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KASAN: null-ptr-deref Write in f2fs_issue_flush

Status: upstream: reported C repro on 2025/10/01 01:02
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+1f2ac055dbc0980c23b3@syzkaller.appspotmail.com
First crash: 2d07h, last: 1d05h
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2025/10/02 linux-6.1.y (ToT) 7b34dc04e4ff C [report] KASAN: null-ptr-deref Write in f2fs_issue_flush
2025/10/02 upstream (ToT) d2b2fea3503e C Didn't crash
▶ ▼ Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-5-15 KASAN: null-ptr-deref Write in f2fs_issue_flush 12 C 4 2d13h 2d13h 0/2 upstream: reported C repro on 2025/09/30 19:35

Sample crash report:
         option from the mount to silence this warning.
=======================================================
F2FS-fs (loop0): Try to recover all the superblocks, ret: 0
==================================================================
BUG: KASAN: null-ptr-deref in f2fs_issue_flush+0x11c/0x8b8 fs/f2fs/segment.c:-1
Write of size 4 at addr 000000000000005c by task syz.0.17/4488

CPU: 1 PID: 4488 Comm: syz.0.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/30/2025
Call trace:
 dump_backtrace+0x1c8/0x1f4 arch/arm64/kernel/stacktrace.c:158
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:165
 __dump_stack+0x30/0x40 lib/dump_stack.c:88
 dump_stack_lvl+0xf8/0x160 lib/dump_stack.c:106
 print_report+0x40/0x68 mm/kasan/report.c:423
 kasan_report+0xa8/0x100 mm/kasan/report.c:524
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x260/0x2a0 mm/kasan/generic.c:189
 __kasan_check_write+0x2c/0x3c mm/kasan/shadow.c:37
 f2fs_issue_flush+0x11c/0x8b8 fs/f2fs/segment.c:-1
 f2fs_do_sync_file+0xe20/0x1740 fs/f2fs/file.c:380
 f2fs_ioc_commit_atomic_write fs/f2fs/file.c:2253 [inline]
 __f2fs_ioctl+0x33c0/0xaab8 fs/f2fs/file.c:4315
 f2fs_ioctl+0x130/0x1a0 fs/f2fs/file.c:4403
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:856
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
 do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
 el0_svc+0x58/0x138 arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585
==================================================================
Unable to handle kernel NULL pointer dereference at virtual address 000000000000005c
Mem abort info:
  ESR = 0x0000000096000006
  EC = 0x25: DABT (current EL), IL = 32 bits
  SET = 0, FnV = 0
  EA = 0, S1PTW = 0
  FSC = 0x06: level 2 translation fault
Data abort info:
  ISV = 0, ISS = 0x00000006
  CM = 0, WnR = 0
user pgtable: 4k pages, 48-bit VAs, pgdp=000000012eb58000
[000000000000005c] pgd=080000011d353003, p4d=080000011d353003, pud=0800000115058003, pmd=0000000000000000
Internal error: Oops: 0000000096000006 [#1] PREEMPT SMP
Modules linked in:
CPU: 0 PID: 4488 Comm: syz.0.17 Tainted: G    B              syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/30/2025
pstate: 82400005 (Nzcv daif +PAN -UAO +TCO -DIT -SSBS BTYPE=--)
pc : __lse_atomic_add arch/arm64/include/asm/atomic_lse.h:27 [inline]
pc : arch_atomic_add arch/arm64/include/asm/atomic.h:28 [inline]
pc : arch_atomic_inc include/linux/atomic/atomic-arch-fallback.h:424 [inline]
pc : atomic_inc include/linux/atomic/atomic-instrumented.h:191 [inline]
pc : f2fs_issue_flush+0x12c/0x8b8 fs/f2fs/segment.c:578
lr : __lse_atomic_add arch/arm64/include/asm/atomic_lse.h:27 [inline]
lr : arch_atomic_add arch/arm64/include/asm/atomic.h:28 [inline]
lr : arch_atomic_inc include/linux/atomic/atomic-arch-fallback.h:424 [inline]
lr : atomic_inc include/linux/atomic/atomic-instrumented.h:191 [inline]
lr : f2fs_issue_flush+0x128/0x8b8 fs/f2fs/segment.c:578
sp : ffff8000211e74c0
x29: ffff8000211e75c0 x28: ffff0000d895cf94 x27: dfff800000000000
x26: ffff70000423ce9c x25: 0000000000000000 x24: 00000000000001c5
x23: ffff8000211e7500 x22: 000000000000000a x21: ffff0000d895c000
x20: 000000000000005c x19: 00000000180022de x18: ffff800011abbcc0
x17: 0000000000000000 x16: ffff800008042c8c x15: 0000000000000000
x14: 00000000ffffffff x13: 0000000000000001 x12: 0000000000ff0100
x11: ff0080000a302114 x10: 0000000000000000 x9 : ffff80000a302114
x8 : 0000000000000001 x7 : 0000000000000001 x6 : 0000000000000001
x5 : ffff8000211e6e98 x4 : ffff8000151a4820 x3 : ffff800008191794
x2 : 0000000000000001 x1 : 0000000000000000 x0 : 0000000000000000
Call trace:
 __lse_atomic_add arch/arm64/include/asm/atomic_lse.h:-1 [inline]
 arch_atomic_add arch/arm64/include/asm/atomic.h:28 [inline]
 arch_atomic_inc include/linux/atomic/atomic-arch-fallback.h:424 [inline]
 atomic_inc include/linux/atomic/atomic-instrumented.h:191 [inline]
 f2fs_issue_flush+0x12c/0x8b8 fs/f2fs/segment.c:578
 f2fs_do_sync_file+0xe20/0x1740 fs/f2fs/file.c:380
 f2fs_ioc_commit_atomic_write fs/f2fs/file.c:2253 [inline]
 __f2fs_ioctl+0x33c0/0xaab8 fs/f2fs/file.c:4315
 f2fs_ioctl+0x130/0x1a0 fs/f2fs/file.c:4403
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:856
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x2bc arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
 do_el0_svc+0x58/0x13c arch/arm64/kernel/syscall.c:204
 el0_svc+0x58/0x138 arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585
Code: 375008b3 d503201f 97867de2 52800028 (b828029f) 
---[ end trace 0000000000000000 ]---
----------------
Code disassembly (best guess):
   0:	375008b3 	tbnz	w19, #10, 0x114
   4:	d503201f 	nop
   8:	97867de2 	bl	0xfffffffffe19f790
   c:	52800028 	mov	w8, #0x1                   	// #1
* 10:	b828029f 	stadd	w8, [x20] <-- trapping instruction

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/10/01 05:35 linux-6.1.y 7b34dc04e4ff 65a0eece .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-linux-6-1-kasan-arm64 KASAN: null-ptr-deref Write in f2fs_issue_flush
2025/10/01 01:02 linux-6.1.y 7b34dc04e4ff 65a0eece .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 KASAN: null-ptr-deref Write in f2fs_issue_flush
2025/10/01 01:01 linux-6.1.y 7b34dc04e4ff 65a0eece .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 KASAN: null-ptr-deref Write in f2fs_issue_flush
* Struck through repros no longer work on HEAD.