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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: b229b6ca5abb Merge tag 'perf-tools-fixes-for-v6.1-2022-10-..
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=169ba3e2880000
kernel config: https://syzkaller.appspot.com/x/.config?x=1d3548a4365ba17d
dashboard link: https://syzkaller.appspot.com/bug?extid=f816fa82f8783f7a02bb
compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14687046880000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10dff35e880000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/24728b72a896/disk-b229b6ca.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/10a3c40c60e1/vmlinux-b229b6ca.xz
kernel image: https://storage.googleapis.com/syzbot-assets/69f963b02b7e/bzImage-b229b6ca.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/03acc269b955/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f816fa...@syzkaller.appspotmail.com

BUG: KASAN: use-after-free in debug_spin_lock_before kernel/locking/spinlock_debug.c:85 [inline]
BUG: KASAN: use-after-free in do_raw_spin_lock+0x28b/0x360 kernel/locking/spinlock_debug.c:114
Read of size 4 at addr ffff8880753301a4 by task syz-executor407/3709

CPU: 1 PID: 3709 Comm: syz-executor407 Not tainted 6.1.0-rc2-syzkaller-00105-gb229b6ca5abb #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/11/2022
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x1b1/0x28e lib/dump_stack.c:106
print_address_description+0x74/0x340 mm/kasan/report.c:284
print_report+0x107/0x1f0 mm/kasan/report.c:395
kasan_report+0xcd/0x100 mm/kasan/report.c:495
debug_spin_lock_before kernel/locking/spinlock_debug.c:85 [inline]
do_raw_spin_lock+0x28b/0x360 kernel/locking/spinlock_debug.c:114
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:111 [inline]
_raw_spin_lock_irqsave+0xbf/0x100 kernel/locking/spinlock.c:162
finish_wait+0xba/0x1d0 kernel/sched/wait.c:406
nilfs_segctor_sync+0x457/0x5c0 fs/nilfs2/segment.c:2197
nilfs_construct_segment fs/nilfs2/segment.c:2251 [inline]
nilfs_transaction_commit+0x593/0x760 fs/nilfs2/segment.c:285
nilfs_evict_inode+0x322/0x3d0 fs/nilfs2/inode.c:945
evict+0x2a4/0x620 fs/inode.c:664
d_delete_notify include/linux/fsnotify.h:261 [inline]
vfs_rmdir+0x37e/0x4b0 fs/namei.c:4133
do_rmdir+0x39d/0x610 fs/namei.c:4181
__do_sys_rmdir fs/namei.c:4200 [inline]
__se_sys_rmdir fs/namei.c:4198 [inline]
__x64_sys_rmdir+0x45/0x50 fs/namei.c:4198
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f8b354df179
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f8b354692f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000054
RAX: ffffffffffffffda RBX: 00007f8b355664b0 RCX: 00007f8b354df179
RDX: 00007f8b35469700 RSI: ed621b9e8ef83f76 RDI: 0000000020000040
RBP: 00007f8b35531720 R08: 00007f8b35469700 R09: 0000000000000000
R10: 00007f8b35469700 R11: 0000000000000246 R12: 00007f8b355312f8
R13: 00007f8b355310b8 R14: 0030656c69662f2e R15: 00007f8b355664b8
</TASK>

Allocated by task 3700:
kasan_save_stack mm/kasan/common.c:45 [inline]
kasan_set_track+0x3d/0x60 mm/kasan/common.c:52
____kasan_kmalloc mm/kasan/common.c:371 [inline]
__kasan_kmalloc+0x97/0xb0 mm/kasan/common.c:380
kmalloc include/linux/slab.h:576 [inline]
kzalloc include/linux/slab.h:712 [inline]
nilfs_segctor_new fs/nilfs2/segment.c:2657 [inline]
nilfs_attach_log_writer+0x133/0x8d0 fs/nilfs2/segment.c:2786
nilfs_fill_super+0x38b/0x5d0 fs/nilfs2/super.c:1073
nilfs_mount+0x613/0x9b0 fs/nilfs2/super.c:1317
legacy_get_tree+0xea/0x180 fs/fs_context.c:610
vfs_get_tree+0x88/0x270 fs/super.c:1530
do_new_mount+0x289/0xad0 fs/namespace.c:3040
do_mount fs/namespace.c:3383 [inline]
__do_sys_mount fs/namespace.c:3591 [inline]
__se_sys_mount+0x2d3/0x3c0 fs/namespace.c:3568
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

