Re: [syzbot] [fs?] [efi?] BUG: unable to handle kernel paging request in alloc_fs_context

[syzbot <syzbot+52cd651546d11d2af06b@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 alloc_fs_context

Bluetooth: hci0: Opcode 0x0c1a failed: -4
efivarfs: resyncing variable state
Unable to handle kernel paging request at virtual address dfff800000000005
KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
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
[dfff800000000005] address between user and kernel address ranges
Internal error: Oops: 0000000096000005 [#1]  SMP
Modules linked in:
CPU: 1 UID: 0 PID: 7789 Comm: syz.0.174 Not tainted 6.15.0-rc7-syzkaller-gd7fa1af5b33e #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : alloc_fs_context+0x1b4/0x76c fs/fs_context.c:294
lr : __lse_atomic64_add arch/arm64/include/asm/atomic_lse.h:134 [inline]
lr : arch_atomic64_add arch/arm64/include/asm/atomic.h:67 [inline]
lr : raw_atomic64_add include/linux/atomic/atomic-arch-fallback.h:2672 [inline]
lr : raw_atomic_long_add include/linux/atomic/atomic-long.h:121 [inline]
lr : atomic_long_add include/linux/atomic/atomic-instrumented.h:3261 [inline]
lr : get_cred_many include/linux/cred.h:203 [inline]
lr : get_cred include/linux/cred.h:218 [inline]
lr : alloc_fs_context+0x150/0x76c fs/fs_context.c:293
sp : ffff80009b8c7440
x29: ffff80009b8c7470 x28: dfff800000000000 x27: ffff0000cbd6a758
x26: 0000000000000028 x25: ffff0000d6dd9cc8 x24: ffff80008fba8a20
x23: 0000000000000000 x22: ffff0000d6dd9c98 x21: ffff0000cbd69e80
x20: 0000000000000000 x19: ffff0000d6dd9c00 x18: ffff800090e6c920
x17: ffff800092f39000 x16: ffff80008adbda98 x15: 0000000000000001
x14: 1fffe00019683fa0 x13: 0000000000000000 x12: 0000000000000000
x11: ffff600019683fa1 x10: 0000000000ff0100 x9 : 0000000000000000
x8 : 0000000000000005 x7 : ffff80008020cba8 x6 : ffff8000803f41e0
x5 : ffff0000d95932c8 x4 : ffff80009b8c71f8 x3 : ffff800080dfffa8
x2 : 0000000000000001 x1 : 0000000000000008 x0 : 0000000000000001
Call trace:
 alloc_fs_context+0x1b4/0x76c fs/fs_context.c:294 (P)
 fs_context_for_mount+0x34/0x44 fs/fs_context.c:332
 vfs_kern_mount+0x38/0x178 fs/namespace.c:1309
 efivarfs_pm_notify+0x1c4/0x4b4 fs/efivarfs/super.c:529
 notifier_call_chain+0x1b8/0x4e4 kernel/notifier.c:85
 blocking_notifier_call_chain+0x70/0xa0 kernel/notifier.c:380
 pm_notifier_call_chain+0x2c/0x3c kernel/power/main.c:109
 snapshot_release+0x104/0x1c4 kernel/power/user.c:125
 __fput+0x340/0x75c fs/file_table.c:465
 ____fput+0x20/0x58 fs/file_table.c:493
 task_work_run+0x1dc/0x260 kernel/task_work.c:227
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x4e8/0x1998 kernel/exit.c:953
 do_group_exit+0x194/0x22c kernel/exit.c:1102
 get_signal+0x11dc/0x12f8 kernel/signal.c:3034
 do_signal+0x274/0x4438 arch/arm64/kernel/signal.c:1615
 do_notify_resume+0xac/0x1ec arch/arm64/kernel/entry-common.c:148
 exit_to_user_mode_prepare arch/arm64/kernel/entry-common.c:169 [inline]
 exit_to_user_mode arch/arm64/kernel/entry-common.c:178 [inline]
 el0_svc+0xb4/0x17c arch/arm64/kernel/entry-common.c:768
 el0t_64_sync_handler+0x78/0x108 arch/arm64/kernel/entry-common.c:786
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:600
Code: 97f8aa83 f9400368 9100a11a d343ff48 (387c6908) 
---[ end trace 0000000000000000 ]---
----------------
Code disassembly (best guess):
   0:	97f8aa83 	bl	0xffffffffffe2aa0c
   4:	f9400368 	ldr	x8, [x27]
   8:	9100a11a 	add	x26, x8, #0x28
   c:	d343ff48 	lsr	x8, x26, #3
* 10:	387c6908 	ldrb	w8, [x8, x28] <-- trapping instruction


Tested on:

commit:         d7fa1af5 Merge branch 'for-next/core' into for-kernelci
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=1689aad4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=89c13de706fbf07a
dashboard link: https://syzkaller.appspot.com/bug?extid=52cd651546d11d2af06b
compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
userspace arch: arm64

Note: no patches were applied.