Re: [syzbot] [bcachefs?] UBSAN: shift-out-of-bounds in bch2_alloc_to_text

[Hongbo Li <lihongbo22@huawei.com>]

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#syz test: 
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 
c964ced77262

On 2024/10/21 14:44, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    c964ced77262 Merge tag 'for-linus' of git://git.kernel.org..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=12d9745f980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=cfbd94c114a3d407
> dashboard link: https://syzkaller.appspot.com/bug?extid=7f45fa9805c40db3f108
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12637887980000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12a1e830580000
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-c964ced7.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/e937ef58569a/vmlinux-c964ced7.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/f1df9880ca4b/bzImage-c964ced7.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/00439b875347/mount_0.gz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+7f45fa9805c40db3f108@syzkaller.appspotmail.com
> 
> bcachefs (loop0): fatal error - emergency read only
> bcachefs (loop0): insufficient writeable journal devices available: have 0, need 1
> rw journal devs: loop0
> ------------[ cut here ]------------
> UBSAN: shift-out-of-bounds in fs/bcachefs/alloc_background.h:165:13
> shift exponent 129 is too large for 32-bit type 'unsigned int'
> CPU: 0 UID: 0 PID: 5104 Comm: syz-executor159 Not tainted 6.12.0-rc3-syzkaller-00087-gc964ced77262 #0
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> Call Trace:
>   <TASK>
>   __dump_stack lib/dump_stack.c:94 [inline]
>   dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
>   ubsan_epilogue lib/ubsan.c:231 [inline]
>   __ubsan_handle_shift_out_of_bounds+0x3c8/0x420 lib/ubsan.c:468
>   data_type_movable fs/bcachefs/alloc_background.h:165 [inline]
>   alloc_lru_idx_fragmentation fs/bcachefs/alloc_background.h:171 [inline]
>   bch2_alloc_to_text+0xc79/0xce0 fs/bcachefs/alloc_background.c:369
>   __bch2_bkey_fsck_err+0x1c8/0x280 fs/bcachefs/error.c:454
>   bch2_alloc_v4_validate+0x931/0xef0 fs/bcachefs/alloc_background.c:259
>   bch2_btree_node_read_done+0x3e7e/0x5e90 fs/bcachefs/btree_io.c:1223
>   btree_node_read_work+0x68b/0x1260 fs/bcachefs/btree_io.c:1327
>   bch2_btree_node_read+0x2433/0x2a10
>   __bch2_btree_root_read fs/bcachefs/btree_io.c:1753 [inline]
>   bch2_btree_root_read+0x617/0x7a0 fs/bcachefs/btree_io.c:1775
>   read_btree_roots+0x296/0x840 fs/bcachefs/recovery.c:524
>   bch2_fs_recovery+0x2585/0x39c0 fs/bcachefs/recovery.c:854
>   bch2_fs_start+0x356/0x5b0 fs/bcachefs/super.c:1036
>   bch2_fs_get_tree+0xd68/0x1710 fs/bcachefs/fs.c:2174
>   vfs_get_tree+0x90/0x2b0 fs/super.c:1800
>   do_new_mount+0x2be/0xb40 fs/namespace.c:3507
>   do_mount fs/namespace.c:3847 [inline]
>   __do_sys_mount fs/namespace.c:4055 [inline]
>   __se_sys_mount+0x2d6/0x3c0 fs/namespace.c:4032
>   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>   do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f7b61a11dea
> Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb a6 e8 5e 04 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 b8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffff7f9a888 EFLAGS: 00000282 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffda RBX: 00007ffff7f9a8a0 RCX: 00007f7b61a11dea
> RDX: 00000000200058c0 RSI: 0000000020000100 RDI: 00007ffff7f9a8a0
> RBP: 0000000000000004 R08: 00007ffff7f9a8e0 R09: 00000000000058c6
> R10: 0000000000000000 R11: 0000000000000282 R12: 0000000000000000
> R13: 00007ffff7f9a8e0 R14: 0000000000000003 R15: 0000000001000000
>   </TASK>
> ---[ end trace ]---
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
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> 
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> 
> If you want syzbot to run the reproducer, reply with:
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> 

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From 17fd366091d104702af5b0699ac73b06d0b57619 Mon Sep 17 00:00:00 2001
From: Hongbo Li <lihongbo22@huawei.com>
Date: Mon, 21 Oct 2024 15:35:09 +0800
Subject: [PATCH] bcachefs: Fix shift-out-of-bounds in bch2_alloc_to_text

The syzbot found the following issue:
```
------------[ cut here ]------------
UBSAN: shift-out-of-bounds in fs/bcachefs/alloc_background.h:165:13
shift exponent 129 is too large for 32-bit type 'unsigned int'

Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 ubsan_epilogue lib/ubsan.c:231 [inline]
 __ubsan_handle_shift_out_of_bounds+0x3c8/0x420 lib/ubsan.c:468
 data_type_movable fs/bcachefs/alloc_background.h:165 [inline]
 alloc_lru_idx_fragmentation fs/bcachefs/alloc_background.h:171 [inline]
 bch2_alloc_to_text+0xc79/0xce0 fs/bcachefs/alloc_background.c:369
 __bch2_bkey_fsck_err+0x1c8/0x280 fs/bcachefs/error.c:454
 bch2_alloc_v4_validate+0x931/0xef0 fs/bcachefs/alloc_background.c:259
 ...
```

In bch2_alloc_v4_validate, bcachefs doesn't check the invalid
data_type in switch-case. And this will cause shift-out-of-bounds
error for invalid data_type. This can be easily avoided by adding
the default branch in switch statement for handling the data_type.

Reported-by: syzbot+7f45fa9805c40db3f108@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=7f45fa9805c40db3f108
Fixes: 71aba590297e ("bcachefs: Always check alloc data type")
Signed-off-by: Hongbo Li <lihongbo22@huawei.com>
---
 fs/bcachefs/alloc_background.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/bcachefs/alloc_background.c b/fs/bcachefs/alloc_background.c
index 6e161f8ffe8d..09ff41cac5f8 100644
--- a/fs/bcachefs/alloc_background.c
+++ b/fs/bcachefs/alloc_background.c
@@ -314,6 +314,10 @@ int bch2_alloc_v4_validate(struct bch_fs *c, struct bkey_s_c k,
 		break;
 	case BCH_DATA_stripe:
 		break;
+	default:
+		bkey_fsck_err_on(true, c, alloc_key_data_type_bad,
+				 "unknown data type %u", a.data_type);
+		break;
 	}
 fsck_err:
 	return ret;
-- 
2.34.1