From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 27CFC2F12CE; Thu, 16 Jul 2026 14:16:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784211374; cv=none; b=AP9roRdAYvxfhH6iRYjAKAHX2xVDSKML9AVX6TY221SM87y+Dt4p+B0TPM+o8iG7YGJNE6Ho+jWQC7hCQRtZrye7GZ8NT4OUEClvbnBZ99oC249inUk48H9TS7aiWj6sIzaJ47cMx3YS2h5kOezycKwph0d14UvOdmEEnc0fW8M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784211374; c=relaxed/simple; bh=cNcuEv+ep03CI5pWWfOG/ugTfVi3val6dkoquAO8Fl0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=qBDO3ah9uosbZLw0ozx29WU5juTOGUB5FfjQi1AbPhWiwBhI3lTWl9Y3pAk7sGxmbg2LY7JH+kXiKieXHfuIWaC4doYZa586QSrdKRSyUsY/PJjrhuA1DJ05yMY0EFq0AOM8HhfQRiJO8ykrXMES99lPXX7HvDPrKdYyzj8j1eA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=wDbiRdOT; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="wDbiRdOT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 181821F000E9; Thu, 16 Jul 2026 14:16:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1784211372; bh=hy6gQbKJtlVzMzRgke9tGnhpCkZNmwKgFguiLbQiK3U=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=wDbiRdOTzidecvWURLQ6KuqydemmnFmHHaKGr0VnKwEmTLWSbVS4SfdrbtmlsQCNt OTPbnSf8waEAMRnPQEUOOaFehPZ1YSPS16a+Pa12wZhMs9X8YtexfTKd+2obKOBAPT DYCUlWrbdnp2Gcx/igY0WOyFdXYlxIoZh+Dw7w3A= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Ketan Kishore , David Hildenbrand , Matthew Wilcox , Zi Yan , "David Hildenbrand (Arm)" , Brendan Jackman , Johannes Weiner , "Liam R. Howlett" , Lorenzo Stoakes , Luiz Capitulino , Michal Hocko , Mike Rapoport , Suren Baghdasaryan , Vlastimil Babka , Andrew Morton Subject: [PATCH 6.18 402/480] mm: page_ext: add count limit to page_ext_iter_next to prevent invalid PFN access Date: Thu, 16 Jul 2026 15:32:29 +0200 Message-ID: <20260716133053.505664037@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260716133044.672218725@linuxfoundation.org> References: <20260716133044.672218725@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ketan commit ffd017237cfe99e6e5602ab14179b0e6878a0840 upstream. The page_ext iteration API does not validate if the PFN still belongs to a valid section while advancing the iterator. When dynamically adding memory in the hotplug path, it can lead to a NULL pointer dereference during page_ext_lookup at the boundary of the last valid section when iterator count equals __pgcount. The for_each_page_ext() macro calls page_ext_iter_next() as its loop increment. for_each_page_ext() does a "__page_ext = page_ext_iter_next(&__iter)" at the end. This causes page_ext_iter_next() to increment iter->index past __pgcount and call page_ext_lookup(start_pfn + __pgcount). During memory hotplug (online), the PFN at start_pfn + __pgcount may belong to a section that has not yet been initialized, causing page_ext_lookup() to trigger a NULL pointer dereference. [ 14.555124][ T846] Call trace: [ 14.555125][ T846] lookup_page_ext+0x6c/0x108 (P) [ 14.555127][ T846] page_ext_lookup+0x30/0x3c [ 14.555129][ T846] __reset_page_owner+0x11c/0x260 [ 14.571201][ T846] __free_pages_ok+0x5e8/0x8e0 [ 14.571204][ T846] __free_pages_core+0x78/0xf0 [ 14.571206][ T846] generic_online_page+0x14/0x24 [ 14.597782][ T846] online_pages+0x178/0x30c [ 14.597784][ T846] memory_block_change_state+0x284/0x32c [ 14.597787][ T846] memory_subsys_online+0x4c/0x64 [ 14.597789][ T846] device_online+0x88/0xb0 [ 14.597791][ T846] online_memory_block+0x30/0x40 [ 14.597793][ T846] walk_memory_blocks+0xac/0xe8 [ 14.597794][ T846] add_memory_resource+0x280/0x298 [ 14.656161][ T846] add_memory+0x60/0x98 Move the iteration boundary enforcement inside the iterator functions, so callers cannot inadvertently access beyond the requested range. Link: https://lore.kernel.org/20260623-page_ext-v3-1-a89799a5367c@oss.qualcomm.com Fixes: 9039b9096ea2 ("mm: page_ext: add an iteration API for page extensions") Signed-off-by: Ketan Kishore Suggested-by: David Hildenbrand Suggested-by: Matthew Wilcox Acked-by: Zi Yan Acked-by: David Hildenbrand (Arm) Cc: Brendan Jackman Cc: Johannes Weiner Cc: Liam R. Howlett Cc: Lorenzo Stoakes Cc: Luiz Capitulino Cc: Michal Hocko Cc: Mike Rapoport Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- include/linux/page_ext.h | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) --- a/include/linux/page_ext.h +++ b/include/linux/page_ext.h @@ -119,14 +119,18 @@ struct page_ext_iter { * page_ext_iter_begin() - Prepare for iterating through page extensions. * @iter: page extension iterator. * @pfn: PFN of the page we're interested in. + * @count: maximum number of page extensions to return. * * Must be called with RCU read lock taken. * * Return: NULL if no page_ext exists for this page. */ static inline struct page_ext *page_ext_iter_begin(struct page_ext_iter *iter, - unsigned long pfn) + unsigned long pfn, unsigned long count) { + if (!count) + return NULL; + iter->index = 0; iter->start_pfn = pfn; iter->page_ext = page_ext_lookup(pfn); @@ -137,19 +141,22 @@ static inline struct page_ext *page_ext_ /** * page_ext_iter_next() - Get next page extension * @iter: page extension iterator. + * @count: maximum number of page extensions to return. * * Must be called with RCU read lock taken. * * Return: NULL if no next page_ext exists. */ -static inline struct page_ext *page_ext_iter_next(struct page_ext_iter *iter) +static inline struct page_ext *page_ext_iter_next(struct page_ext_iter *iter, + unsigned long count) { unsigned long pfn; if (WARN_ON_ONCE(!iter->page_ext)) return NULL; - iter->index++; + if (++iter->index >= count) + return NULL; pfn = iter->start_pfn + iter->index; if (page_ext_iter_next_fast_possible(pfn)) @@ -182,9 +189,9 @@ static inline struct page_ext *page_ext_ * IMPORTANT: must be called with RCU read lock taken. */ #define for_each_page_ext(__page, __pgcount, __page_ext, __iter) \ - for (__page_ext = page_ext_iter_begin(&__iter, page_to_pfn(__page));\ - __page_ext && __iter.index < __pgcount; \ - __page_ext = page_ext_iter_next(&__iter)) + for (__page_ext = page_ext_iter_begin(&__iter, page_to_pfn(__page), __pgcount); \ + __page_ext; \ + __page_ext = page_ext_iter_next(&__iter, __pgcount)) #else /* !CONFIG_PAGE_EXTENSION */ struct page_ext;