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Mon, 22 Sep 2025 22:11:50 -0700 (PDT) MIME-Version: 1.0 References: <20250922170357.148588-1-viswanathiyyappan@gmail.com> In-Reply-To: From: viswanath Date: Tue, 23 Sep 2025 10:41:39 +0530 X-Gm-Features: AS18NWAz93VsrUOfHCTB4kaK6hHURodNuYHUG5D8F71sybC2WG0KWMO2FAQjnLQ Message-ID: Subject: Re: [RFC PATCH] mm/slab: Add size validation in kmalloc_array_* functions To: Harry Yoo Cc: vbabka@suse.cz, akpm@linux-foundation.org, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, skhan@linuxfoundation.org, david.hunter.linux@gmail.com, linux-kernel-mentees@lists.linux.dev, syzbot+94d20db923b9f51be0df@syzkaller.appspotmail.com Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 6F095140002 X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: 4m7espyw1gxhqweqxm6spp5ybkm3q3g1 X-HE-Tag: 1758604312-226811 X-HE-Meta: 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 naZMx6W1 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 22 Sept 2025 at 23:30, Harry Yoo wrote: > When bytes > KKMALLOC_MAX_SIZE (8K on my system), kmalloc redirects allocation > to the buddy allocator, which can allocate up to (PAGE_SIZE << MAX_PAGE_ORDER) > bytes (4M on my system). In include/linux/slab.h, KMALLOC_MAX_SIZE is ultimately defined as PAGE_SIZE << MAX_PAGE_ORDER and KMALLOC_MAX_CACHE_SIZE as PAGE_SIZE << 1 I was using those definitions > Because allocating a page with order > MAX_PAGE_ORDER page is never > supposed to succeed, the caller of kmalloc should be fixed rather than > kmalloc itself. So, Is it almost never a good idea to add new validation in the allocator code? > I think the right fix should be to return -EINVAL in max_vclocks_store() > if max * sizeof(int) exceeds PAGE_SIZE << MAX_PAGE_ORDER? Thanks, I will go ahead with this approach Thanks, Viswanath