[syzbot] [btrfs?] general protection fault in write_all_supers

[syzbot] [btrfs?] general protection fault in write_all_supers

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    b831f83e40a2 Merge tag 'bpf-6.11-rc7' of git://git.kernel...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1197909f980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=660f6eb11f9c7dc5
dashboard link: https://syzkaller.appspot.com/bug?extid=56360f93efa90ff15870
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=14ccaffb980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=107d03c7980000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7bc7510fe41f/non_bootable_disk-b831f83e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ab02bf22935d/vmlinux-b831f83e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c1101078451d/bzImage-b831f83e.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/6d79e1e6aae6/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+56360f93efa90ff15870@syzkaller.appspotmail.com

BTRFS info (device loop0 state MCS): disabling free space tree
BTRFS info (device loop0 state MCS): clearing compat-ro feature flag for FREE_SPACE_TREE (0x1)
BTRFS info (device loop0 state MCS): clearing compat-ro feature flag for FREE_SPACE_TREE_VALID (0x2)
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000003: 0000 [#1] PREEMPT SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
CPU: 0 UID: 0 PID: 5101 Comm: syz-executor285 Not tainted 6.11.0-rc6-syzkaller-00183-gb831f83e40a2 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:backup_super_roots fs/btrfs/disk-io.c:1691 [inline]
RIP: 0010:write_all_supers+0x97a/0x40f0 fs/btrfs/disk-io.c:4041
Code: 00 00 00 48 89 d8 48 c1 e8 03 42 0f b6 04 28 84 c0 0f 85 8a 34 00 00 44 88 33 48 8b 5c 24 10 48 83 c3 18 49 89 df 49 c1 ef 03 <43> 80 3c 2f 00 74 08 48 89 df e8 17 b6 4b fe 48 89 5c 24 10 48 8b
RSP: 0018:ffffc90002d3f040 EFLAGS: 00010206
RAX: 0000000000000000 RBX: 0000000000000018 RCX: 0000000000000000
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffff888035eeaa80
RBP: ffffc90002d3f3f0 R08: ffff88803d48806b R09: 1ffff11007a9100d
R10: dffffc0000000000 R11: ffffed1007a9100e R12: dffffc0000000000
R13: dffffc0000000000 R14: 0000000000000000 R15: 0000000000000003
FS:  0000555594a77380(0000) GS:ffff88801fe00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000056349cf20668 CR3: 000000003f9f4000 CR4: 0000000000350ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 btrfs_commit_transaction+0x1eae/0x3740 fs/btrfs/transaction.c:2530
 btrfs_delete_free_space_tree+0x383/0x730 fs/btrfs/free-space-tree.c:1312
 btrfs_start_pre_rw_mount+0xf28/0x1300 fs/btrfs/disk-io.c:3012
 btrfs_remount_rw fs/btrfs/super.c:1309 [inline]
 btrfs_reconfigure+0xae6/0x2d40 fs/btrfs/super.c:1534
 btrfs_reconfigure_for_mount fs/btrfs/super.c:2020 [inline]
 btrfs_get_tree_subvol fs/btrfs/super.c:2079 [inline]
 btrfs_get_tree+0x918/0x1920 fs/btrfs/super.c:2115
 vfs_get_tree+0x90/0x2b0 fs/super.c:1800
 do_new_mount+0x2be/0xb40 fs/namespace.c:3472
 do_mount fs/namespace.c:3812 [inline]
 __do_sys_mount fs/namespace.c:4020 [inline]
 __se_sys_mount+0x2d6/0x3c0 fs/namespace.c:3997
 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: 0033:0x7fb7b8916e99
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 17 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe5c5484c8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0030656c69662f2e RCX: 00007fb7b8916e99
RDX: 0000000020000280 RSI: 0000000020000180 RDI: 0000000020000100
RBP: 00007fb7b89905f0 R08: 0000000000000000 R09: 0000555594a784c0
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffe5c5484f0
R13: 00007ffe5c548718 R14: 431bde82d7b634db R15: 00007fb7b896003b
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:backup_super_roots fs/btrfs/disk-io.c:1691 [inline]
RIP: 0010:write_all_supers+0x97a/0x40f0 fs/btrfs/disk-io.c:4041
Code: 00 00 00 48 89 d8 48 c1 e8 03 42 0f b6 04 28 84 c0 0f 85 8a 34 00 00 44 88 33 48 8b 5c 24 10 48 83 c3 18 49 89 df 49 c1 ef 03 <43> 80 3c 2f 00 74 08 48 89 df e8 17 b6 4b fe 48 89 5c 24 10 48 8b
RSP: 0018:ffffc90002d3f040 EFLAGS: 00010206
RAX: 0000000000000000 RBX: 0000000000000018 RCX: 0000000000000000
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffff888035eeaa80
RBP: ffffc90002d3f3f0 R08: ffff88803d48806b R09: 1ffff11007a9100d
R10: dffffc0000000000 R11: ffffed1007a9100e R12: dffffc0000000000
R13: dffffc0000000000 R14: 0000000000000000 R15: 0000000000000003
FS:  0000555594a77380(0000) GS:ffff88801fe00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f731263196e CR3: 000000003f9f4000 CR4: 0000000000350ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	00 00                	add    %al,(%rax)
   2:	00 48 89             	add    %cl,-0x77(%rax)
   5:	d8 48 c1             	fmuls  -0x3f(%rax)
   8:	e8 03 42 0f b6       	call   0xb60f4210
   d:	04 28                	add    $0x28,%al
   f:	84 c0                	test   %al,%al
  11:	0f 85 8a 34 00 00    	jne    0x34a1
  17:	44 88 33             	mov    %r14b,(%rbx)
  1a:	48 8b 5c 24 10       	mov    0x10(%rsp),%rbx
  1f:	48 83 c3 18          	add    $0x18,%rbx
  23:	49 89 df             	mov    %rbx,%r15
  26:	49 c1 ef 03          	shr    $0x3,%r15
* 2a:	43 80 3c 2f 00       	cmpb   $0x0,(%r15,%r13,1) <-- trapping instruction
  2f:	74 08                	je     0x39
  31:	48 89 df             	mov    %rbx,%rdi
  34:	e8 17 b6 4b fe       	call   0xfe4bb650
  39:	48 89 5c 24 10       	mov    %rbx,0x10(%rsp)
  3e:	48                   	rex.W
  3f:	8b                   	.byte 0x8b


