Re: [syzbot] [usb?] KASAN: slab-use-after-free Read in ep_open

[syzbot]

Hello,

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

Unable to handle kernel paging request at virtual address dfff800000000003
KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
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
[dfff800000000003] address between user and kernel address ranges
Internal error: Oops: 0000000096000005 [#1]  SMP
Modules linked in:
CPU: 0 UID: 0 PID: 5115 Comm: syz-executor Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/02/2026
pstate: 234000c5 (nzCv daIF +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : kasan_byte_accessible+0x10/0x20 mm/kasan/generic.c:210
lr : __kasan_check_byte+0x20/0x54 mm/kasan/common.c:573
sp : ffff800092f37660
x29: ffff800092f37660 x28: ffff800088b0a000 x27: ffff0000c79d57c0
x26: a6d980008690513c x25: 0000000000000000 x24: 0000000000000001
x23: 0000000000000000 x22: 0000000000000018 x21: 0000000000000018
x20: 0000000000000000 x19: ffff80008690513c x18: 0000000000000000
x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
x14: 00000000ffff8000 x13: 0000000000000001 x12: 0000000000000000
x11: ffff800080156ee8 x10: 0000000000000003 x9 : dfff800000000000
x8 : 0000000000000003 x7 : 0000000000000000 x6 : ffff8000836dc930
x5 : 0000000000000000 x4 : 0000000000000001 x3 : 0000000000000000
x2 : 0000000000000000 x1 : ffff80008690513c x0 : 0000000000000018
Call trace:
 kasan_mem_to_shadow include/linux/kasan.h:65 [inline] (P)
 kasan_byte_accessible+0x10/0x20 mm/kasan/generic.c:210 (P)
 kasan_check_byte include/linux/kasan.h:402 [inline]
 lock_acquire+0xa4/0x364 kernel/locking/lockdep.c:5842
 __raw_spin_lock_irq include/linux/spinlock_api_smp.h:142 [inline]
 _raw_spin_lock_irq+0x58/0x70 kernel/locking/spinlock.c:174
 spin_lock_irq include/linux/spinlock.h:372 [inline]
 ep_open+0x70/0x2ec drivers/usb/gadget/legacy/inode.c:824
 do_dentry_open+0x5c4/0xfc0 fs/open.c:947
 vfs_open+0x44/0x2dc fs/open.c:1052
 do_open fs/namei.c:4700 [inline]
 path_openat+0x21fc/0x2a60 fs/namei.c:4863
 do_file_open+0x1c8/0x2e8 fs/namei.c:4892
 do_sys_openat2+0x114/0x1e8 fs/open.c:1368
 do_sys_open+0xb0/0xe0 fs/open.c:1374
 __do_sys_openat fs/open.c:1390 [inline]
 __se_sys_openat fs/open.c:1385 [inline]
 __arm64_sys_openat+0xa0/0xbc fs/open.c:1385
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
 el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
 el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594
Code: d503245f d343fc08 d2d00009 f2fbffe9 (38696908) 
---[ end trace 0000000000000000 ]---
----------------
Code disassembly (best guess):
   0:	d503245f 	bti	c
   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


Tested on:

commit:         365f9c7a Merge branches 'for-next/core' and 'for-next/..
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=174c8c9e580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=72c97575381cec47
dashboard link: https://syzkaller.appspot.com/bug?extid=df9e891bf8ea586f846b
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
userspace arch: arm64
patch:          https://syzkaller.appspot.com/x/patch.diff?x=1176caea580000