Re: [syzbot] [btrfs?] KASAN: slab-use-after-free Read in btrfs_open_devices

From: syzbot
Date: Thu Aug 10 2023 - 09:05:39 EST


Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: use-after-free Read in btrfs_test_super

==================================================================
BUG: KASAN: use-after-free in btrfs_test_super+0x9b/0xa0 fs/btrfs/super.c:1346
Read of size 8 at addr ffff88802a975110 by task syz-executor.3/5661

CPU: 1 PID: 5661 Comm: syz-executor.3 Not tainted 6.5.0-rc5-next-20230807-syzkaller-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/26/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:364 [inline]
print_report+0xc4/0x620 mm/kasan/report.c:475
kasan_report+0xda/0x110 mm/kasan/report.c:588
btrfs_test_super+0x9b/0xa0 fs/btrfs/super.c:1346
sget+0x3de/0x610 fs/super.c:663
btrfs_mount_root+0x220/0xd50 fs/btrfs/super.c:1475
legacy_get_tree+0x109/0x220 fs/fs_context.c:611
vfs_get_tree+0x88/0x350 fs/super.c:1544
fc_mount fs/namespace.c:1112 [inline]
vfs_kern_mount.part.0+0xcb/0x170 fs/namespace.c:1142
vfs_kern_mount+0x3f/0x60 fs/namespace.c:1129
btrfs_mount+0x292/0xb10 fs/btrfs/super.c:1578
legacy_get_tree+0x109/0x220 fs/fs_context.c:611
vfs_get_tree+0x88/0x350 fs/super.c:1544
do_new_mount fs/namespace.c:3335 [inline]
path_mount+0x1492/0x1ed0 fs/namespace.c:3662
do_mount fs/namespace.c:3675 [inline]
__do_sys_mount fs/namespace.c:3884 [inline]
__se_sys_mount fs/namespace.c:3861 [inline]
__x64_sys_mount+0x293/0x310 fs/namespace.c:3861
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f0d83a7e1ea
Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb a6 e8 de 09 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f0d847a2ee8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f0d847a2f80 RCX: 00007f0d83a7e1ea
RDX: 00000000200051c0 RSI: 0000000020005200 RDI: 00007f0d847a2f40
RBP: 00000000200051c0 R08: 00007f0d847a2f80 R09: 0000000001000008
R10: 0000000001000008 R11: 0000000000000246 R12: 0000000020005200
R13: 00007f0d847a2f40 R14: 00000000000051ab R15: 0000000020000280
</TASK>

The buggy address belongs to the physical page:
page:ffffea0000aa5d40 refcount:0 mapcount:0 mapping:0000000000000000 index:0x4 pfn:0x2a975
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000000 0000000000000000 ffffffff00000201 0000000000000000
raw: 0000000000000004 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 2, migratetype Unmovable, gfp_mask 0x152dc0(GFP_USER|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_ZERO), pid 5641, tgid 5640 (syz-executor.0), ts 80709504641, free_ts 80731761534
set_page_owner include/linux/page_owner.h:31 [inline]
post_alloc_hook+0x2d2/0x350 mm/page_alloc.c:1567
prep_new_page mm/page_alloc.c:1574 [inline]
get_page_from_freelist+0x10d7/0x31b0 mm/page_alloc.c:3253
__alloc_pages+0x1d0/0x4a0 mm/page_alloc.c:4509
__alloc_pages_node include/linux/gfp.h:237 [inline]
alloc_pages_node include/linux/gfp.h:260 [inline]
__kmalloc_large_node+0x87/0x1c0 mm/slab_common.c:1164
__do_kmalloc_node mm/slab_common.c:1011 [inline]
__kmalloc_node.cold+0x5/0xdd mm/slab_common.c:1030
kmalloc_node include/linux/slab.h:619 [inline]
kvmalloc_node+0x6f/0x1a0 mm/util.c:604
kvmalloc include/linux/slab.h:737 [inline]
kvzalloc include/linux/slab.h:745 [inline]
btrfs_mount_root+0xe8/0xd50 fs/btrfs/super.c:1461
legacy_get_tree+0x109/0x220 fs/fs_context.c:611
vfs_get_tree+0x88/0x350 fs/super.c:1544
fc_mount fs/namespace.c:1112 [inline]
vfs_kern_mount.part.0+0xcb/0x170 fs/namespace.c:1142
vfs_kern_mount+0x3f/0x60 fs/namespace.c:1129
btrfs_mount+0x292/0xb10 fs/btrfs/super.c:1578
legacy_get_tree+0x109/0x220 fs/fs_context.c:611
vfs_get_tree+0x88/0x350 fs/super.c:1544
do_new_mount fs/namespace.c:3335 [inline]
path_mount+0x1492/0x1ed0 fs/namespace.c:3662
do_mount fs/namespace.c:3675 [inline]
__do_sys_mount fs/namespace.c:3884 [inline]
__se_sys_mount fs/namespace.c:3861 [inline]
__x64_sys_mount+0x293/0x310 fs/namespace.c:3861
page last free stack trace:
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1158 [inline]
free_unref_page_prepare+0x508/0xb90 mm/page_alloc.c:2380
free_unref_page+0x33/0x3b0 mm/page_alloc.c:2475
kvfree+0x47/0x50 mm/util.c:650
btrfs_mount_root+0x591/0xd50 fs/btrfs/super.c:1535
legacy_get_tree+0x109/0x220 fs/fs_context.c:611
vfs_get_tree+0x88/0x350 fs/super.c:1544
fc_mount fs/namespace.c:1112 [inline]
vfs_kern_mount.part.0+0xcb/0x170 fs/namespace.c:1142
vfs_kern_mount+0x3f/0x60 fs/namespace.c:1129
btrfs_mount+0x292/0xb10 fs/btrfs/super.c:1578
legacy_get_tree+0x109/0x220 fs/fs_context.c:611
vfs_get_tree+0x88/0x350 fs/super.c:1544
do_new_mount fs/namespace.c:3335 [inline]
path_mount+0x1492/0x1ed0 fs/namespace.c:3662
do_mount fs/namespace.c:3675 [inline]
__do_sys_mount fs/namespace.c:3884 [inline]
__se_sys_mount fs/namespace.c:3861 [inline]
__x64_sys_mount+0x293/0x310 fs/namespace.c:3861
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

Memory state around the buggy address:
ffff88802a975000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff88802a975080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88802a975100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff88802a975180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff88802a975200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


Tested on:

commit: f7dc24b3 Add linux-next specific files for 20230807
git tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
console output: https://syzkaller.appspot.com/x/log.txt?x=14a2c5aba80000
kernel config: https://syzkaller.appspot.com/x/.config?x=d7847c9dca13d6c5
dashboard link: https://syzkaller.appspot.com/bug?extid=26860029a4d562566231
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch: https://syzkaller.appspot.com/x/patch.diff?x=128199aba80000