[syzbot] [mm?] WARNING in folio_add_new_anon_rmap

[syzbot] [mm?] WARNING in folio_add_new_anon_rmap

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    f90aadf1c67c Add linux-next specific files for 20260311
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=12309806580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=2b10825359140979
dashboard link: https://syzkaller.appspot.com/bug?extid=e24a2e34fad0efbac047
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=10cb575a580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14db4d52580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/aca9c54a7de2/disk-f90aadf1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/736fd5e68863/vmlinux-f90aadf1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/eb13b7d81d1b/bzImage-f90aadf1.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e24a2e34fad0efbac047@syzkaller.appspotmail.com

------------[ cut here ]------------
address < vma->vm_start || address + (nr << 12) > vma->vm_end
WARNING: mm/rmap.c:1682 at folio_add_new_anon_rmap+0x5fe/0x14b0 mm/rmap.c:1681, CPU#1: syz.2.19/6118
Modules linked in:
CPU: 1 UID: 0 PID: 6118 Comm: syz.2.19 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/27/2026
RIP: 0010:folio_add_new_anon_rmap+0x5fe/0x14b0 mm/rmap.c:1681
Code: 89 f5 4d 8b 36 4c 89 e7 4c 89 f6 e8 ec aa a9 ff 4d 39 f4 73 1a e8 82 a8 a9 ff 4c 8b 74 24 10 49 bc 00 00 00 00 00 fc ff df 90 <0f> 0b 90 eb 5a 44 89 f8 c1 e0 0c 48 98 49 01 c4 49 83 c5 08 4c 89
RSP: 0018:ffffc900036675a0 EFLAGS: 00010293
RAX: ffffffff821d041e RBX: ffffea0001c0c1c0 RCX: ffff888060bf5b80
RDX: 0000000000000000 RSI: 00002000004ca000 RDI: 00002000004cb000
RBP: 0000000000000000 R08: ffffea0001c0c1c7 R09: 1ffffd4000381838
R10: dffffc0000000000 R11: fffff94000381839 R12: dffffc0000000000
R13: ffff8880784ad788 R14: ffffea0001c0c1c8 R15: 0000000000000001
FS:  00007f9a968ce6c0(0000) GS:ffff88812553e000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00002000002b8000 CR3: 000000007c646000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 mfill_atomic_install_pte+0x578/0x870 mm/userfaultfd.c:390
 __mfill_atomic_pte+0x3c4/0x5f0 mm/userfaultfd.c:523
 mfill_atomic_pte_copy mm/userfaultfd.c:557 [inline]
 mfill_atomic_pte mm/userfaultfd.c:865 [inline]
 mfill_atomic mm/userfaultfd.c:923 [inline]
 mfill_atomic_copy+0x4d9/0x1330 mm/userfaultfd.c:950
 userfaultfd_copy fs/userfaultfd.c:1642 [inline]
 userfaultfd_ioctl+0x2b8a/0x4b00 fs/userfaultfd.c:2059
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 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: 0033:0x7f9a9599c799
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:00007f9a968ce028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f9a95c15fa0 RCX: 00007f9a9599c799
RDX: 0000200000000040 RSI: 00000000c028aa03 RDI: 0000000000000003
RBP: 00007f9a95a32c99 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9a95c16038 R14: 00007f9a95c15fa0 R15: 00007ffd373c5448
 </TASK>


---
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Re: [syzbot] [mm?] WARNING in folio_add_new_anon_rmap

[Harry Yoo]

#syz test

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 510c6dcb9824..73adf9ffcac2 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -880,7 +880,7 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx,
 		.dst_start = dst_start,
 		.src_start = src_start,
 		.flags = flags,
-
+		.len = len,
 		.src_addr = src_start,
 		.dst_addr = dst_start,
 	};

Re: [syzbot] [mm?] WARNING in folio_add_new_anon_rmap

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+e24a2e34fad0efbac047@syzkaller.appspotmail.com
Tested-by: syzbot+e24a2e34fad0efbac047@syzkaller.appspotmail.com

Tested on:

commit:         b84a0ebe Add linux-next specific files for 20260313
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=11f43406580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d079c776411aaf59
dashboard link: https://syzkaller.appspot.com/bug?extid=e24a2e34fad0efbac047
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=16cfdd52580000

Note: testing is done by a robot and is best-effort only.

Re: [syzbot] [mm?] WARNING in folio_add_new_anon_rmap

[Mike Rapoport]

Hi Harry,

Thanks for the fix :)

@Andrew, can you please fold it into
"userfaultfd: introduce struct mfill_state"

On Mon, Mar 16, 2026 at 03:19:49PM +0900, Harry Yoo wrote:
> #syz test
> 
> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
> index 510c6dcb9824..73adf9ffcac2 100644
> --- a/mm/userfaultfd.c
> +++ b/mm/userfaultfd.c
> @@ -880,7 +880,7 @@ static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx,
>  		.dst_start = dst_start,
>  		.src_start = src_start,
>  		.flags = flags,
> -
> +		.len = len,
>  		.src_addr = src_start,
>  		.dst_addr = dst_start,
>  	};
> 

-- 
Sincerely yours,
Mike.