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 E1BC93B8124; Sat, 17 Oct 2026 16:40:48 +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=1792255250; cv=none; b=kGy+oCcPi4mCtYyw/wbrfcUvhHHR5HF6VhjClMI6LGgkCzFqevyC7nmOud06Z3eO27QCMV+G30iT4TVaXwIQvoFSFHRCi0PLm8V2kOW4QWFFD6isVWMCvfDnDLuFQ0etdnDeP4BfGCtqmApkZ0NuGuuNp24QFsuXbzfntnUmaV8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792255250; c=relaxed/simple; bh=la6wQiPVnbbnFIcsLwabCdTrtNOPnp+/3ib+3wymmDM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=O3sBU5Cn7XL4szVPofdlqHGv11u0MnTE7nm78G0J/euvVz1vjaJVaMLn5lEklIeLXVJ19kz5V3msvxCSTAkd/ub3AIPWCksSbwdTWfGRxonQ/DPY1g+nBahmR15RdnFFcmoBrx0ZXc+rbquPL3iNl3zRYubtuXIT8/Icpqw0mJQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=GJAmy0z4; 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="GJAmy0z4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 34B271F000C4; Sat, 17 Oct 2026 16:40:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1792255248; bh=eV5BhbjV2vFyXzZYPzBx1eYpBSILXidJcEnvlN5JbWE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=GJAmy0z4Awl5yikXdLW3V5u4uxpoFR48Vn0YS6t+F9h17JraAAx3v3nWXn3T/0eL7 d+Ipseki2Z9+rKnO82xlH6i6jGM3oiD0Xh1OozhjAzDpMnsKy8kwPLV+H6lunLZLy9 dCcoBu5U2exboZpZLqlTpnzhbkbSV87dSPHynO7c= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Ye Liu , Sashiko , Zi Yan , "Vlastimil Babka (SUSE)" , Brendan Jackman , Johannes Weiner , Lorenzo Stoakes , Michal Hocko , Suren Baghdasaryan , "David Hildenbrand (Arm)" , Andrew Morton , Sasha Levin Subject: [PATCH 6.12 715/869] mm/page_owner: use memcg_data snapshot to avoid TOCTOU in print_page_owner_memcg() Date: Sat, 17 Oct 2026 17:59:16 +0200 Message-ID: <20261017160055.290607960@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261017160036.979869304@linuxfoundation.org> References: <20261017160036.979869304@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 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ye Liu [ Upstream commit 90f095b816e25c6a9e4446d299bac5007fdcb3df ] print_page_owner_memcg() reads page->memcg_data via READ_ONCE() at the start to guard against tail pages and NULL data. However, it later re-reads page->memcg_data locklessly in two places: 1: page_memcg_check(page) 2: PageMemcgKmem(page) (via folio_memcg_kmem(), which includes VM_BUG_ON assertions for tail pages and MEMCG_DATA_OBJEXTS) If the page is concurrently freed and reallocated as a THP tail page or slab page between these calls, the VM_BUG_ON assertions can trigger on CONFIG_DEBUG_VM=y builds, crashing the kernel. Fix both TOCTOU issues by using the memcg_data snapshot throughout. Link: https://lore.kernel.org/20260714015117.78351-10-ye.liu@linux.dev Fixes: fcf8935832b8 ("mm/page_owner: print memcg information") Signed-off-by: Ye Liu Reported-by: Sashiko Reviewed-by: Zi Yan Reviewed-by: Vlastimil Babka (SUSE) Cc: Brendan Jackman Cc: Johannes Weiner Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Suren Baghdasaryan Cc: David Hildenbrand (Arm) Cc: Signed-off-by: Andrew Morton Signed-off-by: Sasha Levin --- mm/page_owner.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/mm/page_owner.c b/mm/page_owner.c index f92cec789eee5..5d1c946c0008f 100644 --- a/mm/page_owner.c +++ b/mm/page_owner.c @@ -501,6 +501,7 @@ static inline int print_page_owner_memcg(char *kbuf, size_t count, int ret, { #ifdef CONFIG_MEMCG unsigned long memcg_data; + struct obj_cgroup *objcg; struct mem_cgroup *memcg; bool online; char name[80]; @@ -510,11 +511,14 @@ static inline int print_page_owner_memcg(char *kbuf, size_t count, int ret, if (!memcg_data) goto out_unlock; - if (memcg_data & MEMCG_DATA_OBJEXTS) + if (memcg_data & MEMCG_DATA_OBJEXTS) { ret += scnprintf(kbuf + ret, count - ret, "Slab cache page\n"); + goto out_unlock; + } - memcg = page_memcg_check(page); + objcg = (void *)(memcg_data & ~OBJEXTS_FLAGS_MASK); + memcg = objcg ? obj_cgroup_memcg(objcg) : NULL; if (!memcg) goto out_unlock; @@ -522,7 +526,7 @@ static inline int print_page_owner_memcg(char *kbuf, size_t count, int ret, cgroup_name(memcg->css.cgroup, name, sizeof(name)); ret += scnprintf(kbuf + ret, count - ret, "Charged %sto %smemcg %s\n", - PageMemcgKmem(page) ? "(via objcg) " : "", + (memcg_data & MEMCG_DATA_KMEM) ? "(via objcg) " : "", online ? "" : "offline ", name); out_unlock: -- 2.53.0