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 E9AAC31E823 for ; Thu, 3 Sep 2026 23:50:19 +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=1788479421; cv=none; b=Hgns5dXbSZ5u0nywgaNZ2yMGpkmBCEZRo9i2eG+doHSVxUGVpakOmP1QpC3okBLroOIHsTrNGiMkNemQ50YlLXnQBy9DElrTGelTo+1oE1G3he4p7lN58ssWb+/aelYVROaXx9YRfQFdaCSrRsDGIYXcmO2ND6jHgposX+8sGaw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788479421; c=relaxed/simple; bh=hppceOpWXiCC7EqCtZd1R6pLABgHvNnChLrbRyiLF/A=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=KxZc0j3MeZf0WACKPmdGwphrqb+L/HDT0aHFjrlbyX8Ze5LrtQZAuTmll7D/Cc0GQs1tK4iQ0LaUC1h47vpVl6aQ5xKWsT1lD+4FTo3F9nc9FW6JOJPSU87BhDJtyRccXw8ml4QCjN8U2bTkuWOBBwA2xgImEygljv+pnNgNcGM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=kLI1xRJc; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="kLI1xRJc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 466DF1F00A3D; Thu, 3 Sep 2026 23:50:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788479419; bh=/7NUdW/hMwX+Ft52klzjW8ibceNApwTOHTPTfCH+5g8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=kLI1xRJceX8D3Dq2k7ExNYUibgNSTTQhfeaxOdnfYwzvfEN4CtHHoGtlvihQL+sT/ OFhqaoKnidep4eXPYrjijvITFl4OEvE7mrzILC2ja/g7I82ENFCPc9YbKE6aWvBVNN bcvtGLjJLe4+GsBdsOgtqKM4FczCnF0Bj5x8vJJRFwMZl/OmIDSlJ1vR2pNjSNvfcq KL2PURDLe1sxfLFooqGous1JH1LhoeuM6wNii/ZJydzUkmqYq6SlL05vl9dBNm/VMG HgkHPbO7pQFq6GC3orqVKNZIEAUER1agh0vcUNfHpDuNowI3ykVFY9QwqQaS26IqdN /Kf8+piy6Q0EQ== From: Sasha Levin To: stable@vger.kernel.org Cc: 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 6.6.y] mm/page_owner: use memcg_data snapshot to avoid TOCTOU in print_page_owner_memcg() Date: Thu, 3 Sep 2026 19:50:16 -0400 Message-ID: <20260903235016.1804338-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026090314-dayroom-oblong-b702@gregkh> References: <2026090314-dayroom-oblong-b702@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 [ adapted memcg_data decoding to Linux 6.6’s mixed mem_cgroup and obj_cgroup representation. ] Signed-off-by: Sasha Levin --- mm/page_owner.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/mm/page_owner.c b/mm/page_owner.c index 4e2723e1b300d..e76bd0fad80ee 100644 --- a/mm/page_owner.c +++ b/mm/page_owner.c @@ -363,20 +363,28 @@ 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]; rcu_read_lock(); memcg_data = READ_ONCE(page->memcg_data); - if (!memcg_data) + if (!memcg_data || PageTail(page)) goto out_unlock; - if (memcg_data & MEMCG_DATA_OBJCGS) + if (memcg_data & MEMCG_DATA_OBJCGS) { ret += scnprintf(kbuf + ret, count - ret, "Slab cache page\n"); + goto out_unlock; + } - memcg = page_memcg_check(page); + if (memcg_data & MEMCG_DATA_KMEM) { + objcg = (void *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK); + memcg = objcg ? obj_cgroup_memcg(objcg) : NULL; + } else { + memcg = (void *)(memcg_data & ~MEMCG_DATA_FLAGS_MASK); + } if (!memcg) goto out_unlock; @@ -384,7 +392,7 @@ 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