[syzbot] [nilfs2?] general protection fault in nilfs_btree_insert

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 51094a24b85e Merge tag 'hardening-v6.2-rc1-fixes' of git:/..
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=172e2b44480000
kernel config: https://syzkaller.appspot.com/x/.config?x=4e2d7bfa2d6d5a76
dashboard link: https://syzkaller.appspot.com/bug?extid=ede796cecd5296353515
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=1243578c480000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1506f1ac480000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/a26f3769fdfb/disk-51094a24.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5decc3ae71d7/vmlinux-51094a24.xz
kernel image: https://storage.googleapis.com/syzbot-assets/dd2ac18a5b04/bzImage-51094a24.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/559169c47ec8/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ede796...@syzkaller.appspotmail.com

loop0: detected capacity change from 0 to 2048
general protection fault, probably for non-canonical address 0xdffffc0000000005: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
CPU: 1 PID: 5066 Comm: syz-executor153 Not tainted 6.1.0-syzkaller-14587-g51094a24b85e #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
RIP: 0010:nilfs_btree_get_nonroot_node fs/nilfs2/btree.c:418 [inline]
RIP: 0010:nilfs_btree_prepare_insert fs/nilfs2/btree.c:1077 [inline]
RIP: 0010:nilfs_btree_insert+0x6d3/0x1c10 fs/nilfs2/btree.c:1238
Code: bc 24 80 00 00 00 4c 89 f8 48 c1 e8 03 42 80 3c 28 00 74 08 4c 89 ff e8 4b 02 92 fe 4d 8b 3f 49 83 c7 28 4c 89 f8 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 ff e8 2e 02 92 fe 4d 8b 3f 49 83 c7 02
RSP: 0018:ffffc90003bcf4a0 EFLAGS: 00010206
RAX: 0000000000000005 RBX: 0000000000000001 RCX: 0000000000000000
RDX: ffff88807eba3a80 RSI: 0000000000000002 RDI: 0000000000000001
RBP: ffffc90003bcf630 R08: ffffffff834f80d8 R09: ffffed100571ff9b
R10: ffffed100571ff9b R11: 1ffff1100571ff9a R12: ffff888021d03480
R13: dffffc0000000000 R14: 0000000000000002 R15: 0000000000000028
FS: 000055555588c300(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f4614ff5a70 CR3: 000000007eb7c000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
nilfs_bmap_do_insert fs/nilfs2/bmap.c:121 [inline]
nilfs_bmap_insert+0x20d/0x360 fs/nilfs2/bmap.c:147
nilfs_get_block+0x414/0x8d0 fs/nilfs2/inode.c:101
__block_write_begin_int+0x54c/0x1a80 fs/buffer.c:1991
__block_write_begin fs/buffer.c:2041 [inline]
block_write_begin+0x93/0x1e0 fs/buffer.c:2102
nilfs_write_begin+0x9c/0x110 fs/nilfs2/inode.c:261
generic_perform_write+0x2e4/0x5e0 mm/filemap.c:3772
__generic_file_write_iter+0x176/0x400 mm/filemap.c:3900
generic_file_write_iter+0xab/0x310 mm/filemap.c:3932
call_write_iter include/linux/fs.h:2186 [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
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: 0033:0x7fca03d80b59
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 14 00 00 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 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffdd1df8c28 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fca03d80b59
RDX: 000000000000002f RSI: 0000000020000040 RDI: 0000000000000004
RBP: 00007fca03d40160 R08: 0000000000000014 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fca03d401f0
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:nilfs_btree_get_nonroot_node fs/nilfs2/btree.c:418 [inline]
RIP: 0010:nilfs_btree_prepare_insert fs/nilfs2/btree.c:1077 [inline]
RIP: 0010:nilfs_btree_insert+0x6d3/0x1c10 fs/nilfs2/btree.c:1238
Code: bc 24 80 00 00 00 4c 89 f8 48 c1 e8 03 42 80 3c 28 00 74 08 4c 89 ff e8 4b 02 92 fe 4d 8b 3f 49 83 c7 28 4c 89 f8 48 c1 e8 03 <42> 80 3c 28 00 74 08 4c 89 ff e8 2e 02 92 fe 4d 8b 3f 49 83 c7 02
RSP: 0018:ffffc90003bcf4a0 EFLAGS: 00010206
RAX: 0000000000000005 RBX: 0000000000000001 RCX: 0000000000000000
RDX: ffff88807eba3a80 RSI: 0000000000000002 RDI: 0000000000000001
RBP: ffffc90003bcf630 R08: ffffffff834f80d8 R09: ffffed100571ff9b
R10: ffffed100571ff9b R11: 1ffff1100571ff9a R12: ffff888021d03480
R13: dffffc0000000000 R14: 0000000000000002 R15: 0000000000000028
FS: 000055555588c300(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055a236e64fe0 CR3: 000000007eb7c000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
0: bc 24 80 00 00 mov $0x8024,%esp
5: 00 4c 89 f8 add %cl,-0x8(%rcx,%rcx,4)
9: 48 c1 e8 03 shr $0x3,%rax
d: 42 80 3c 28 00 cmpb $0x0,(%rax,%r13,1)
12: 74 08 je 0x1c
14: 4c 89 ff mov %r15,%rdi
17: e8 4b 02 92 fe callq 0xfe920267
1c: 4d 8b 3f mov (%r15),%r15
1f: 49 83 c7 28 add $0x28,%r15
23: 4c 89 f8 mov %r15,%rax
26: 48 c1 e8 03 shr $0x3,%rax
* 2a: 42 80 3c 28 00 cmpb $0x0,(%rax,%r13,1) <-- trapping instruction
2f: 74 08 je 0x39
31: 4c 89 ff mov %r15,%rdi
34: e8 2e 02 92 fe callq 0xfe920267
39: 4d 8b 3f mov (%r15),%r15
3c: 49 83 c7 02 add $0x2,%r15


---
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.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
syzbot can test patches for this issue, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Ryusuke Konishi]

This seems to be an unfixed bug in nilfs2.

