[syzbot] [fs?] BUG: unable to handle kernel paging request in read_seqbegin

[syzbot] [fs?] BUG: unable to handle kernel paging request in read_seqbegin

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    7a19f0cc94ad Merge branch 'for-next/core' into for-kernelci
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=16514121580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=26d6221a572842ac
dashboard link: https://syzkaller.appspot.com/bug?extid=975ace299d6ba2eb1cea
compiler:       Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8
userspace arch: arm64
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16003da9580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+975ace299d6ba2eb1cea@syzkaller.appspotmail.com

Unable to handle kernel paging request at virtual address dfff800000000002
KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
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
[dfff800000000002] address between user and kernel address ranges
Internal error: Oops: 0000000096000005 [#1]  SMP
Modules linked in:
CPU: 1 UID: 0 PID: 5047 Comm: syz-executor213 Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/14/2026
pstate: 834000c5 (Nzcv daIF +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : kasan_byte_accessible+0xc/0x1c mm/kasan/generic.c:210
lr : __kasan_check_byte+0x20/0x54 mm/kasan/common.c:584
sp : ffff80009b3a6c20
x29: ffff80009b3a6c20 x28: ffff80008979a000 x27: ffff0000d7079d80
x26: a4ec800080d875c8 x25: 0000000000000000 x24: 0000000000000001
x23: 0000000000000002 x22: 0000000000000010 x21: 0000000000000010
x20: 0000000000000000 x19: ffff800080d875c8 x18: ffff80011b89c000
x17: ffff0001a4ff9e07 x16: ffff0000d7079d94 x15: ffff800080302e5c
x14: 0000000000494166 x13: 0000000000000009 x12: 0000000000000009
x11: ffff800080155740 x10: 0000000000000003 x9 : dfff800000000000
x8 : 0000000000000002 x7 : 0000000000000000 x6 : ffff800080d86228
x5 : 0000000000000000 x4 : 0000000000000001 x3 : 0000000000000002
x2 : 0000000000000000 x1 : ffff800080d875c8 x0 : 0000000000000010
Call trace:
 kasan_mem_to_shadow include/linux/kasan.h:65 [inline] (P)
 kasan_byte_accessible+0xc/0x1c mm/kasan/generic.c:210 (P)
 kasan_check_byte include/linux/kasan.h:402 [inline]
 lock_acquire+0xa4/0x320 kernel/locking/lockdep.c:5916
 seqcount_lockdep_reader_access include/linux/seqlock.h:73 [inline]
 read_seqbegin+0x6c/0x144 include/linux/seqlock.h:838
 get_fs_root_rcu fs/d_path.c:244 [inline]
 d_path+0x224/0x4dc fs/d_path.c:287
 audit_log_d_path+0xdc/0x19c kernel/audit.c:2221
 audit_log_lsm_data+0xe0/0x12d0 security/lsm_audit.c:199
 dump_common_audit_data security/lsm_audit.c:421 [inline]
 common_lsm_audit+0x1d0/0x290 security/lsm_audit.c:451
 smack_log+0x1f4/0x264 security/smack/smack_access.c:400
 smk_tskacc+0x210/0x2ac security/smack/smack_access.c:255
 smack_file_open+0x1d0/0x230 security/smack/smack_lsm.c:2078
 security_file_open+0xec/0x258 security/security.c:2739
 do_dentry_open+0x2a8/0xfbc fs/open.c:973
 vfs_open+0x44/0x2dc fs/open.c:1101
 dentry_open+0x74/0xc0 fs/open.c:1124
 ima_calc_file_hash+0x120/0x5cc security/integrity/ima/ima_crypto.c:269
 ima_collect_measurement+0x420/0x874 security/integrity/ima/ima_api.c:300
 ima_update_xattr+0x160/0x230 security/integrity/ima/ima_appraise.c:617
 ima_check_last_writer security/integrity/ima/ima_main.c:227 [inline]
 ima_file_free+0x40c/0x528 security/integrity/ima/ima_main.c:251
 security_file_release+0x84/0x148 security/security.c:2424
 __fput+0x2c4/0x74c fs/file_table.c:506
 ____fput+0x20/0x30 fs/file_table.c:541
 task_work_run+0x1cc/0x25c kernel/task_work.c:233
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x58c/0x1a74 kernel/exit.c:986
 do_group_exit+0x198/0x238 kernel/exit.c:1129
 __do_sys_exit_group kernel/exit.c:1140 [inline]
 __se_sys_exit_group kernel/exit.c:1138 [inline]
 pid_child_should_wake+0x0/0x104 kernel/exit.c:1138
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0x19c/0x23c arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
 el0_svc+0x60/0x1d8 arch/arm64/kernel/entry-common.c:796
 el0t_64_sync_handler+0x44/0x104 arch/arm64/kernel/entry-common.c:815
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:606
Code: 17ffffec d343fc08 d2d00009 f2fbffe9 (38696908) 
---[ end trace 0000000000000000 ]---
----------------
Code disassembly (best guess):
   0:	17ffffec 	b	0xffffffffffffffb0
   4:	d343fc08 	lsr	x8, x0, #3
   8:	d2d00009 	mov	x9, #0x800000000000        	// #140737488355328
   c:	f2fbffe9 	movk	x9, #0xdfff, lsl #48
* 10:	38696908 	ldrb	w8, [x8, x9] <-- trapping instruction


---
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Forwarded: fs/d_path: Prevent NULL pointer dereference in get_fs_root_rcu()

[syzbot]

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***

Subject: fs/d_path: Prevent NULL pointer dereference in get_fs_root_rcu()
Author: neganhat@gmail.com

#syz test: upstream 7a19f0cc94ad