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Subject: Re: KASAN: use-after-free Read in fuse_dev_do_read
To:     syzbot <syzbot+4e975615ca01f2277bdd@syzkaller.appspotmail.com>,
        dvyukov@google.com, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, miklos@szeredi.hu,
        syzkaller-bugs@googlegroups.com
References: <00000000000059484105767ac88f@google.com>
From:   Kirill Tkhai <ktkhai@virtuozzo.com>
Message-ID: <be262e04-df8a-c248-26a8-d42bf081be1c@virtuozzo.com>
Date:   Mon, 24 Sep 2018 15:06:34 +0300
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On 22.09.2018 22:30, syzbot wrote:
> syzbot has found a reproducer for the following crash on:
> 
> HEAD commit:    10dc890d4228 Merge tag 'pinctrl-v4.19-3' of git://git.kern..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1631cfbe400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=5fa12be50bca08d8
> dashboard link: https://syzkaller.appspot.com/bug?extid=4e975615ca01f2277bdd
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15ffb766400000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+4e975615ca01f2277bdd@syzkaller.appspotmail.com
> 
> 8021q: adding VLAN 0 to HW filter on device team0
> 8021q: adding VLAN 0 to HW filter on device team0
> 8021q: adding VLAN 0 to HW filter on device team0
> 8021q: adding VLAN 0 to HW filter on device team0
> ==================================================================
> BUG: KASAN: use-after-free in constant_test_bit arch/x86/include/asm/bitops.h:328 [inline]
> BUG: KASAN: use-after-free in fuse_dev_do_read.isra.27+0x1659/0x1920 fs/fuse/dev.c:1318
> Read of size 8 at addr ffff8801d8702630 by task syz-executor1/7794
> 
> CPU: 0 PID: 7794 Comm: syz-executor1 Not tainted 4.19.0-rc4+ #26
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x1c4/0x2b4 lib/dump_stack.c:113
>  print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256
>  kasan_report_error mm/kasan/report.c:354 [inline]
>  kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412
>  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
>  constant_test_bit arch/x86/include/asm/bitops.h:328 [inline]
>  fuse_dev_do_read.isra.27+0x1659/0x1920 fs/fuse/dev.c:1318
>  fuse_dev_read+0x1a9/0x250 fs/fuse/dev.c:1360
>  call_read_iter include/linux/fs.h:1802 [inline]
>  new_sync_read fs/read_write.c:406 [inline]
>  __vfs_read+0x6ac/0x9b0 fs/read_write.c:418
>  vfs_read+0x17f/0x3c0 fs/read_write.c:452
>  ksys_read+0x101/0x260 fs/read_write.c:578
>  __do_sys_read fs/read_write.c:588 [inline]
>  __se_sys_read fs/read_write.c:586 [inline]
>  __x64_sys_read+0x73/0xb0 fs/read_write.c:586
>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x457679
> Code: 1d b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 eb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007f6a5aeedc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
> RAX: ffffffffffffffda RBX: 00007f6a5aeee6d4 RCX: 0000000000457679
> RDX: 0000000000001000 RSI: 0000000020001000 RDI: 0000000000000003
> RBP: 000000000072bf00 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
> R13: 00000000004d4ad0 R14: 00000000004c31e5 R15: 0000000000000000
> 
> Allocated by task 7801:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>  set_track mm/kasan/kasan.c:460 [inline]
>  kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
>  kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490
>  kmem_cache_alloc+0x12e/0x730 mm/slab.c:3554
>  __fuse_request_alloc+0x27/0xf0 fs/fuse/dev.c:58
>  fuse_request_alloc+0x18/0x20 fs/fuse/dev.c:89
>  fuse_fill_super+0x12bf/0x1ea0 fs/fuse/inode.c:1157
>  mount_nodev+0x6b/0x110 fs/super.c:1204
>  fuse_mount+0x2c/0x40 fs/fuse/inode.c:1213
>  mount_fs+0xae/0x31d fs/super.c:1261
>  vfs_kern_mount.part.35+0xdc/0x4f0 fs/namespace.c:961
>  vfs_kern_mount fs/namespace.c:951 [inline]
>  do_new_mount fs/namespace.c:2457 [inline]
>  do_mount+0x581/0x31f0 fs/namespace.c:2787
>  ksys_mount+0x12d/0x140 fs/namespace.c:3003
>  __do_sys_mount fs/namespace.c:3017 [inline]
>  __se_sys_mount fs/namespace.c:3014 [inline]
>  __x64_sys_mount+0xbe/0x150 fs/namespace.c:3014
>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> Freed by task 7801:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>  set_track mm/kasan/kasan.c:460 [inline]
>  __kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521
>  kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
>  __cache_free mm/slab.c:3498 [inline]
>  kmem_cache_free+0x83/0x290 mm/slab.c:3756
>  fuse_request_free+0x8b/0xa0 fs/fuse/dev.c:104
>  fuse_put_request+0x2a6/0x350 fs/fuse/dev.c:304
>  request_end+0xba/0xaa0 fs/fuse/dev.c:414
>  fuse_dev_do_write+0x192e/0x36e0 fs/fuse/dev.c:1915
>  fuse_dev_write+0x19a/0x240 fs/fuse/dev.c:1939
>  call_write_iter include/linux/fs.h:1808 [inline]
>  new_sync_write fs/read_write.c:474 [inline]
>  __vfs_write+0x6b8/0x9f0 fs/read_write.c:487
>  vfs_write+0x1fc/0x560 fs/read_write.c:549
>  ksys_write+0x101/0x260 fs/read_write.c:598
>  __do_sys_write fs/read_write.c:610 [inline]
>  __se_sys_write fs/read_write.c:607 [inline]
>  __x64_sys_write+0x73/0xb0 fs/read_write.c:607
>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> The buggy address belongs to the object at ffff8801d8702600
>  which belongs to the cache fuse_request of size 448
> The buggy address is located 48 bytes inside of
>  448-byte region [ffff8801d8702600, ffff8801d87027c0)
> The buggy address belongs to the page:
> page:ffffea000761c080 count:1 mapcount:0 mapping:ffff8801d4a0e240 index:0x0
> flags: 0x2fffc0000000100(slab)
> raw: 02fffc0000000100 ffffea0006ec0e88 ffffea0006ee91c8 ffff8801d4a0e240
> raw: 0000000000000000 ffff8801d8702000 0000000100000008 0000000000000000
> page dumped because: kasan: bad access detected
> 
> Memory state around the buggy address:
>  ffff8801d8702500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8801d8702580: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>> ffff8801d8702600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                      ^
>  ffff8801d8702680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff8801d8702700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================

Fix from my previous message makes the use-after-free does not reproduce
with the reproducer in my setup.

I can prepare the patch, but before this some comments from Miklos would
be welcome.

Miklos, what you think about this?

Kirill
---
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 11ea2c4a38ab..675caed3e655 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1311,12 +1311,14 @@ static ssize_t fuse_dev_do_read(struct fuse_dev *fud, struct file *file,
 		goto out_end;
 	}
 	list_move_tail(&req->list, &fpq->processing);
+	__fuse_get_request(req);
 	spin_unlock(&fpq->lock);
 	set_bit(FR_SENT, &req->flags);
 	/* matches barrier in request_wait_answer() */
 	smp_mb__after_atomic();
 	if (test_bit(FR_INTERRUPTED, &req->flags))
 		queue_interrupt(fiq, req);
+	fuse_put_request(fc, req);
 
 	return reqsize;