Re: WARNING in request_end

Eric W. Biederman
2019-03-23T15:52:27Z

syzbot <syzbot+ef054c4d3f64cd7f7cec@syzkaller.appspotmail.com> writes:

> syzbot has bisected this bug to:

Nope. syzbot got it wrong.

At most that commit will allow a larger class of users to mount fuse
and thus be able to reproduce the problem.

It does look like syzbot has found something concerning though.

Miklos any ideas?

> commit 4ad769f3c346ec3d458e255548dec26ca5284cf6
> Author: Eric W. Biederman <ebiederm@xmission.com>
> Date: Tue May 29 14:04:46 2018 +0000
>
> fuse: Allow fully unprivileged mounts
>
> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=16b4518b200000
> start commit: 0238df64 Linux 4.19-rc7
> git tree: upstream
> final crash: https://syzkaller.appspot.com/x/report.txt?x=15b4518b200000
> console output: https://syzkaller.appspot.com/x/log.txt?x=11b4518b200000
> kernel config: https://syzkaller.appspot.com/x/.config?x=88e9a8a39dc0be2d
> dashboard link: https://syzkaller.appspot.com/bug?extid=ef054c4d3f64cd7f7cec
> userspace arch: i386
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=119bf2e6400000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1760f806400000
>
> Reported-by: syzbot+ef054c4d3f64cd7f7cec@syzkaller.appspotmail.com
> Fixes: 4ad769f3c346 ("fuse: Allow fully unprivileged mounts")
>
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection

