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

[David Laight <david.laight.linux@gmail.com>]

On Fri, 21 Aug 2026 10:24:36 -0400
"Zi Yan" <ziy@nvidia.com> wrote:

> On Fri Aug 21, 2026 at 4:30 AM EDT, David Laight wrote:
> > On Sun, 16 Aug 2026 13:52:01 -0700
> > Andrew Morton <akpm@linux-foundation.org> wrote:
> >  
> >> On Sun, 16 Aug 2026 12:25:48 -0700 syzbot <syzbot+805630f1453e490427fa@syzkaller.appspotmail.com> wrote:
> >>   
> >> > Hello,
> >> > 
> >> > syzbot found the following issue on:
> >> > 
> >> > HEAD commit:    3d6d817622b0 Merge tag 'scsi-fixes' of git://git.kernel.or..
> >> > git tree:       upstream
> >> > console output: https://syzkaller.appspot.com/x/log.txt?x=15927479580000
> >> > kernel config:  https://syzkaller.appspot.com/x/.config?x=a59830cba91a1981
> >> > dashboard link: https://syzkaller.appspot.com/bug?extid=805630f1453e490427fa
> >> > compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
> >> > 
> >> > Unfortunately, I don't have any reproducer for this issue yet.
> >> > 
> >> > Downloadable assets:
> >> > disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-3d6d8176.raw.xz
> >> > vmlinux: https://storage.googleapis.com/syzbot-assets/d19e0514c02a/vmlinux-3d6d8176.xz
> >> > kernel image: https://storage.googleapis.com/syzbot-assets/f6da706811f4/bzImage-3d6d8176.xz
> >> > 
> >> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> >> > Reported-by: syzbot+805630f1453e490427fa@syzkaller.appspotmail.com
> >> > 
> >> > gadgetfs: bound to dummy_udc driver
> >> > ------------[ cut here ]------------
> >> > 1
> >> > WARNING: mm/page_alloc.c:5280 at __alloc_frozen_pages_noprof+0x2ce/0x380 mm/page_alloc.c:5280, CPU#0: syz.0.0/5319    
> >> 
> >> Thanks.  drivers/usb/gadget is the offender.
> >> 
> >> Gemini sums it up well.  "ep_write_iter() needs a bounds check prior to
> >> memory allocation".  https://share.gemini.google/5NzjyttO0ULc
> >> 
> >> I expect an easy fix would be
> >> 
> >> --- a/drivers/usb/gadget/legacy/inode.c~a
> >> +++ a/drivers/usb/gadget/legacy/inode.c
> >> @@ -666,7 +666,7 @@ ep_write_iter(struct kiocb *iocb, struct
> >>  		return -EBADMSG;
> >>  	}
> >>  
> >> -	buf = kmalloc(len, GFP_KERNEL);
> >> +	buf = kmalloc(len, GFP_KERNEL|__GFP_NOWARN);
> >>  	if (unlikely(!buf)) {
> >>  		mutex_unlock(&epdata->lock);
> >>  		return -ENOMEM;
> >> 
> >> or do what Gemini said.  Me, I'll add some cc's and run away.  
> >
> > Should there be a separate flags for 'request too large' and
> > 'no memory available' ?  
> 
> What flags? Are you suggesting kmalloc should return an ERR_PTR to
> distinguish different error types?

That would break to much...
I was thinking of a GFP_NOWARN_TOOBIG.

That isn't enough to change the errno though.
But a smaller sanity limit may make sense anyway.

David

> 
> >
> > Although the errno for 'len too big' should probably be EINVAL
> > not ENOMEM.
> >
> > David
> >  
> >> 
> >>   
> >> > Modules linked in:
> >> > CPU: 0 UID: 0 PID: 5319 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full) 
> >> > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
> >> > RIP: 0010:__alloc_frozen_pages_noprof+0x2ce/0x380 mm/page_alloc.c:5280
> >> > Code: 74 10 4c 89 e7 89 54 24 0c e8 0e 2c 0e 00 8b 54 24 0c 49 83 3c 24 00 0f 85 ab fe ff ff e9 ac fe ff ff c6 05 95 d2 18 0e 01 90 <0f> 0b 90 e9 17 ff ff ff a9 00 00 08 00 48 8b 4c 24 10 4c 8d 44 24
> >> > RSP: 0018:ffffc9000e13fa20 EFLAGS: 00010246
> >> > RAX: ffffc9000e13fa00 RBX: 0000000000000013 RCX: 0000000000000000
> >> > RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffc9000e13fa88
> >> > RBP: ffffc9000e13fb08 R08: ffffc9000e13fa87 R09: 0000000000000000
> >> > R10: ffffc9000e13fa60 R11: fffff52001c27f51 R12: 0000000000000000
> >> > R13: 1ffff92001c27f48 R14: 0000000000040cc0 R15: dffffc0000000000
> >> > FS:  00007f6f4a58c6c0(0000) GS:ffff88808c549000(0000) knlGS:0000000000000000
> >> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> > CR2: 00002000000010a0 CR3: 000000004323d000 CR4: 0000000000352ef0
> >> > Call Trace:
> >> >  <TASK>
> >> >  alloc_pages_mpol+0x212/0x380 mm/mempolicy.c:2490
> >> >  ___kmalloc_large_node+0x4c/0x120 mm/slub.c:5274
> >> >  __kmalloc_large_node_noprof+0x18/0x90 mm/slub.c:5305
> >> >  __do_kmalloc_node mm/slub.c:5322 [inline]
> >> >  __kmalloc_noprof+0x405/0x720 mm/slub.c:5359
> >> >  _kmalloc_noprof include/linux/slab.h:992 [inline]
> >> >  ep_write_iter+0x1bc/0x500 drivers/usb/gadget/legacy/inode.c:669
> >> >  new_sync_write fs/read_write.c:595 [inline]
> >> >  vfs_write+0x612/0xba0 fs/read_write.c:687
> >> >  ksys_write+0x150/0x270 fs/read_write.c:739
> >> >  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> >> >  do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
> >> >  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >> > RIP: 0033:0x7f6f4979e0d9
> >> > 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:00007f6f4a58bfe8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
> >> > RAX: ffffffffffffffda RBX: 00007f6f49a25fa0 RCX: 00007f6f4979e0d9
> >> > RDX: 00000000ffffffb9 RSI: 0000000000000000 RDI: 0000000000000004
> >> > RBP: 00007f6f49835024 R08: 0000000000000000 R09: 0000000000000000
> >> > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> >> > R13: 00007f6f49a26038 R14: 00007f6f49a25fa0 R15: 00007ffc6cf49328
> >> >  </TASK>
> >> >     
> >> 
> >>   
> 
> 
> 
>