.535296] ? kernfs_sop_show_path+0x190/0x190 [ 23.539959] ? kernfs_sop_show_options+0x180/0x180 [ 23.544876] ? destroy_unused_super.part.6+0xd0/0xd0 [ 23.549972] ? check_same_owner+0x320/0x320 [ 23.554281] ? rcu_pm_notify+0xc0/0xc0 [ 23.558161] ? rcu_read_lock_sched_held+0x108/0x120 [ 23.563168] ? kmem_cache_alloc_trace+0x459/0x740 [ 23.567997] ? lock_downgrade+0x980/0x980 [ 23.572142] kernfs_mount_ns+0x13d/0x8b0 [ 23.576192] ? kernfs_super_ns+0x70/0x70 [ 23.580244] sysfs_mount+0xc2/0x1c0 ---------------------------------------- That commit assumes that calling kill_sb() from deactivate_locked_super(s) without corresponding fill_super() is safe. We have so far crashed with rpc_mount() and kernfs_mount_ns(). Is that really safe? Also, I think ---------------------------------------- struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags, struct kernfs_root *root, unsigned long magic, bool *new_sb_created, const void *ns) { (...snipped...) if (!sb->s_root) { struct kernfs_super_info *info = kernfs_info(sb); error = kernfs_fill_super(sb, magic); if (error) { deactivate_locked_super(sb); // <= this call return ERR_PTR(error); } sb->s_flags |= SB_ACTIVE; mutex_lock(&kernfs_mutex); list_add(&info->node, &root->supers); mutex_unlock(&kernfs_mutex); } (...snipped...) } ---------------------------------------- is not safe, for list_del() is called via kill_sb() without corresponding list_add(). ---------------------------------------- void kernfs_kill_sb(struct super_block *sb) { struct kernfs_super_info *info = kernfs_info(sb); mutex_lock(&kernfs_mutex); list_del(&info->node); // <= NULL pointer dereference mutex_unlock(&kernfs_mutex); /* * Remove the superblock from fs_supers/s_instances * so we can't find it, before freeing kernfs_super_info. */ kill_anon_super(sb); kfree(info); } ---------------------------------------- > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+151de3f2be6b40ac8026@xxxxxxxxxxxxxxxxxxxxxxxxx > 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. > > kasan: GPF could be caused by NULL-ptr deref or user memory access > 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 > general protection fault: 0000 [#1] SMP KASAN > Dumping ftrace buffer: > (ftrace buffer empty) > kmalloc include/linux/slab.h:517 [inline] > kzalloc include/linux/slab.h:701 [inline] > register_shrinker+0x10e/0x2d0 mm/vmscan.c:268 > Modules linked in: > CPU: 1 PID: 4471 Comm: syzkaller129261 Not tainted 4.16.0-rc6+ #43 > sget_userns+0xbbf/0xe40 fs/super.c:520 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > RIP: 0010:__list_del_entry_valid+0x7e/0x150 lib/list_debug.c:51 > RSP: 0018:ffff8801ae017658 EFLAGS: 00010246 > RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000 > RDX: 0000000000000000 RSI: ffff8801d97a6e98 RDI: ffff8801d97a6ea0 > RBP: ffff8801ae017670 R08: ffffffff81d39d22 R09: 0000000000000004 > R10: ffff8801ae017670 R11: 0000000000000000 R12: 0000000000000000 > R13: ffff8801d91dec00 R14: ffff8801ae017700 R15: ffff8801d97a6e98 > FS: 0000000001569880(0000) GS:ffff8801db100000(0000) knlGS:0000000000000000 > kernfs_mount_ns+0x13d/0x8b0 fs/kernfs/mount.c:320 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00000000006d0188 CR3: 00000001da40c005 CR4: 00000000001606e0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > sysfs_mount+0xc2/0x1c0 fs/sysfs/mount.c:36 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > __list_del_entry include/linux/list.h:117 [inline] > list_del include/linux/list.h:125 [inline] > kernfs_kill_sb+0x9e/0x330 fs/kernfs/mount.c:361 > mount_fs+0x66/0x2d0 fs/super.c:1222 > vfs_kern_mount.part.26+0xc6/0x4a0 fs/namespace.c:1037 > sysfs_kill_sb+0x22/0x40 fs/sysfs/mount.c:50 > vfs_kern_mount fs/namespace.c:2509 [inline] > do_new_mount fs/namespace.c:2512 [inline] > do_mount+0xea4/0x2bb0 fs/namespace.c:2842 > deactivate_locked_super+0x88/0xd0 fs/super.c:312 > sget_userns+0xbda/0xe40 fs/super.c:522 > SYSC_mount fs/namespace.c:3058 [inline] > SyS_mount+0xab/0x120 fs/namespace.c:3035 > do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287 > kernfs_mount_ns+0x13d/0x8b0 fs/kernfs/mount.c:320 > sysfs_mount+0xc2/0x1c0 fs/sysfs/mount.c:36 > mount_fs+0x66/0x2d0 fs/super.c:1222 > entry_SYSCALL_64_after_hwframe+0x42/0xb7 > vfs_kern_mount.part.26+0xc6/0x4a0 fs/namespace.c:1037 > RIP: 0033:0x442609 > RSP: 002b:00007fff40a278e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5 > RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000442609 > RDX: 0000000020000140 RSI: 0000000020000040 RDI: 0000000020000000 > RBP: 00007fff40a28190 R08: 00000000200002c0 R09: 0000000300000000 > vfs_kern_mount fs/namespace.c:2509 [inline] > do_new_mount fs/namespace.c:2512 [inline] > do_mount+0xea4/0x2bb0 fs/namespace.c:2842 > R10: 0000000000000000 R11: 0000000000000246 R12: ffffffffffffffff > R13: 0000000000000003 R14: 0000000000001380 R15: 00007fff40a27a28 > SYSC_mount fs/namespace.c:3058 [inline] > SyS_mount+0xab/0x120 fs/namespace.c:3035 > do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287 > entry_SYSCALL_64_after_hwframe+0x42/0xb7 > RIP: 0033:0x442609 > RSP: 002b:00007fff40a278e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5 > RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000442609 > RDX: 0000000020000140 RSI: 0000000020000040 RDI: 0000000020000000 > RBP: 00007fff40a28190 R08: 00000000200002c0 R09: 0000000300000000 > R10: 0000000000000000 R11: 0000000000000246 R12: ffffffffffffffff > R13: 0000000000000003 R14: 0000000000001380 R15: 00007fff40a27a28 > Code: 00 00 00 00 ad de 49 39 c4 74 66 48 b8 00 02 00 00 00 00 ad de 48 89 da 48 39 c3 74 65 48 c1 ea 03 48 b8 00 00 00 00 00 fc ff df <80> 3c 02 00 75 7b 48 8b 13 48 39 f2 75 57 49 8d 7c 24 08 48 b8 > RIP: __list_del_entry_valid+0x7e/0x150 lib/list_debug.c:51 RSP: ffff8801ae017658 > ---[ end trace b14d521943ecadbd ]--- > > > --- > This bug is generated by a dumb bot. It may contain errors. > See https://goo.gl/tpsmEJ for details. > Direct all questions to syzkaller@xxxxxxxxxxxxxxxx. > > 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. >
