From nobody Fri Dec 19 11:49:56 2025 Received: from mail-oo1-f69.google.com (mail-oo1-f69.google.com [209.85.161.69]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5BBC2208D0 for ; Sun, 7 Dec 2025 12:44:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.161.69 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765111491; cv=none; b=qVovoTEZFMGt2vyI4crZeRtEomfTYGu591doYaZGRNQumX7USdJoK+mcUKwrgeY6N1pfvgI4Kg7C3lDaIR3yDTCFbCQeKPqiO37zWxNDx5IvjKh+mF6qFV1xbKHoNjSF5m9ATe7MHR45kUE2D1EJFfzV7sS7uHG9UUhdiM8GNZo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765111491; c=relaxed/simple; bh=VtCYHXAV5UjRZRp+jr82H5rCZ40J6PiuGG7DGS6nj6E=; h=MIME-Version:Date:In-Reply-To:Message-ID:Subject:From:To: Content-Type; b=PmZS9BEaIu7oIMg1XI/iTSzIUeqhFZMFGGB3cVfT3CxrgA6nxJN/zVGgOKJKQkracMG6a2SNVAySqZyvySDmkKorMAxljfmAznS66A8Cxz+9MYT0TMAK7maG6tT9BKAziA7sgUoZsGAPUUfEWDSbx3GCb1WNGjgtflq1FDWN5vM= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com; arc=none smtp.client-ip=209.85.161.69 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=syzkaller.appspotmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=M3KW2WVRGUFZ5GODRSRYTGD7.apphosting.bounces.google.com Received: by mail-oo1-f69.google.com with SMTP id 006d021491bc7-656cc4098f3so4632532eaf.2 for ; Sun, 07 Dec 2025 04:44:50 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1765111489; x=1765716289; h=to:from:subject:message-id:in-reply-to:date:mime-version :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=t9OBx+5Uo/RNTziKfwgro/T7keoJ6v1qavte2AU2oe0=; b=PtBP9Gzj5KCJWSXcQH1PdgKhakKh6U+1HpoXwX71tclBYPs8BIoF1Ktl2fPLrPLvHS EHyhLNEIquyuBsWuzHHkVLuP+U+/Pjgve1kzrBAuW6KqtLhrLrfNGb1Q8WnLmRnXItRx R4VgiDuYUTotGbru+vU8o9aAtHpBE7VxtThx7knIGD+ky7dcMyQBbUz8dSDxB/3IGEgg +Mmntw6K60gTf8rojz0CEjwuUBGx523jDqbH+3lasP9E0yJQZtvnCLCF/o5V2zxiWUbf ybdLW0WBuOTlgpgfrtfWEKHG5VFTi6j4nYa+kT7WzHJtOuDYMrbdm1Gu+ZnYlcX2LT4g VgLA== X-Gm-Message-State: AOJu0YxrjtQk70on3DioagGTxARkdb5478yjDhaWOQz9BYVmLu+d+lLi 3cMrJd99JyJxaBTAvzteut0U4w+IiF8KLNH0sknj556CkyIiTjpsi4ANN+pmjNzmkPbLidvYxaU vXxqCDE1pqLU/KpCqoagrhPUIDfY+Ql5MFmvACandCB2XFvvp4AtBfsQE9f4= X-Google-Smtp-Source: AGHT+IHv6mb6MlZ3vTja3gu3OkuEiycS59IAZWAQ0FcQT7P51gfsXE5DnUkrMNUtQwbB/EFTD75swa07HDslnM0p+5MYJkiPxp+9 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Received: by 2002:a05:6820:16a6:b0:659:9a49:9005 with SMTP id 006d021491bc7-6599a9648c2mr2252038eaf.50.1765111489373; Sun, 07 Dec 2025 04:44:49 -0800 (PST) Date: Sun, 07 Dec 2025 04:44:49 -0800 In-Reply-To: <693540fe.a70a0220.38f243.004c.GAE@google.com> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <693576c1.a70a0220.38f243.0050.GAE@google.com> Subject: Forwarded: [PATCH] mm/workingset: fix NULL pointer dereference in lru_gen_test_recent From: syzbot To: linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" For archival purposes, forwarding an incoming command email to linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com. *** Subject: [PATCH] mm/workingset: fix NULL pointer dereference in lru_gen_tes= t_recent Author: kartikey406@gmail.com #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git= master Add NULL check for memcg in lru_gen_test_recent() to prevent crash when mem_cgroup_from_id() returns NULL. The crash occurs when a folio's shadow entry contains a memcg_id that no longer maps to a valid memory cgroup. This can happen when: 1. The memory cgroup has been deleted/freed 2. A folio was created without proper memcg association (e.g., during procmap_query build ID parsing via freader_get_folio) 3. The memcg_id in the shadow entry is invalid or zero When lru_gen_test_recent() calls mem_cgroup_from_id(), it may return NULL. The subsequent call to mem_cgroup_lruvec() with a NULL memcg triggers a crash because the inline function's code calculates memcg->nodeinfo offset (0x4e00) before the NULL check can execute, causing a NULL pointer dereference that KASAN detects. Although mem_cgroup_lruvec() has a NULL check internally, compiler inlining and optimization causes the offset calculation to occur first, making the internal check unreachable. The fix adds an explicit NULL check after mem_cgroup_from_id() and falls back to root_mem_cgroup, which is consistent with how mem_cgroup_lruvec() itself handles NULL pointers. Reproducer triggers this via: procfs_procmap_ioctl() -> do_procmap_query() -> __build_id_parse() -> freader_get_folio() -> filemap_add_folio() -> workingset_refault() -> lru_gen_refault() -> lru_gen_test_recent() KASAN report: general protection fault in mem_cgroup_lruvec RIP: mem_cgroup_lruvec+0xee/0x320 include/linux/memcontrol.h:720 Call Trace: lru_gen_test_recent+0xee/0x320 mm/workingset.c:275 workingset_refault+0x251/0xca0 mm/workingset.c:546 filemap_add_folio+0x23d/0x610 mm/filemap.c:981 Reported-by: syzbot+e008db2ac01e282550ee@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3De008db2ac01e282550ee Signed-off-by: Deepanshu Kartikey --- mm/workingset.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/workingset.c b/mm/workingset.c index e9f05634747a..8b6332cfb4f0 100644 --- a/mm/workingset.c +++ b/mm/workingset.c @@ -272,6 +272,8 @@ static bool lru_gen_test_recent(void *shadow, struct lr= uvec **lruvec, unpack_shadow(shadow, &memcg_id, &pgdat, token, workingset); =20 memcg =3D mem_cgroup_from_id(memcg_id); + if (!memcg) + memcg =3D root_mem_cgroup; *lruvec =3D mem_cgroup_lruvec(memcg, pgdat); =20 max_seq =3D READ_ONCE((*lruvec)->lrugen.max_seq); --=20 2.43.0