[syzbot] KASAN: use-after-free Read in nilfs_segctor_confirm

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syzbot

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Oct 1, 2022, 9:48:40 AM10/1/22
to konishi...@gmail.com, linux-...@vger.kernel.org, linux...@vger.kernel.org, syzkall...@googlegroups.com
Hello,

syzbot found the following issue on:

HEAD commit: aaa11ce2ffc8 Add linux-next specific files for 20220923
git tree: linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=17db205c880000
kernel config: https://syzkaller.appspot.com/x/.config?x=186d1ff305f10294
dashboard link: https://syzkaller.appspot.com/bug?extid=b8c672b0e22615c80fe0
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=178843ef080000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16ba96c0880000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/95c7bf83c07e/disk-aaa11ce2.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b161cd56a7a3/vmlinux-aaa11ce2.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b8c672...@syzkaller.appspotmail.com

loop0: detected capacity change from 0 to 2048
==================================================================
BUG: KASAN: use-after-free in nilfs_segctor_confirm+0x175/0x190 fs/nilfs2/segment.c:837
Read of size 8 at addr ffff88801274fc30 by task syz-executor290/3609

CPU: 0 PID: 3609 Comm: syz-executor290 Not tainted 6.0.0-rc6-next-20220923-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/22/2022
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:284 [inline]
print_report+0x15e/0x45d mm/kasan/report.c:395
kasan_report+0xbb/0x1f0 mm/kasan/report.c:495
nilfs_segctor_confirm+0x175/0x190 fs/nilfs2/segment.c:837
nilfs_segctor_destroy fs/nilfs2/segment.c:2727 [inline]
nilfs_detach_log_writer+0x856/0x9f0 fs/nilfs2/segment.c:2808
nilfs_put_super+0x3f/0x1a0 fs/nilfs2/super.c:468
generic_shutdown_super+0x154/0x410 fs/super.c:491
kill_block_super+0x97/0xf0 fs/super.c:1427
deactivate_locked_super+0x94/0x160 fs/super.c:331
deactivate_super+0xad/0xd0 fs/super.c:362
cleanup_mnt+0x2ae/0x3d0 fs/namespace.c:1186
task_work_run+0x16b/0x270 kernel/task_work.c:179
exit_task_work include/linux/task_work.h:38 [inline]
do_exit+0xb35/0x2a20 kernel/exit.c:820
do_group_exit+0xd0/0x2a0 kernel/exit.c:950
__do_sys_exit_group kernel/exit.c:961 [inline]
__se_sys_exit_group kernel/exit.c:959 [inline]
__x64_sys_exit_group+0x3a/0x50 kernel/exit.c:959
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f7f96472ba9
Code: Unable to access opcode bytes at 0x7f7f96472b7f.
RSP: 002b:00007fff812c4e88 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 00007f7f964ea330 RCX: 00007f7f96472ba9
RDX: 000000000000003c RSI: 00000000000000e7 RDI: 0000000000000001
RBP: 0000000000000001 R08: ffffffffffffffc0 R09: 00007f7f964e4e40
R10: 00007f7f964e4e40 R11: 0000000000000246 R12: 00007f7f964ea330
R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000001
</TASK>

Allocated by task 3609:
kasan_save_stack+0x1e/0x40 mm/kasan/common.c:45
kasan_set_track+0x21/0x30 mm/kasan/common.c:52
____kasan_kmalloc mm/kasan/common.c:371 [inline]
____kasan_kmalloc mm/kasan/common.c:330 [inline]
__kasan_kmalloc+0xa1/0xb0 mm/kasan/common.c:380
kmalloc include/linux/slab.h:559 [inline]
kzalloc include/linux/slab.h:695 [inline]
nilfs_find_or_create_root+0x84/0x4d0 fs/nilfs2/the_nilfs.c:747
nilfs_attach_checkpoint+0xc1/0x4b0 fs/nilfs2/super.c:519
nilfs_fill_super fs/nilfs2/super.c:1064 [inline]
nilfs_mount+0xb12/0xfb0 fs/nilfs2/super.c:1317
legacy_get_tree+0x105/0x220 fs/fs_context.c:610
vfs_get_tree+0x89/0x2f0 fs/super.c:1530
do_new_mount fs/namespace.c:3040 [inline]
path_mount+0x1326/0x1e20 fs/namespace.c:3370
do_mount fs/namespace.c:3383 [inline]
__do_sys_mount fs/namespace.c:3591 [inline]
__se_sys_mount fs/namespace.c:3568 [inline]
__x64_sys_mount+0x27f/0x300 fs/namespace.c:3568
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