Freed by task 3700:
kasan_save_stack mm/kasan/common.c:45 [inline]
kasan_set_track+0x3d/0x60 mm/kasan/common.c:52
kasan_save_free_info+0x27/0x40 mm/kasan/generic.c:511
____kasan_slab_free+0xd6/0x120 mm/kasan/common.c:236
kasan_slab_free include/linux/kasan.h:177 [inline]
slab_free_hook mm/slub.c:1724 [inline]
slab_free_freelist_hook+0x12e/0x1a0 mm/slub.c:1750
slab_free mm/slub.c:3661 [inline]
__kmem_cache_free+0x71/0x110 mm/slub.c:3674
nilfs_segctor_destroy fs/nilfs2/segment.c:2756 [inline]
nilfs_detach_log_writer+0x8f3/0xbd0 fs/nilfs2/segment.c:2813
nilfs_attach_log_writer+0xe8/0x8d0 fs/nilfs2/segment.c:2783
nilfs_remount+0x382/0x410 fs/nilfs2/super.c:1171
reconfigure_super+0x3bc/0x7b0 fs/super.c:934
do_remount fs/namespace.c:2702 [inline]
path_mount+0xd20/0x10c0 fs/namespace.c:3362
do_mount fs/namespace.c:3383 [inline]
__do_sys_mount fs/namespace.c:3591 [inline]
__se_sys_mount+0x2d3/0x3c0 fs/namespace.c:3568
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd

The buggy address belongs to the object at ffff888075330000
which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 420 bytes inside of
1024-byte region [ffff888075330000, ffff888075330400)

The buggy address belongs to the physical page:
page:ffffea0001d4cc00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x75330
head:ffffea0001d4cc00 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 ffffea0001f4c000 dead000000000002 ffff888012041dc0
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd2a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 3392, tgid 3392 (sshd), ts 33251724611, free_ts 32678605279
prep_new_page mm/page_alloc.c:2538 [inline]
get_page_from_freelist+0x742/0x7c0 mm/page_alloc.c:4287
__alloc_pages+0x259/0x560 mm/page_alloc.c:5554
alloc_slab_page+0x70/0xf0 mm/slub.c:1794
allocate_slab+0x5e/0x4b0 mm/slub.c:1939
new_slab mm/slub.c:1992 [inline]
___slab_alloc+0x782/0xe20 mm/slub.c:3180
__slab_alloc mm/slub.c:3279 [inline]
slab_alloc_node mm/slub.c:3364 [inline]
__kmem_cache_alloc_node+0x252/0x310 mm/slub.c:3437
__do_kmalloc_node mm/slab_common.c:954 [inline]
__kmalloc_node_track_caller+0x9c/0x1a0 mm/slab_common.c:975
kmalloc_reserve net/core/skbuff.c:437 [inline]
__alloc_skb+0x112/0x2b0 net/core/skbuff.c:509
alloc_skb include/linux/skbuff.h:1267 [inline]
__tcp_send_ack+0x98/0x5f0 net/ipv4/tcp_output.c:3960
tcp_cleanup_rbuf net/ipv4/tcp.c:1628 [inline]
tcp_recvmsg_locked+0x1cf3/0x25c0 net/ipv4/tcp.c:2649
tcp_recvmsg+0x337/0x870 net/ipv4/tcp.c:2679
inet_recvmsg+0x13a/0x250 net/ipv4/af_inet.c:859
sock_recvmsg_nosec net/socket.c:995 [inline]
sock_recvmsg net/socket.c:1013 [inline]
sock_read_iter+0x3fa/0x530 net/socket.c:1086
call_read_iter include/linux/fs.h:2185 [inline]
new_sync_read fs/read_write.c:389 [inline]
vfs_read+0x7ac/0xbf0 fs/read_write.c:470
ksys_read+0x177/0x2a0 fs/read_write.c:613
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
page last free stack trace:
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1458 [inline]
free_pcp_prepare+0x80c/0x8f0 mm/page_alloc.c:1508
free_unref_page_prepare mm/page_alloc.c:3386 [inline]
free_unref_page+0x7d/0x5f0 mm/page_alloc.c:3482
qlist_free_all+0x2b/0x70 mm/kasan/quarantine.c:187
kasan_quarantine_reduce+0x169/0x180 mm/kasan/quarantine.c:294
__kasan_slab_alloc+0x1f/0x70 mm/kasan/common.c:302
kasan_slab_alloc include/linux/kasan.h:201 [inline]
slab_post_alloc_hook mm/slab.h:737 [inline]
slab_alloc_node mm/slub.c:3398 [inline]
slab_alloc mm/slub.c:3406 [inline]
__kmem_cache_alloc_lru mm/slub.c:3413 [inline]
kmem_cache_alloc+0x1cc/0x300 mm/slub.c:3422
kmem_cache_zalloc include/linux/slab.h:702 [inline]
alloc_buffer_head+0x20/0xf0 fs/buffer.c:2899
alloc_page_buffers+0x179/0x460 fs/buffer.c:829
create_empty_buffers+0x36/0xe30 fs/buffer.c:1543
ext4_block_write_begin+0x2e5/0x2290 fs/ext4/inode.c:1074
ext4_da_write_begin+0x539/0x760 fs/ext4/inode.c:3003
generic_perform_write+0x2e4/0x5e0 mm/filemap.c:3753
ext4_buffered_write_iter+0x122/0x3a0 fs/ext4/file.c:285
ext4_file_write_iter+0x1d0/0x18d0
call_write_iter include/linux/fs.h:2191 [inline]
new_sync_write fs/read_write.c:491 [inline]
vfs_write+0x7dc/0xc50 fs/read_write.c:584
ksys_write+0x177/0x2a0 fs/read_write.c:637

