Re: [syzbot] [ext4?] general protection fault in __block_commit_write

[syzbot <syzbot+18df508cf00a0598d9a6@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
BUG: unable to handle kernel paging request in __block_commit_write

Unable to handle kernel paging request at virtual address dfff800000000004
KASAN: null-ptr-deref in range [0x0000000000000020-0x0000000000000027]
Mem abort info:
  ESR = 0x0000000096000005
  EC = 0x25: DABT (current EL), IL = 32 bits
  SET = 0, FnV = 0
  EA = 0, S1PTW = 0
  FSC = 0x05: level 1 translation fault
Data abort info:
  ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000
  CM = 0, WnR = 0, TnD = 0, TagAccess = 0
  GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[dfff800000000004] address between user and kernel address ranges
Internal error: Oops: 0000000096000005 [#1] PREEMPT SMP
Modules linked in:
CPU: 1 PID: 10062 Comm: syz-executor Not tainted 6.10.0-rc6-syzkaller-g22a40d14b572 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : __block_commit_write+0x64/0x2b0 fs/buffer.c:2190
lr : __block_commit_write+0x3c/0x2b0 fs/buffer.c:2183
sp : ffff800098507600
x29: ffff800098507610 x28: dfff800000000000 x27: ffff0000dfe252b0
x26: 0000000000000000 x25: dfff800000000000 x24: dfff800000000000
x23: fffffdffc3a7e460 x22: 0000000000000020 x21: 0000000000000020
x20: 0000000000000040 x19: fffffdffc3a7e440 x18: 1fffe000367b23de
x17: ffff80008efed000 x16: ffff80008af20c64 x15: 00000000200000c0
x14: 1fffe0001d3f2204 x13: 0000000000000000 x12: 0000000000000000
x11: 0000000000000001 x10: 0000000000ff0100 x9 : 0000000000000000
x8 : 0000000000000004 x7 : 0000000000000000 x6 : 0000000000000000
x5 : fffffdffc3a7e440 x4 : 0000000000000020 x3 : 0000000000000020
x2 : 0000000000000040 x1 : 0000000000000020 x0 : fffffdffc3a7e440
Call trace:
 __block_commit_write+0x64/0x2b0 fs/buffer.c:2190
 block_write_end+0xb4/0x104 fs/buffer.c:2276
 ext4_da_do_write_end fs/ext4/inode.c:2952 [inline]
 ext4_da_write_end+0x2c4/0xa40 fs/ext4/inode.c:3025
 generic_perform_write+0x394/0x588 mm/filemap.c:4026
 ext4_buffered_write_iter+0x2c0/0x4ec fs/ext4/file.c:299
 ext4_file_write_iter+0x188/0x1780
 new_sync_write fs/read_write.c:497 [inline]
 vfs_write+0x828/0xc78 fs/read_write.c:590
 ksys_write+0x15c/0x26c fs/read_write.c:643
 __do_sys_write fs/read_write.c:655 [inline]
 __se_sys_write fs/read_write.c:652 [inline]
 __arm64_sys_write+0x7c/0x90 fs/read_write.c:652
 __invoke_syscall arch/arm64/kernel/syscall.c:34 [inline]
 invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:48
 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:131
 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:150
 el0_svc+0x54/0x168 arch/arm64/kernel/entry-common.c:712
 el0t_64_sync_handler+0x84/0xfc arch/arm64/kernel/entry-common.c:730
 el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:598
Code: 97f8507d f94002da 91008356 d343fec8 (38796908) 
---[ end trace 0000000000000000 ]---
----------------
Code disassembly (best guess):
   0:	97f8507d 	bl	0xffffffffffe141f4
   4:	f94002da 	ldr	x26, [x22]
   8:	91008356 	add	x22, x26, #0x20
   c:	d343fec8 	lsr	x8, x22, #3
* 10:	38796908 	ldrb	w8, [x8, x25] <-- trapping instruction


Tested on:

commit:         22a40d14 Linux 6.10-rc6
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=135d71c6980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f85e95b525c28b48
dashboard link: https://syzkaller.appspot.com/bug?extid=18df508cf00a0598d9a6
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm64

Note: no patches were applied.