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 D3D9F4334A9 for ; Thu, 3 Sep 2026 12:22:34 +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=1788438156; cv=none; b=VK7axwyjjEgDylVIDd5OdZtfcpYl8NaOxRIWtzzuI+ZcBBEKhiC1I03HG6hKeaz9TvtoPEOYOXVJvxs5sHdDhue5xoGYzHCE8Zu1giMMpCyCLzsEG8qdHrNpjh90DEbHmP8I7RQ1ssUHO9TQ3ABAnz8HIxXRfSpC5Uu9K+bM47c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788438156; c=relaxed/simple; bh=b9piot4jxvXQpCVDm0RflqIq4B2djWQB5kgiGbMx0Mg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=SEffxhh0FZEiUXNaxXF7HleSovbIK8bGj650d+/c38LEN83HA7ES9HDkUtthZ7l1LLVkOjzgXTawpf/qTA2Ux0g9XHr6O9U9L5txkp5yfH0AToApFnTNoHg/3t8rxAsFmaAOHiMaj3DHfBUOv1jI+tbvAiZYw8+eTV9r+Hv+WpE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=YboejKQW; 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="YboejKQW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C5AB31F000E9; Thu, 3 Sep 2026 12:22:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788438154; bh=ftQqE+BPPVyoLQuDQc8eObNjSD68owUglOnYCKVEhr4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=YboejKQWNhI21bRnvG5ZiT+rBvyHKu0/nSRB1eJfV17wGS2rRpjRJUjAcu63j54Yj fYO7ehVg0mQqJWHXrWftWsjU4qVs9yBkuSS1OqHOd7iGVLrF/Y2HjCHPWIZ8JoW4JU npTrYsXgguHtOtdItZ15VQzwO4vERCHAHpJXIXiW8Mdui2odbEMqfi9iAQ7dx56PBW 0UPk/9LK4INJVoi8c373Iieh/oNz/ucKlDxJOkK1s+P7fsl7wFRAzCETx9/QnaR6mj O0UFtRXJpTOImol+sgDIj7tNd0z27k6+7r6HPkxG1uVh/eU4V413F61UEY+PVdSahf UuchI+vmwCTRw== From: Sasha Levin To: stable@vger.kernel.org Cc: Vivek Parikh , Amir Goldstein , "Christian Brauner (Amutable)" , Sasha Levin Subject: [PATCH 6.18.y] ovl: fix double end_creating() on the casefold-mismatch path Date: Thu, 3 Sep 2026 08:22:32 -0400 Message-ID: <20260903122232.708987-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026090319-clanking-sandstone-d89f@gregkh> References: <2026090319-clanking-sandstone-d89f@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Vivek Parikh [ Upstream commit 077ab8985ee278c3d8618182d335b0f0cd919e16 ] ovl_create_real() releases the new dentry twice when the casefold consistency check fails. The S_IFDIR branch calls end_creating() and sets err, then falls through to the common out: label which calls end_creating() on the same dentry again: case S_IFDIR: newdentry = ovl_do_mkdir(ofs, dir, newdentry, attr->mode); err = PTR_ERR_OR_ZERO(newdentry); if (!err && ofs->casefold != ovl_dentry_casefolded(newdentry)) { pr_warn_ratelimited(...); end_creating(newdentry); /* first */ err = -EINVAL; } break; ... if (err) goto out; ... out: if (err) { end_creating(newdentry); /* second, same dentry */ return ERR_PTR(err); } end_creating() is end_dirop(), which does inode_unlock() on the parent and dput() on the dentry, so the parent directory's i_rwsem is unlocked twice and the dentry is put twice. The second unlock releases a lock that is not held, which is what wedges every later creation under that parent, and the second dput() drops a reference that was never taken. The branch was added by commit dfc7da402ccc ("ovl: Check for casefold consistency when creating new dentries") as a bare dput(), which already released the reference twice; commit fe497f0759e0 ("VFS: change vfs_mkdir() to unlock on failure.") converted both sites to end_creating(), adding the double unlock. This is reachable by an unprivileged user. The casefold consistency of the layers is validated at mount time in ovl_parse_layer(), and again on every lookup in ovl_lookup_single(), but ofs->workdir is the internal "work" subdirectory created inside the user-supplied workdir, and that subdirectory is not re-checked. Marking it casefolded after the mount therefore makes every ovl_create_temp() inherit the wrong state - and that path reaches ovl_create_real() through ovl_start_creating_temp(), which uses start_creating() with a generated name and so never runs the lookup-time check. unshare -Urm mount -t tmpfs -o casefold=utf8-12.1.0 tmpfs mnt mkdir -p mnt/lower/d mnt/upper mnt/work mnt/merged mount -t overlay ovl -o lowerdir=mnt/lower,\ upperdir=mnt/upper,workdir=mnt/work mnt/merged chattr +F mnt/work/work mkdir mnt/merged/d/sub # directory copy-up overlayfs: wrong inherited casefold (work/#5) and the next copy-up blocks forever on the parent's i_rwsem: mkdir D start_creating+0x65/0xb0 ovl_start_creating_temp+0xb0/0xe0 [overlay] ovl_create_temp+0xa3/0x1d0 [overlay] ovl_copy_up_one+0x1f1c/0x21c0 [overlay] ovl_copy_up_flags+0xf5/0x140 [overlay] ovl_create_object+0xb7/0x220 [overlay] ovl_mkdir+0x23/0x40 [overlay] Drop the end_creating() from the branch and let out: own the cleanup, which is what every other error path in this function already does. Fixes: dfc7da402ccc ("ovl: Check for casefold consistency when creating new dentries") Cc: stable@vger.kernel.org Signed-off-by: Vivek Parikh Reviewed-by: Amir Goldstein Signed-off-by: Christian Brauner (Amutable) [ adapted end_creating() cleanup removal to the older dput() API ] Signed-off-by: Sasha Levin --- fs/overlayfs/dir.c | 1 - 1 file changed, 1 deletion(-) diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c index e924321b64025..1abe533304ba4 100644 --- a/fs/overlayfs/dir.c +++ b/fs/overlayfs/dir.c @@ -191,7 +191,6 @@ struct dentry *ovl_create_real(struct ovl_fs *ofs, struct dentry *parent, if (!err && ofs->casefold != ovl_dentry_casefolded(newdentry)) { pr_warn_ratelimited("wrong inherited casefold (%pd2)\n", newdentry); - dput(newdentry); err = -EINVAL; } break; -- 2.53.0