[syzbot] [ext4?] kernel BUG in ext4_update_inline_data

[syzbot] [ext4?] kernel BUG in ext4_update_inline_data

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    772b78c2abd8 Merge tag 'sched_urgent_for_v6.16_rc5' of git..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1747ef70580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=930b74448cb4593a
dashboard link: https://syzkaller.appspot.com/bug?extid=544248a761451c0df72f
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=120e828c580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=160e828c580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-772b78c2.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8a1257ea2c00/vmlinux-772b78c2.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ff01d2c78ebd/bzImage-772b78c2.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/f97118969515/mount_0.gz
  fsck result: OK (log: https://syzkaller.appspot.com/x/fsck.log?x=1581628c580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+544248a761451c0df72f@syzkaller.appspotmail.com

EXT4-fs (loop0): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: writeback.
fscrypt: AES-256-XTS using implementation "xts-aes-aesni-avx"
loop0: detected capacity change from 512 to 64
------------[ cut here ]------------
kernel BUG at fs/ext4/inline.c:357!
Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI
CPU: 0 UID: 0 PID: 5499 Comm: syz.0.16 Not tainted 6.16.0-rc4-syzkaller-00348-g772b78c2abd8 #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:ext4_update_inline_data+0x4e8/0x4f0 fs/ext4/inline.c:357
Code: ff ff ff 48 8b 4c 24 18 80 e1 07 fe c1 38 c1 0f 8c 32 ff ff ff 48 8b 7c 24 18 e8 33 59 b1 ff e9 23 ff ff ff e8 e9 d5 4d ff 90 <0f> 0b 66 0f 1f 44 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 0018:ffffc90002abf4a0 EFLAGS: 00010293
RAX: ffffffff82725017 RBX: ffff8880123cf558 RCX: ffff88800020c880
RDX: 0000000000000000 RSI: 00000000ffffffc3 RDI: 0000000000000000
RBP: ffffc90002abf5f0 R08: ffff88800020c880 R09: 0000000000000002
R10: 00000000ffffffc3 R11: 0000000000000000 R12: 00000000ffffffc3
R13: 000000000000004a R14: ffffc90002abf500 R15: ffffc90002abf528
FS:  0000555558bce500(0000) GS:ffff88808d21d000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055795b748950 CR3: 000000003f98a000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 ext4_prepare_inline_data+0x141/0x1d0 fs/ext4/inline.c:415
 ext4_generic_write_inline_data+0x207/0xc90 fs/ext4/inline.c:692
 ext4_try_to_write_inline_data+0x80/0xa0 fs/ext4/inline.c:763
 ext4_write_begin+0x2d8/0x1680 fs/ext4/inode.c:1281
 generic_perform_write+0x2c7/0x910 mm/filemap.c:4112
 ext4_buffered_write_iter+0xce/0x3a0 fs/ext4/file.c:299
 ext4_file_write_iter+0x298/0x1bc0 fs/ext4/file.c:-1
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x548/0xa90 fs/read_write.c:686
 ksys_write+0x145/0x250 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f32a778e929
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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fffd1fdeb38 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f32a79b5fa0 RCX: 00007f32a778e929
RDX: 000000000000004a RSI: 0000000000000000 RDI: 0000000000000007
RBP: 00007f32a7810b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f32a79b5fa0 R14: 00007f32a79b5fa0 R15: 0000000000000003
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:ext4_update_inline_data+0x4e8/0x4f0 fs/ext4/inline.c:357
Code: ff ff ff 48 8b 4c 24 18 80 e1 07 fe c1 38 c1 0f 8c 32 ff ff ff 48 8b 7c 24 18 e8 33 59 b1 ff e9 23 ff ff ff e8 e9 d5 4d ff 90 <0f> 0b 66 0f 1f 44 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 0018:ffffc90002abf4a0 EFLAGS: 00010293
RAX: ffffffff82725017 RBX: ffff8880123cf558 RCX: ffff88800020c880
RDX: 0000000000000000 RSI: 00000000ffffffc3 RDI: 0000000000000000
RBP: ffffc90002abf5f0 R08: ffff88800020c880 R09: 0000000000000002
R10: 00000000ffffffc3 R11: 0000000000000000 R12: 00000000ffffffc3
R13: 000000000000004a R14: ffffc90002abf500 R15: ffffc90002abf528
FS:  0000555558bce500(0000) GS:ffff88808d21d000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000563842271138 CR3: 000000003f98a000 CR4: 0000000000352ef0


---
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[syzbot] [ext4?] kernel BUG in ext4_update_inline_data

