Re: [syzbot] [mm?] WARNING in v9fs_fid_get_acl (2)

[Dominique Martinet]

(+Nguyen in Cc as he tried resending sloppy patches after this)

Andrew Morton wrote on Sat, Sep 19, 2026 at 03:14:51AM -0700:
> > WARNING: mm/page_alloc.c:5340 at alloc_order_allowed mm/page_alloc.c:5340 [inline], CPU#0: syz.1.357/7872
> > WARNING: mm/page_alloc.c:5340 at __alloc_frozen_pages_noprof+0x2137/0x3300 mm/page_alloc.c:5397, CPU#0: syz.1.357/7872
> 
> Thanks.  Caused by an old v9fs bug.  A fix was proposed but never merged:
> https://lists.openwall.net/linux-kernel/2024/02/02/806?utm_source=chatgpt.com

Right, we've been going in circle with this since forever, and nobody
answered Christian Schoenebeck's question[1] about what the limit should
be, and while I don't care much ultimately I sort of agree with him
(e.g. limit should be XATTR_SIZE_MAX for anything that the VFS layer
touches, but acl are converted within the 9p subsystem and could be
arbitrarily large so status quo of a KMALLOC_MAX_SIZE limit because they
could come from something else)

Andrew, if you have an opinion on whether we should cap the acl sizes
anyway, please say...

[1] https://lore.kernel.org/all/Z1n-Ue19Pa_AWVu0@xxxxxxxxxxxxx/T/#md7c1e009696501b3b87940cb613150bdebd1db28


-- 
Dominique Martinet | Asmadeus