Memory state around the buggy address:
ffff888075330080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888075330100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888075330180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888075330200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888075330280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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[Ryusuke Konishi]

If a nilfs2 filesystem is downgraded to read-only due to metadata
corruption on disk and is remounted read/write, or if emergency
read-only remount is performed, detaching a log writer and
synchronizing the filesystem can be done at the same time.

In these cases, use-after-free of the log writer (hereinafter
nilfs->ns_writer) can happen as shown in the scenario below:

Task1 Task2
-------------------------------- ------------------------------
nilfs_construct_segment
nilfs_segctor_sync
init_wait
init_waitqueue_entry
add_wait_queue
schedule
nilfs_remount (R/W remount case)
nilfs_attach_log_writer
nilfs_detach_log_writer
nilfs_segctor_destroy
kfree
finish_wait
_raw_spin_lock_irqsave
__raw_spin_lock_irqsave
do_raw_spin_lock
debug_spin_lock_before <-- use-after-free

While Task1 is sleeping, nilfs->ns_writer is freed by Task2. After
Task1 waked up, Task1 accesses nilfs->ns_writer which is already
freed. This scenario diagram is based on the Shigeru Yoshida's post
[1].

This patch fixes the issue by not detaching nilfs->ns_writer on
remount so that this UAF race doesn't happen. Along with this change,
this patch also inserts a few necessary read-only checks with
superblock instance where only the ns_writer pointer was used to check
if the filesystem is read-only.

Link: https://syzkaller.appspot.com/bug?id=79a4c002e960419ca173d55e863bd09e8112df8b
Link: https://lkml.kernel.org/r/20221103141759.1...@redhat.com [1]
Signed-off-by: Ryusuke Konishi <konishi...@gmail.com>
Reported-by: syzbot+f816fa...@syzkaller.appspotmail.com
Reported-by: Shigeru Yoshida <syos...@redhat.com>
Tested-by: Ryusuke Konishi <konishi...@gmail.com>
Cc: sta...@vger.kernel.org
---
fs/nilfs2/segment.c | 15 ++++++++-------
fs/nilfs2/super.c | 2 --
2 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index b4cebad21b48..3335ef352915 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -317,7 +317,7 @@ void nilfs_relax_pressure_in_lock(struct super_block *sb)
struct the_nilfs *nilfs = sb->s_fs_info;
struct nilfs_sc_info *sci = nilfs->ns_writer;

- if (!sci || !sci->sc_flush_request)
+ if (sb_rdonly(sb) || unlikely(!sci) || !sci->sc_flush_request)
return;

set_bit(NILFS_SC_PRIOR_FLUSH, &sci->sc_flags);
@@ -2242,7 +2242,7 @@ int nilfs_construct_segment(struct super_block *sb)
struct nilfs_sc_info *sci = nilfs->ns_writer;
struct nilfs_transaction_info *ti;

- if (!sci)
+ if (sb_rdonly(sb) || unlikely(!sci))
return -EROFS;

/* A call inside transactions causes a deadlock. */
@@ -2280,7 +2280,7 @@ int nilfs_construct_dsync_segment(struct super_block *sb, struct inode *inode,
struct nilfs_transaction_info ti;
int err = 0;

- if (!sci)
+ if (sb_rdonly(sb) || unlikely(!sci))
return -EROFS;

nilfs_transaction_lock(sb, &ti, 0);
@@ -2776,11 +2776,12 @@ int nilfs_attach_log_writer(struct super_block *sb, struct nilfs_root *root)

if (nilfs->ns_writer) {
/*
- * This happens if the filesystem was remounted
- * read/write after nilfs_error degenerated it into a
- * read-only mount.
+ * This happens if the filesystem is made read-only by
+ * __nilfs_error or nilfs_remount and then remounted
+ * read/write. In these cases, reuse the existing
+ * writer.
*/
- nilfs_detach_log_writer(sb);
+ return 0;
}

nilfs->ns_writer = nilfs_segctor_new(sb, root);
diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index ba108f915391..6edb6e0dd61f 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -1133,8 +1133,6 @@ static int nilfs_remount(struct super_block *sb, int *flags, char *data)
if ((bool)(*flags & SB_RDONLY) == sb_rdonly(sb))
goto out;
if (*flags & SB_RDONLY) {
- /* Shutting down log writer */
- nilfs_detach_log_writer(sb);
sb->s_flags |= SB_RDONLY;

/*
--
2.34.1