[Moon Hee Lee]

[-- Attachment #1: Type: text/plain, Size: 10 bytes --]

#syz test

[-- Attachment #2: 0001-ext4-bail-out-when-INLINE_DATA_FL-lacks-system.data-.patch --]
[-- Type: text/x-patch, Size: 2885 bytes --]

From 4c910ac989e7a6d97565a67677a1ee88e2d1a9ad Mon Sep 17 00:00:00 2001
From: Moon Hee Lee <moonhee.lee.ca@gmail.com>
Date: Thu, 10 Jul 2025 00:36:59 -0700
Subject: [PATCH] ext4: bail out when INLINE_DATA_FL lacks system.data xattr

A syzbot fuzzed image triggered a BUG_ON in ext4_update_inline_data()
when an inode had the INLINE_DATA_FL flag set but was missing the
system.data extended attribute.

ext4_prepare_inline_data() now checks for the presence of that xattr
and returns -EFSCORRUPTED if it is missing, preventing corrupted inodes
from reaching the update path and triggering a crash.

Proof from e2fsck on the fuzzed image:

    $ e2fsck -fn mount_0
    e2fsck 1.47.0 (5-Feb-2023)
    One or more block group descriptor checksums are invalid.  Fix? no

    Group descriptor 0 checksum is 0x8245, should be 0x353a.  IGNORED.
    Pass 1: Checking inodes, blocks, and sizes
    Inode 12 has INLINE_DATA_FL flag but extended attribute not found.  Truncate? no

    Inode 16, i_blocks is 3298534883346, should be 18.  Fix? no

    Inode 17, i_blocks is 17592186044416, should be 0.  Fix? no

    Pass 2: Checking directory structure
    Symlink /file0/file1 (inode #14) is invalid.
    Clear? no

    Entry 'file1' in /file0 (12) has an incorrect filetype (was 7, should be 0).
    Fix? no

    Directory inode 11, block #5, offset 0: directory corrupted
    Salvage? no

    e2fsck: aborted

    syzkaller: ********** WARNING: Filesystem still has errors **********

Signed-off-by: Moon Hee Lee <moonhee.lee.ca@gmail.com>
---
 fs/ext4/inline.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
index a1bbcdf40824..d9dcb0b09e5c 100644
--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -399,6 +399,13 @@ static int ext4_update_inline_data(handle_t *handle, struct inode *inode,
 static int ext4_prepare_inline_data(handle_t *handle, struct inode *inode,
 				    loff_t len)
 {
+	struct ext4_xattr_ibody_find is = {
+		.s = { .not_found = -ENODATA, },
+	};
+	struct ext4_xattr_info i = {
+		.name_index = EXT4_XATTR_INDEX_SYSTEM,
+		.name = EXT4_XATTR_SYSTEM_DATA,
+	};
 	int ret, size, no_expand;
 	struct ext4_inode_info *ei = EXT4_I(inode);
 
@@ -409,6 +416,19 @@ static int ext4_prepare_inline_data(handle_t *handle, struct inode *inode,
 	if (size < len)
 		return -ENOSPC;
 
+	ret = ext4_get_inode_loc(inode, &is.iloc);
+	if (ret)
+		goto out;
+
+	ret = ext4_xattr_ibody_find(inode, &i, &is);
+	if (ret)
+		goto out;
+
+	if (is.s.not_found) {
+		ret = -EFSCORRUPTED;
+		goto out;
+	}
+
 	ext4_write_lock_xattr(inode, &no_expand);
 
 	if (ei->i_inline_off)
@@ -417,6 +437,8 @@ static int ext4_prepare_inline_data(handle_t *handle, struct inode *inode,
 		ret = ext4_create_inline_data(handle, inode, len);
 
 	ext4_write_unlock_xattr(inode, &no_expand);
+out:
+	brelse(is.iloc.bh);
 	return ret;
 }
 
-- 
2.43.0

Re: [syzbot] [ext4?] kernel BUG in ext4_update_inline_data

[syzbot]

Hello,

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

Reported-by: syzbot+544248a761451c0df72f@syzkaller.appspotmail.com
Tested-by: syzbot+544248a761451c0df72f@syzkaller.appspotmail.com

Tested on:

commit:         8c2e52eb eventpoll: don't decrement ep refcount while ..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14ff7582580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b309c907eaab29da
dashboard link: https://syzkaller.appspot.com/bug?extid=544248a761451c0df72f
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
patch:          https://syzkaller.appspot.com/x/patch.diff?x=15ef7582580000

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