* [syzbot] [fuse?] KASAN: use-after-free Write in fuse_copy_do
@ 2026-03-03 22:24 syzbot
2026-03-03 22:36 ` Joanne Koong
0 siblings, 1 reply; 3+ messages in thread
From: syzbot @ 2026-03-03 22:24 UTC (permalink / raw)
To: linux-fsdevel, linux-kernel, miklos, syzkaller-bugs
Hello,
syzbot found the following issue on:
HEAD commit: c025f6cf4209 Add linux-next specific files for 20260303
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=135770ba580000
kernel config: https://syzkaller.appspot.com/x/.config?x=54b410fabe2a4318
dashboard link: https://syzkaller.appspot.com/bug?extid=23299dfcac137a96834a
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1671b006580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1166bb5a580000
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/e2497bde352d/disk-c025f6cf.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/36827cb45429/vmlinux-c025f6cf.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7ebf1ed6bb73/bzImage-c025f6cf.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+23299dfcac137a96834a@syzkaller.appspotmail.com
==================================================================
BUG: KASAN: use-after-free in fuse_copy_do+0x193/0x380 fs/fuse/dev.c:-1
Write of size 2 at addr ffff888070528fff by task syz.0.17/6005
CPU: 0 UID: 0 PID: 6005 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xba/0x230 mm/kasan/report.c:482
kasan_report+0x117/0x150 mm/kasan/report.c:595
check_region_inline mm/kasan/generic.c:-1 [inline]
kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
__asan_memcpy+0x40/0x70 mm/kasan/shadow.c:106
fuse_copy_do+0x193/0x380 fs/fuse/dev.c:-1
fuse_copy_folio+0xefc/0x1b00 fs/fuse/dev.c:1166
fuse_notify_store fs/fuse/dev.c:1821 [inline]
fuse_notify fs/fuse/dev.c:2109 [inline]
fuse_dev_do_write+0x2b9d/0x4060 fs/fuse/dev.c:2205
fuse_dev_write+0x177/0x220 fs/fuse/dev.c:2289
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x61d/0xb90 fs/read_write.c:688
ksys_write+0x150/0x270 fs/read_write.c:740
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe8c659c799
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fe8c7476028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fe8c6815fa0 RCX: 00007fe8c659c799
RDX: 000000000000002a RSI: 0000200000000080 RDI: 0000000000000003
RBP: 00007fe8c6632bd9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe8c6816038 R14: 00007fe8c6815fa0 R15: 00007ffd95eaba38
</TASK>
The buggy address belongs to the physical page:
page: refcount:3 mapcount:0 mapping:ffff88805c1c4f20 index:0x7 pfn:0x70528
memcg:ffff88802ce3a880
aops:empty_aops ino:1 dentry name(?):"/"
flags: 0xfff00000000005(locked|referenced|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000005 0000000000000000 dead000000000122 ffff88805c1c4f20
raw: 0000000000000007 0000000000000000 00000003ffffffff ffff88802ce3a880
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Movable, gfp_mask 0x140cca(GFP_HIGHUSER_MOVABLE|__GFP_COMP), pid 6005, tgid 6004 (syz.0.17), ts 103948279019, free_ts 103868818778
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x231/0x280 mm/page_alloc.c:1892
prep_new_page mm/page_alloc.c:1900 [inline]
get_page_from_freelist+0x23a1/0x2440 mm/page_alloc.c:3965
__alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5253
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2484
alloc_frozen_pages_noprof mm/mempolicy.c:2555 [inline]
alloc_pages_noprof+0xa8/0x190 mm/mempolicy.c:2575
folio_alloc_noprof+0x1e/0x30 mm/mempolicy.c:2585
filemap_alloc_folio_noprof+0x111/0x470 mm/filemap.c:1013
__filemap_get_folio_mpol+0x3fc/0xb00 mm/filemap.c:2011
__filemap_get_folio include/linux/pagemap.h:774 [inline]
filemap_grab_folio include/linux/pagemap.h:854 [inline]
fuse_notify_store fs/fuse/dev.c:1813 [inline]
fuse_notify fs/fuse/dev.c:2109 [inline]
fuse_dev_do_write+0x298b/0x4060 fs/fuse/dev.c:2205
fuse_dev_write+0x177/0x220 fs/fuse/dev.c:2289
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x61d/0xb90 fs/read_write.c:688
ksys_write+0x150/0x270 fs/read_write.c:740
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 6002 tgid 6002 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
__free_pages_prepare mm/page_alloc.c:1436 [inline]
free_unref_folios+0xd71/0x1530 mm/page_alloc.c:3043
folios_put_refs+0x9ff/0xb40 mm/swap.c:1008
free_pages_and_swap_cache+0x2e7/0x5b0 mm/swap_state.c:401
__tlb_batch_free_encoded_pages mm/mmu_gather.c:138 [inline]
tlb_batch_pages_flush mm/mmu_gather.c:151 [inline]
tlb_flush_mmu_free mm/mmu_gather.c:417 [inline]
tlb_flush_mmu+0x6d3/0xa30 mm/mmu_gather.c:424
tlb_finish_mmu+0xf9/0x230 mm/mmu_gather.c:549
exit_mmap+0x498/0xa10 mm/mmap.c:1315
__mmput+0x118/0x430 kernel/fork.c:1179
exit_mm+0x18e/0x250 kernel/exit.c:581
do_exit+0x8b9/0x2580 kernel/exit.c:962
do_group_exit+0x21b/0x2d0 kernel/exit.c:1116
__do_sys_exit_group kernel/exit.c:1127 [inline]
__se_sys_exit_group kernel/exit.c:1125 [inline]
__x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1125
x64_sys_call+0x221a/0x2240 arch/x86/include/generated/asm/syscalls_64.h:232
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Memory state around the buggy address:
ffff888070528f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff888070528f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff888070529000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
^
ffff888070529080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff888070529100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.
syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.
If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)
If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report
If you want to undo deduplication, reply with:
#syz undup
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [syzbot] [fuse?] KASAN: use-after-free Write in fuse_copy_do
2026-03-03 22:24 [syzbot] [fuse?] KASAN: use-after-free Write in fuse_copy_do syzbot
@ 2026-03-03 22:36 ` Joanne Koong
2026-03-03 22:38 ` syzbot
0 siblings, 1 reply; 3+ messages in thread
From: Joanne Koong @ 2026-03-03 22:36 UTC (permalink / raw)
To: syzbot; +Cc: linux-fsdevel, linux-kernel, miklos, syzkaller-bugs
On Tue, Mar 3, 2026 at 2:24 PM syzbot
<syzbot+23299dfcac137a96834a@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: c025f6cf4209 Add linux-next specific files for 20260303
> git tree: linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=135770ba580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=54b410fabe2a4318
> dashboard link: https://syzkaller.appspot.com/bug?extid=23299dfcac137a96834a
> compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1671b006580000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1166bb5a580000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/e2497bde352d/disk-c025f6cf.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/36827cb45429/vmlinux-c025f6cf.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/7ebf1ed6bb73/bzImage-c025f6cf.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+23299dfcac137a96834a@syzkaller.appspotmail.com
>
> ==================================================================
> BUG: KASAN: use-after-free in fuse_copy_do+0x193/0x380 fs/fuse/dev.c:-1
> Write of size 2 at addr ffff888070528fff by task syz.0.17/6005
>
> CPU: 0 UID: 0 PID: 6005 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
> Call Trace:
> <TASK>
> dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
> print_address_description mm/kasan/report.c:378 [inline]
> print_report+0xba/0x230 mm/kasan/report.c:482
> kasan_report+0x117/0x150 mm/kasan/report.c:595
> check_region_inline mm/kasan/generic.c:-1 [inline]
> kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
> __asan_memcpy+0x40/0x70 mm/kasan/shadow.c:106
> fuse_copy_do+0x193/0x380 fs/fuse/dev.c:-1
> fuse_copy_folio+0xefc/0x1b00 fs/fuse/dev.c:1166
> fuse_notify_store fs/fuse/dev.c:1821 [inline]
I think this is a fallout from the misordered lines detected in
https://lore.kernel.org/all/202603031522.e4lroM3J-lkp@intel.com/T/#u
> fuse_notify fs/fuse/dev.c:2109 [inline]
> fuse_dev_do_write+0x2b9d/0x4060 fs/fuse/dev.c:2205
> fuse_dev_write+0x177/0x220 fs/fuse/dev.c:2289
> new_sync_write fs/read_write.c:595 [inline]
> vfs_write+0x61d/0xb90 fs/read_write.c:688
> ksys_write+0x150/0x270 fs/read_write.c:740
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7fe8c659c799
> Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fe8c7476028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> RAX: ffffffffffffffda RBX: 00007fe8c6815fa0 RCX: 00007fe8c659c799
> RDX: 000000000000002a RSI: 0000200000000080 RDI: 0000000000000003
> RBP: 00007fe8c6632bd9 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007fe8c6816038 R14: 00007fe8c6815fa0 R15: 00007ffd95eaba38
> </TASK>
>
> The buggy address belongs to the physical page:
> page: refcount:3 mapcount:0 mapping:ffff88805c1c4f20 index:0x7 pfn:0x70528
> memcg:ffff88802ce3a880
> aops:empty_aops ino:1 dentry name(?):"/"
> flags: 0xfff00000000005(locked|referenced|node=0|zone=1|lastcpupid=0x7ff)
> raw: 00fff00000000005 0000000000000000 dead000000000122 ffff88805c1c4f20
> raw: 0000000000000007 0000000000000000 00000003ffffffff ffff88802ce3a880
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 0, migratetype Movable, gfp_mask 0x140cca(GFP_HIGHUSER_MOVABLE|__GFP_COMP), pid 6005, tgid 6004 (syz.0.17), ts 103948279019, free_ts 103868818778
> set_page_owner include/linux/page_owner.h:32 [inline]
> post_alloc_hook+0x231/0x280 mm/page_alloc.c:1892
> prep_new_page mm/page_alloc.c:1900 [inline]
> get_page_from_freelist+0x23a1/0x2440 mm/page_alloc.c:3965
> __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5253
> alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2484
> alloc_frozen_pages_noprof mm/mempolicy.c:2555 [inline]
