Re: [PATCH] mm/slab: reject unsupported kmalloc sizes

[Alan Stern]

On Mon, Aug 17, 2026 at 04:40:18PM -0400, Zi Yan wrote:
> kmalloc is used to allocate physically contiguous memory for kernel
> allocations. For requests larger than KMALLOC_MAX_CACHE_SIZE, kmalloc uses
> the page allocator and can only support up to KMALLOC_MAX_SIZE. For request
> sizes bigger than KMALLOC_MAX_SIZE, the page allocator can emit a WARN
> because kmalloc allocates an order greater than MAX_PAGE_ORDER. Systems
> with panic_on_warn=1 crash because of this WARN. Fix it by rejecting any
> kmalloc size bigger than KMALLOC_MAX_SIZE.
> 
> Fixes: aadb4bc4a1f9 ("SLUB: direct pass through of page size or higher kmalloc requests")
> Reported-by: syzbot+805630f1453e490427fa@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://lore.kernel.org/all/6a820ebc.9ebadd4d.20b15e.001b.GAE@xxxxxxxxxx/
> Tested-by: syzbot+805630f1453e490427fa@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> ---
> It fixes a page allocator warning (order > MAX_PAGE_ORDER) when gadgetfs
> requests excessively large memory from kmalloc. Instead of adding
> __GFP_NOWARN to suppress the warning, as was done for usbfs[1], change
> kmalloc to return NULL without a warning for this specific issue.
> 
> [1] commit 4f2629ea67e72 ("USB: usbfs: Don't WARN about excessively large memory allocations")

Thanks for doing this.  If you like, I can write a follow-up patch to 
remove the __GFP_NOWARN added in 4f2629ea67e72, now that it isn't needed 
any more.

Alan Stern