As a result of analysis using the C-reproducer, it turns out that
nilfs_btree_insert() may cause the above oops when nilfs2 reads a
corrupted disk image and a b-tree node block address translation fails
due to a DAT metadata corruption.

It's necessary to correct the error handling in the above case. I'll
take a closer look to fix this.

Ryusuke Konishi

[Ryusuke Konishi]

If nilfs2 reads a corrupted disk image and tries to reads a b-tree node
block by calling __nilfs_btree_get_block() against an invalid virtual
block address, it returns -ENOENT because conversion of the virtual
block address to a disk block address fails. However, this return
value is the same as the internal code that b-tree lookup routines
return to indicate that the block being searched does not exist, so
functions that operate on that b-tree may misbehave.

When nilfs_btree_insert() receives this spurious 'not found' code from
nilfs_btree_do_lookup(), it misunderstands that the 'not found' check
was successful and continues the insert operation using incomplete
lookup path data, causing the following crash:

general protection fault, probably for non-canonical address
0xdffffc0000000005: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]

...

RIP: 0010:nilfs_btree_get_nonroot_node fs/nilfs2/btree.c:418 [inline]
RIP: 0010:nilfs_btree_prepare_insert fs/nilfs2/btree.c:1077 [inline]
RIP: 0010:nilfs_btree_insert+0x6d3/0x1c10 fs/nilfs2/btree.c:1238
Code: bc 24 80 00 00 00 4c 89 f8 48 c1 e8 03 42 80 3c 28 00 74 08 4c 89
ff e8 4b 02 92 fe 4d 8b 3f 49 83 c7 28 4c 89 f8 48 c1 e8 03 <42> 80 3c
28 00 74 08 4c 89 ff e8 2e 02 92 fe 4d 8b 3f 49 83 c7 02

...

Call Trace:
<TASK>
nilfs_bmap_do_insert fs/nilfs2/bmap.c:121 [inline]
nilfs_bmap_insert+0x20d/0x360 fs/nilfs2/bmap.c:147
nilfs_get_block+0x414/0x8d0 fs/nilfs2/inode.c:101
__block_write_begin_int+0x54c/0x1a80 fs/buffer.c:1991
__block_write_begin fs/buffer.c:2041 [inline]
block_write_begin+0x93/0x1e0 fs/buffer.c:2102
nilfs_write_begin+0x9c/0x110 fs/nilfs2/inode.c:261
generic_perform_write+0x2e4/0x5e0 mm/filemap.c:3772
__generic_file_write_iter+0x176/0x400 mm/filemap.c:3900
generic_file_write_iter+0xab/0x310 mm/filemap.c:3932
call_write_iter include/linux/fs.h:2186 [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
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

...
</TASK>

This patch fixes the root cause of this problem by replacing the error
code that __nilfs_btree_get_block() returns on block address conversion
failure from -ENOENT to another internal code -EINVAL which means that
the b-tree metadata is corrupted.

By returning -EINVAL, it propagates without glitches, and for all
relevant b-tree operations, functions in the upper bmap layer output
an error message indicating corrupted b-tree metadata via
nilfs_bmap_convert_error(), and code -EIO will be eventually returned
as it should be.

Link: https://lkml.kernel.org/r/000000000000bd...@google.com
Reported-by: syzbot+ede796...@syzkaller.appspotmail.com
Signed-off-by: Ryusuke Konishi <konishi...@gmail.com>
Tested-by: Ryusuke Konishi <konishi...@gmail.com>
Cc: sta...@vger.kernel.org
---
Hi Andrew, please apply this bugfix.
This fixes the kernel crash above for corrupted disk images like
the one syzbot produced, and presumably fixes some unexpected WARN_ONs
on nilfs2 as well (which I will continue to investigate).

Thanks,
Ryusuke Konishi

fs/nilfs2/btree.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/fs/nilfs2/btree.c b/fs/nilfs2/btree.c
index b9d15c3df3cc..40ce92a332fe 100644
--- a/fs/nilfs2/btree.c
+++ b/fs/nilfs2/btree.c
@@ -480,9 +480,18 @@ static int __nilfs_btree_get_block(const struct nilfs_bmap *btree, __u64 ptr,
ret = nilfs_btnode_submit_block(btnc, ptr, 0, REQ_OP_READ, &bh,
&submit_ptr);
if (ret) {
- if (ret != -EEXIST)
- return ret;
- goto out_check;
+ if (likely(ret == -EEXIST))
+ goto out_check;
+ if (ret == -ENOENT) {
+ /*
+ * Block address translation failed due to invalid
+ * value of 'ptr'. In this case, return internal code
+ * -EINVAL (broken bmap) to notify bmap layer of fatal
+ * metadata corruption.
+ */
+ ret = -EINVAL;
+ }
+ return ret;
}

if (ra) {
--
2.34.1