Freed by task 3609:
kasan_save_stack+0x1e/0x40 mm/kasan/common.c:45
kasan_set_track+0x21/0x30 mm/kasan/common.c:52
kasan_save_free_info+0x2a/0x40 mm/kasan/generic.c:511
____kasan_slab_free mm/kasan/common.c:236 [inline]
____kasan_slab_free+0x160/0x1c0 mm/kasan/common.c:200
kasan_slab_free include/linux/kasan.h:177 [inline]
slab_free_hook mm/slub.c:1669 [inline]
slab_free_freelist_hook+0x8b/0x1c0 mm/slub.c:1695
slab_free mm/slub.c:3599 [inline]
__kmem_cache_free+0xab/0x3b0 mm/slub.c:3612
nilfs_put_root+0xb1/0xd0 fs/nilfs2/the_nilfs.c:804
nilfs_clear_inode+0x29a/0x330 fs/nilfs2/inode.c:895
nilfs_evict_inode+0x318/0x440 fs/nilfs2/inode.c:908
evict+0x2ed/0x6b0 fs/inode.c:664
dispose_list+0x117/0x1e0 fs/inode.c:697
evict_inodes+0x352/0x450 fs/inode.c:747
generic_shutdown_super+0xab/0x410 fs/super.c:479
kill_block_super+0x97/0xf0 fs/super.c:1427
deactivate_locked_super+0x94/0x160 fs/super.c:331
deactivate_super+0xad/0xd0 fs/super.c:362
cleanup_mnt+0x2ae/0x3d0 fs/namespace.c:1186
task_work_run+0x16b/0x270 kernel/task_work.c:179
exit_task_work include/linux/task_work.h:38 [inline]
do_exit+0xb35/0x2a20 kernel/exit.c:820
do_group_exit+0xd0/0x2a0 kernel/exit.c:950
__do_sys_exit_group kernel/exit.c:961 [inline]
__se_sys_exit_group kernel/exit.c:959 [inline]
__x64_sys_exit_group+0x3a/0x50 kernel/exit.c:959
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

The buggy address belongs to the object at ffff88801274fc00
which belongs to the cache kmalloc-256 of size 256
The buggy address is located 48 bytes inside of
256-byte region [ffff88801274fc00, ffff88801274fd00)

The buggy address belongs to the physical page:
page:ffffea000049d380 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1274e
head:ffffea000049d380 order:1 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 ffff888011841b40 dead000080100010 0000000000000000
raw: 0000000000000000 dead000000000001 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 1, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, tgid 1 (swapper/0), ts 2053424585, free_ts 0
prep_new_page mm/page_alloc.c:2538 [inline]
get_page_from_freelist+0x1092/0x2d20 mm/page_alloc.c:4287
__alloc_pages+0x1c7/0x5a0 mm/page_alloc.c:5546
alloc_page_interleave+0x1e/0x200 mm/mempolicy.c:2113
alloc_pages+0x22f/0x270 mm/mempolicy.c:2275
alloc_slab_page mm/slub.c:1739 [inline]
allocate_slab+0x213/0x300 mm/slub.c:1884
new_slab mm/slub.c:1937 [inline]
___slab_alloc+0xac1/0x1430 mm/slub.c:3119
__slab_alloc.constprop.0+0x4d/0xa0 mm/slub.c:3217
slab_alloc_node mm/slub.c:3302 [inline]
__kmem_cache_alloc_node+0x18a/0x3d0 mm/slub.c:3375
__do_kmalloc_node mm/slab_common.c:933 [inline]
__kmalloc_node_track_caller+0x45/0xc0 mm/slab_common.c:954
__do_krealloc mm/slab_common.c:1318 [inline]
krealloc+0x8c/0xf0 mm/slab_common.c:1351
add_sysfs_param+0xca/0x960 kernel/params.c:651
kernel_add_sysfs_param kernel/params.c:812 [inline]
param_sysfs_builtin kernel/params.c:851 [inline]
param_sysfs_init+0x301/0x43b kernel/params.c:970
do_one_initcall+0x13d/0x780 init/main.c:1307
do_initcall_level init/main.c:1382 [inline]
do_initcalls init/main.c:1398 [inline]
do_basic_setup init/main.c:1417 [inline]
kernel_init_freeable+0x6ff/0x788 init/main.c:1637
kernel_init+0x1a/0x1d0 init/main.c:1525
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306
page_owner free stack trace missing