From https://syzkaller.appspot.com/x/report.txt?x=15b4518b200000
> [ 448.045793] ==================================================================
> [ 448.053414] BUG: KASAN: use-after-free in fuse_dev_do_read.isra.24+0x166f/0x1be0
> [ 448.060937] Read of size 8 at addr ffff8801cec98430 by task syz-executor0/9001
> [ 448.068286]
> [ 448.069901] CPU: 1 PID: 9001 Comm: syz-executor0 Not tainted 4.16.0-rc6+ #1
> [ 448.076990] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> [ 448.086330] Call Trace:
> [ 448.089107] dump_stack+0x153/0x201
> [ 448.092926] ? arch_local_irq_restore+0x43/0x43
> [ 448.097579] ? printk+0x9a/0xc0
> [ 448.100844] ? show_regs_print_info+0xb/0xb
> [ 448.105265] print_address_description.cold.7+0x9/0x1c9
> [ 448.110739] kasan_report.cold.8+0x242/0x2fe
> [ 448.115255] ? fuse_dev_do_read.isra.24+0x166f/0x1be0
> [ 448.120476] __asan_report_load8_noabort+0x14/0x20
> [ 448.125393] fuse_dev_do_read.isra.24+0x166f/0x1be0
> [ 448.130397] ? debug_check_no_locks_freed+0x310/0x310
> [ 448.135574] ? end_requests+0x470/0x470
> [ 448.139529] ? print_usage_bug+0xc0/0xc0
> [ 448.143576] ? prepare_to_wait+0x4f0/0x4f0
> [ 448.147932] ? print_usage_bug+0xc0/0xc0
> [ 448.152139] ? __unqueue_futex+0x270/0x270
> [ 448.156376] ? add_lock_to_list.isra.29+0x4b0/0x4b0
> [ 448.161703] ? wake_up_q+0x9c/0xe0
> [ 448.165236] ? futex_wake+0x245/0x8a0
> [ 448.169025] ? find_held_lock+0x36/0x1c0
> [ 448.173085] ? aa_file_perm+0x319/0xda0
> [ 448.177065] ? lock_downgrade+0x900/0x900
> [ 448.181241] ? rcu_read_lock_bh_held+0xc0/0xc0
> [ 448.185813] ? debug_smp_processor_id+0x17/0x20
> [ 448.190557] ? rcu_is_watching+0x69/0x180
> [ 448.194700] ? __lock_is_held+0xb5/0x140
> [ 448.198859] ? rcu_dynticks_eqs_exit+0x70/0x70
> [ 448.203436] ? aa_file_perm+0x336/0xda0
> [ 448.207393] ? rcu_read_lock_bh_held+0xc0/0xc0
> [ 448.211958] ? aa_path_link+0x610/0x610
> [ 448.215913] ? rcu_dynticks_eqs_exit+0x70/0x70
> [ 448.220485] ? memset+0x31/0x40
> [ 448.223752] fuse_dev_read+0x185/0x240
> [ 448.227665] ? fuse_dev_splice_read+0x7a0/0x7a0
> [ 448.232375] ? find_held_lock+0x36/0x1c0
> [ 448.236439] __vfs_read+0x54a/0xd20
> [ 448.240161] ? debug_lockdep_rcu_enabled+0x77/0x90
> [ 448.245069] ? vfs_copy_file_range+0xb60/0xb60
> [ 448.249737] ? fsnotify_first_mark+0x280/0x280
> [ 448.254360] ? rw_verify_area+0xb8/0x2b0
> [ 448.258411] ? __fdget_raw+0x10/0x10
> [ 448.262151] vfs_read+0xf5/0x300
> [ 448.265509] SyS_read+0xf5/0x250
> [ 448.268860] ? kernel_write+0x130/0x130
> [ 448.272823] ? do_fast_syscall_32+0x151/0x1016
> [ 448.277396] do_fast_syscall_32+0x3d5/0x1016
> [ 448.281797] ? _raw_spin_unlock_irq+0x27/0x80
> [ 448.286317] ? trace_hardirqs_on_caller+0x421/0x5c0
> [ 448.291337] ? do_int80_syscall_32+0x9f0/0x9f0
> [ 448.296277] ? _raw_spin_unlock_irq+0x60/0x80
> [ 448.300761] ? finish_task_switch+0x1f4/0x890
> [ 448.305411] ? syscall_return_slowpath+0x215/0x4e0
> [ 448.310337] ? prepare_exit_to_usermode+0x300/0x300
> [ 448.315348] ? sysret32_from_system_call+0x5/0x3c
> [ 448.320187] ? trace_hardirqs_off_thunk+0x1a/0x1c
> [ 448.325080] entry_SYSENTER_compat+0x70/0x7f
> [ 448.329492] RIP: 0023:0xf7f8fcb9
> [ 448.332846] RSP: 002b:00000000f7f8b0cc EFLAGS: 00000296 ORIG_RAX: 0000000000000003
> [ 448.340546] RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000020001000
> [ 448.347796] RDX: 00000000ffffff20 RSI: 0000000000000000 RDI: 0000000000000000
> [ 448.355047] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
> [ 448.362301] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> [ 448.369595] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> [ 448.376890]
> [ 448.378514] Allocated by task 9010:
> [ 448.382133] save_stack+0x43/0xd0
> [ 448.385681] kasan_kmalloc+0xc7/0xe0
> [ 448.389408] kasan_slab_alloc+0x12/0x20
> [ 448.393373] kmem_cache_alloc+0x12e/0x790
> [ 448.397518] __fuse_request_alloc+0x23/0xc0
> [ 448.401827] __fuse_get_req+0x186/0x8d0
> [ 448.405790] fuse_simple_request+0x20/0x610
> [ 448.410101] fuse_do_setattr+0x820/0x1f60
> [ 448.414262] fuse_setattr+0x1a6/0x470
> [ 448.418074] notify_change+0x779/0xda0
> [ 448.421942] utimes_common.isra.1+0x3f8/0x7f0
> [ 448.426420] do_utimes+0x199/0x250
> [ 448.430053] compat_SyS_utimes+0x1f8/0x2e0
> [ 448.434563] do_fast_syscall_32+0x3d5/0x1016
> [ 448.438956] entry_SYSENTER_compat+0x70/0x7f
> [ 448.443357]
> [ 448.444974] Freed by task 9010:
> [ 448.448305] save_stack+0x43/0xd0
> [ 448.451740] __kasan_slab_free+0x102/0x150
> [ 448.455957] kasan_slab_free+0xe/0x10
> [ 448.459750] kmem_cache_free+0x83/0x2d0
> [ 448.463719] fuse_request_free+0x77/0x90
> [ 448.467762] fuse_put_request+0x22a/0x2d0
> [ 448.471901] fuse_simple_request+0x38a/0x610
> [ 448.476394] fuse_do_setattr+0x820/0x1f60
> [ 448.480525] fuse_setattr+0x1a6/0x470
> [ 448.484304] notify_change+0x779/0xda0
> [ 448.488342] utimes_common.isra.1+0x3f8/0x7f0
> [ 448.492918] do_utimes+0x199/0x250
> [ 448.496443] compat_SyS_utimes+0x1f8/0x2e0
> [ 448.500769] do_fast_syscall_32+0x3d5/0x1016
> [ 448.505172] entry_SYSENTER_compat+0x70/0x7f
> [ 448.509660]
> [ 448.511273] The buggy address belongs to the object at ffff8801cec98400
> [ 448.511273] which belongs to the cache fuse_request of size 448
> [ 448.524116] The buggy address is located 48 bytes inside of
> [ 448.524116] 448-byte region [ffff8801cec98400, ffff8801cec985c0)
> [ 448.535897] The buggy address belongs to the page:
> [ 448.540853] page:ffffea00073b2600 count:1 mapcount:0 mapping:ffff8801cec98000 index:0x0
> [ 448.549166] flags: 0x2fffc0000000100(slab)
> [ 448.553534] raw: 02fffc0000000100 ffff8801cec98000 0000000000000000 0000000100000008
> [ 448.561407] raw: ffffea0007656660 ffffea00076359e0 ffff8801d4de8680 0000000000000000
> [ 448.569270] page dumped because: kasan: bad access detected
> [ 448.574960]
> [ 448.576564] Memory state around the buggy address:
> [ 448.581477] ffff8801cec98300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [ 448.588871] ffff8801cec98380: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
> [ 448.596217] >ffff8801cec98400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [ 448.603596] ^
> [ 448.608507] ffff8801cec98480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [ 448.615843] ffff8801cec98500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> [ 448.623284] ==================================================================

Eric