---
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#syz test: git://repo/address.git branch-or-commit-hash
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#syz undup

Re: [syzbot] [btrfs?] general protection fault in write_all_supers

[Lizhi Xu]

if we have IGNOREDATACSUMS then don't need to backup csum root 

#syz test

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index a6f5441e62d1..415ad3b07032 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1679,7 +1679,6 @@ static void backup_super_roots(struct btrfs_fs_info *info)
 
 	if (!btrfs_fs_compat_ro(info, BLOCK_GROUP_TREE)) {
 		struct btrfs_root *extent_root = btrfs_extent_root(info, 0);
-		struct btrfs_root *csum_root = btrfs_csum_root(info, 0);
 
 		btrfs_set_backup_extent_root(root_backup,
 					     extent_root->node->start);
@@ -1688,11 +1687,15 @@ static void backup_super_roots(struct btrfs_fs_info *info)
 		btrfs_set_backup_extent_root_level(root_backup,
 					btrfs_header_level(extent_root->node));
 
-		btrfs_set_backup_csum_root(root_backup, csum_root->node->start);
-		btrfs_set_backup_csum_root_gen(root_backup,
-					       btrfs_header_generation(csum_root->node));
-		btrfs_set_backup_csum_root_level(root_backup,
-						 btrfs_header_level(csum_root->node));
+		if (!btrfs_test_opt(info, IGNOREDATACSUMS)) {
+			struct btrfs_root *csum_root = btrfs_csum_root(info, 0);
+
+			btrfs_set_backup_csum_root(root_backup, csum_root->node->start);
+			btrfs_set_backup_csum_root_gen(root_backup,
+						       btrfs_header_generation(csum_root->node));
+			btrfs_set_backup_csum_root_level(root_backup,
+							 btrfs_header_level(csum_root->node));
+		}
 	}
 
 	/*

Re: [syzbot] [btrfs?] general protection fault in write_all_supers

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+56360f93efa90ff15870@syzkaller.appspotmail.com
Tested-by: syzbot+56360f93efa90ff15870@syzkaller.appspotmail.com

Tested on:

commit:         b7718454 Merge tag 'pci-v6.11-fixes-4' of git://git.ke..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=136150a9980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=61d235cb8d15001c
dashboard link: https://syzkaller.appspot.com/bug?extid=56360f93efa90ff15870
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=1731349f980000

Note: testing is done by a robot and is best-effort only.

Re: [syzbot] [btrfs?] general protection fault in write_all_supers

[Qu Wenruo]

在 2024/9/14 16:11, Lizhi Xu 写道:
> if we have IGNOREDATACSUMS then don't need to backup csum root
>
> #syz test
>
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index a6f5441e62d1..415ad3b07032 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -1679,7 +1679,6 @@ static void backup_super_roots(struct btrfs_fs_info *info)
>
>   	if (!btrfs_fs_compat_ro(info, BLOCK_GROUP_TREE)) {
>   		struct btrfs_root *extent_root = btrfs_extent_root(info, 0);
> -		struct btrfs_root *csum_root = btrfs_csum_root(info, 0);
>
>   		btrfs_set_backup_extent_root(root_backup,
>   					     extent_root->node->start);
> @@ -1688,11 +1687,15 @@ static void backup_super_roots(struct btrfs_fs_info *info)
>   		btrfs_set_backup_extent_root_level(root_backup,
>   					btrfs_header_level(extent_root->node));
>
> -		btrfs_set_backup_csum_root(root_backup, csum_root->node->start);
> -		btrfs_set_backup_csum_root_gen(root_backup,
> -					       btrfs_header_generation(csum_root->node));
> -		btrfs_set_backup_csum_root_level(root_backup,
> -						 btrfs_header_level(csum_root->node));
> +		if (!btrfs_test_opt(info, IGNOREDATACSUMS)) {

This doesn't looks sane to me.

IGNOREDATACSUMS is only set with rescue=idatacsums mount option, which
relies the fs to be fully RO (not any writeback, including any log
replay), and it's not allowed to be remounted RW.

If we're hitting a missing csum root, and IGNOREDATACSUMS is applied
here, I'm wondering why we're even writing a super block.

This looks like a deeper problem, not just a NULL pointer dereference,
but some logic problem.

Thanks,
Qu

> +			struct btrfs_root *csum_root = btrfs_csum_root(info, 0);
> +
> +			btrfs_set_backup_csum_root(root_backup, csum_root->node->start);
> +			btrfs_set_backup_csum_root_gen(root_backup,
> +						       btrfs_header_generation(csum_root->node));
> +			btrfs_set_backup_csum_root_level(root_backup,
> +							 btrfs_header_level(csum_root->node));
> +		}
>   	}
>
>   	/*
>