Memory state around the buggy address:
ffff88801274fb00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88801274fb80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88801274fc00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88801274fc80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88801274fd00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

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syzbot can test patches for this issue, for details see:
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Khalid Masum

unread,
Oct 2, 2022, 5:25:27 AM10/2/22
to konishi...@gmail.com, linux-...@vger.kernel.org, linux...@vger.kernel.org, syzkall...@googlegroups.com, syzbot
Hi all,

The reproducer triggers the same bug in upstream 6.0-rc7 as well.


Thanks,

  -- Khalid Masum

Ryusuke Konishi

unread,
Oct 2, 2022, 11:52:36 AM10/2/22
to 00000000000021...@google.com, linux-...@vger.kernel.org, linux...@vger.kernel.org, syzkall...@googlegroups.com, syzbot
It looks like this and a few similar issues are caused by duplicate
inode allocation with the same inode number
as the root inode on a corrupted disk image.

I'm now digging into the issue and trying to fix it.

Thanks,
Ryusuke Konishi

Ryusuke Konishi

unread,
Oct 3, 2022, 11:05:26 AM10/3/22
to Andrew Morton, linux-nilfs, syzbot, syzkall...@googlegroups.com, LKML
If the beginning of the inode bitmap area is corrupted on disk, an
inode with the same inode number as the root inode can be allocated
and fail soon after. In this case, the subsequent call to
nilfs_clear_inode() on that bogus root inode will wrongly decrement
the reference counter of struct nilfs_root, and this will erroneously
free struct nilfs_root, causing kernel oopses.

This fixes the problem by changing nilfs_new_inode() to skip reserved
inode numbers while repairing the inode bitmap.

Signed-off-by: Ryusuke Konishi <konishi...@gmail.com>
Reported-by: syzbot+b8c672...@syzkaller.appspotmail.com
Reported-by: Khalid Masum <khalid....@gmail.com>
Tested-by: Ryusuke Konishi <konishi...@gmail.com>
Cc: sta...@vger.kernel.org
---
fs/nilfs2/inode.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/fs/nilfs2/inode.c b/fs/nilfs2/inode.c
index 67f63cfeade5..b074144f6f83 100644
--- a/fs/nilfs2/inode.c
+++ b/fs/nilfs2/inode.c
@@ -328,6 +328,7 @@ struct inode *nilfs_new_inode(struct inode *dir, umode_t mode)
struct inode *inode;
struct nilfs_inode_info *ii;
struct nilfs_root *root;
+ struct buffer_head *bh;
int err = -ENOMEM;
ino_t ino;

@@ -343,11 +344,25 @@ struct inode *nilfs_new_inode(struct inode *dir, umode_t mode)
ii->i_state = BIT(NILFS_I_NEW);
ii->i_root = root;

- err = nilfs_ifile_create_inode(root->ifile, &ino, &ii->i_bh);
+ err = nilfs_ifile_create_inode(root->ifile, &ino, &bh);
if (unlikely(err))
goto failed_ifile_create_inode;
/* reference count of i_bh inherits from nilfs_mdt_read_block() */

+ if (unlikely(ino < NILFS_USER_INO)) {
+ nilfs_warn(sb,
+ "inode bitmap is inconsistent for reserved inodes");
+ do {
+ brelse(bh);
+ err = nilfs_ifile_create_inode(root->ifile, &ino, &bh);
+ if (unlikely(err))
+ goto failed_ifile_create_inode;
+ } while (ino < NILFS_USER_INO);
+
+ nilfs_info(sb, "repaired inode bitmap for reserved inodes");
+ }
+ ii->i_bh = bh;
+
atomic64_inc(&root->inodes_count);
inode_init_owner(&init_user_ns, inode, dir, mode);
inode->i_ino = ino;
--
2.34.1

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