> alloc_pages_noprof+0xa8/0x190 mm/mempolicy.c:2575
> folio_alloc_noprof+0x1e/0x30 mm/mempolicy.c:2585
> filemap_alloc_folio_noprof+0x111/0x470 mm/filemap.c:1013
> __filemap_get_folio_mpol+0x3fc/0xb00 mm/filemap.c:2011
> __filemap_get_folio include/linux/pagemap.h:774 [inline]
> filemap_grab_folio include/linux/pagemap.h:854 [inline]
> fuse_notify_store fs/fuse/dev.c:1813 [inline]
> fuse_notify fs/fuse/dev.c:2109 [inline]
> fuse_dev_do_write+0x298b/0x4060 fs/fuse/dev.c:2205
> fuse_dev_write+0x177/0x220 fs/fuse/dev.c:2289
> new_sync_write fs/read_write.c:595 [inline]
> vfs_write+0x61d/0xb90 fs/read_write.c:688
> ksys_write+0x150/0x270 fs/read_write.c:740
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
> page last free pid 6002 tgid 6002 stack trace:
> reset_page_owner include/linux/page_owner.h:25 [inline]
> __free_pages_prepare mm/page_alloc.c:1436 [inline]
> free_unref_folios+0xd71/0x1530 mm/page_alloc.c:3043
> folios_put_refs+0x9ff/0xb40 mm/swap.c:1008
> free_pages_and_swap_cache+0x2e7/0x5b0 mm/swap_state.c:401
> __tlb_batch_free_encoded_pages mm/mmu_gather.c:138 [inline]
> tlb_batch_pages_flush mm/mmu_gather.c:151 [inline]
> tlb_flush_mmu_free mm/mmu_gather.c:417 [inline]
> tlb_flush_mmu+0x6d3/0xa30 mm/mmu_gather.c:424
> tlb_finish_mmu+0xf9/0x230 mm/mmu_gather.c:549
> exit_mmap+0x498/0xa10 mm/mmap.c:1315
> __mmput+0x118/0x430 kernel/fork.c:1179
> exit_mm+0x18e/0x250 kernel/exit.c:581
> do_exit+0x8b9/0x2580 kernel/exit.c:962
> do_group_exit+0x21b/0x2d0 kernel/exit.c:1116
> __do_sys_exit_group kernel/exit.c:1127 [inline]
> __se_sys_exit_group kernel/exit.c:1125 [inline]
> __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1125
> x64_sys_call+0x221a/0x2240 arch/x86/include/generated/asm/syscalls_64.h:232
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> Memory state around the buggy address:
> ffff888070528f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffff888070528f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >ffff888070529000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ^
> ffff888070529080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ffff888070529100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ==================================================================
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
>
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.
#syz test
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index da2e0f348890..2c16b94357d5 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1815,8 +1815,8 @@ static int fuse_notify_store(struct fuse_conn
*fc, unsigned int size,
if (IS_ERR(folio))
goto out_iput;
- nr_bytes = min(num, folio_size(folio) - folio_offset);
folio_offset = offset_in_folio(folio, pos);
+ nr_bytes = min(num, folio_size(folio) - folio_offset);
err = fuse_copy_folio(cs, &folio, folio_offset, nr_bytes, 0);
if (!folio_test_uptodate(folio) && !err && folio_offset == 0 &&
>
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
>
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
>
> If you want to undo deduplication, reply with:
> #syz undup
>
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [syzbot] [fuse?] KASAN: use-after-free Write in fuse_copy_do
2026-03-03 22:36 ` Joanne Koong
@ 2026-03-03 22:38 ` syzbot
0 siblings, 0 replies; 3+ messages in thread
From: syzbot @ 2026-03-03 22:38 UTC (permalink / raw)
To: joannelkoong, linux-fsdevel, linux-kernel, miklos, syzkaller-bugs
Hello,
syzbot tried to test the proposed patch but the build/boot failed:
failed to apply patch:
checking file fs/fuse/dev.c
patch: **** unexpected end of file in patch
Tested on:
commit: c025f6cf Add linux-next specific files for 20260303
git tree: linux-next
kernel config: https://syzkaller.appspot.com/x/.config?x=54b410fabe2a4318
dashboard link: https://syzkaller.appspot.com/bug?extid=23299dfcac137a96834a
compiler:
patch: https://syzkaller.appspot.com/x/patch.diff?x=1620f0ba580000
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2026-03-03 22:38 UTC | newest]
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2026-03-03 22:24 [syzbot] [fuse?] KASAN: use-after-free Write in fuse_copy_do syzbot
2026-03-03 22:36 ` Joanne Koong
2026-03-03 22:38 ` syzbot
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