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t=1787736497; bh=VkPDzgtqpJZ+C+pFu3IpQfmXypArccQSfZj/VF6NMbQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=RkFXSijRbA6EM3ZrjDU8tSwuriXKTTOKjpopi5CErpNWTeCRYBX/qsSUpyn8Ggw/R kPodnkEfLkODpYExzkYsht60y+Ht4NVpAtwCjHkGW071tyXfWzKONDRORVx0+2QE2h zAUsNR84Y0VJkVKEYg+xwJ/PsQmf2mhC46R5H69eX6Rj0okfWJkL0JaWA24/a/ue6K 8S/3idW0QkFMKJ3nRlZj8zfw3V9bg3e/B1zBxkMQNBUagKF5Fq7fD2KGSvyp8gNOXB 7N8bQJJqeIvVJDE0sVvbKo0VkfJSliyfgJII+5KVQG+v9W2NAhWYpNB1mlsc33s3gV W90ZgP8IBSMLQ== Message-ID: <82f138f5-11d4-4839-94a3-c226fd982715@kernel.org> Date: Wed, 26 Aug 2026 11:28:12 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/slab: reject unsupported kmalloc sizes To: Zi Yan , Harry Yoo , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Alan Stern , Greg Kroah-Hartman Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, syzbot+805630f1453e490427fa@syzkaller.appspotmail.com, stable@vger.kernel.org References: <20260817-limit_kmalloc_size-v1-1-5bef487701cc@nvidia.com> From: "Vlastimil Babka (SUSE)" Content-Language: en-US Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 1805D1C0004 X-Stat-Signature: ba1zhpqz9tidohncb61opcffwxka7kb1 X-HE-Tag: 1787736497-435895 X-HE-Meta: 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 oVUjWIuH 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/17/26 22:40, 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@syzkaller.appspotmail.com > Closes: https://lore.kernel.org/all/6a820ebc.9ebadd4d.20b15e.001b.GAE@google.com/ > Tested-by: syzbot+805630f1453e490427fa@syzkaller.appspotmail.com > Signed-off-by: Zi Yan > Cc: stable@vger.kernel.org > --- > 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") So I checked and for kvmalloc() we have in __kvmalloc_node_noprof() /* Don't even allow crazy sizes */ if (unlikely(size > INT_MAX)) { WARN_ON_ONCE(!(flags & __GFP_NOWARN)); return NULL; } This comes from Linus in commit 7661809d493b4. I'd do the same thing here then. Thus there would be a useful warning for e.g. development mistakes resulting in the size to be unexpectedly high. Callers passing size that comes from userspace or similar untrusted source can either pass __GFP_NOWARN or sanitize the size to what they expect to be sane (which is context dependent and I assume actually way lower than kmalloc limits in practice). Note that passing even sizes within but close to/at the limit, trusting blindly some external source, can succeed the allocations but effectively DoS the system with heavy reclaim/compaction. So caller sanitization should still be preferred IMHO. Some of the recent arguments from Linus [1] would apply to this too, I think. [1] https://lore.kernel.org/all/CAHk-=wiSmgwwLKCqJwGS-dVHnSLU8W+7q1UQq-G9=TBGGZbuhQ@mail.gmail.com/ > --- > mm/slub.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/mm/slub.c b/mm/slub.c > index 0337e60db5ace..a3071f4ef1945 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -5263,7 +5263,12 @@ static void *___kmalloc_large_node(size_t size, gfp_t flags, int node) > { > struct page *page; > void *ptr = NULL; > - unsigned int order = get_order(size); > + unsigned int order; > + > + if (size > KMALLOC_MAX_SIZE) > + return NULL; > + > + order = get_order(size); > > if (unlikely(flags & GFP_SLAB_BUG_MASK)) > flags = kmalloc_fix_flags(flags); > > --- > base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f > change-id: 20260817-limit_kmalloc_size-3a4a2c73beac > > Best regards, > -- > Yan, Zi >