From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 131784431 for ; Wed, 15 Mar 2023 12:28:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8C0B5C433EF; Wed, 15 Mar 2023 12:28:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1678883318; bh=Dh/qI2QJLDX/Q30gslNHpsglXEBVKKJrZ7k2TnGYmbA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=1cGNZyQgSlR2n3H19yrWU3CfZauiSS9xy1nVJaTPj2GL1SIUI+FzZRbJi5cQltQiw fgr1/DK9OfGH0Jd866q8V5Jceh3mK6dvNKxVrfiAuRDvvV9LtJlVVaPm+eUsJOKg4K ugFrJ7cbYPn/Bv0ZdP7czVREKkSaUYAZIM9cfmUQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Darrick J. Wong" , "Christian Brauner (Microsoft)" , Yang Xu , Amir Goldstein , Leah Rumancik , Sasha Levin , Jeff Layton Subject: [PATCH 5.15 098/145] fs: add mode_strip_sgid() helper Date: Wed, 15 Mar 2023 13:12:44 +0100 Message-Id: <20230315115742.209240395@linuxfoundation.org> X-Mailer: git-send-email 2.40.0 In-Reply-To: <20230315115738.951067403@linuxfoundation.org> References: <20230315115738.951067403@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Yang Xu commit 2b3416ceff5e6bd4922f6d1c61fb68113dd82302 upsream. Add a dedicated helper to handle the setgid bit when creating a new file in a setgid directory. This is a preparatory patch for moving setgid stripping into the vfs. The patch contains no functional changes. Currently the setgid stripping logic is open-coded directly in inode_init_owner() and the individual filesystems are responsible for handling setgid inheritance. Since this has proven to be brittle as evidenced by old issues we uncovered over the last months (see [1] to [3] below) we will try to move this logic into the vfs. Link: e014f37db1a2 ("xfs: use setattr_copy to set vfs inode attributes") [1] Link: 01ea173e103e ("xfs: fix up non-directory creation in SGID directories") [2] Link: fd84bfdddd16 ("ceph: fix up non-directory creation in SGID directories") [3] Link: https://lore.kernel.org/r/1657779088-2242-1-git-send-email-xuyang2018.jy@fujitsu.com Reviewed-by: Darrick J. Wong Reviewed-by: Christian Brauner (Microsoft) Reviewed-and-Tested-by: Jeff Layton Signed-off-by: Yang Xu Signed-off-by: Christian Brauner (Microsoft) Signed-off-by: Amir Goldstein Tested-by: Leah Rumancik Acked-by: Darrick J. Wong Signed-off-by: Sasha Levin --- fs/inode.c | 36 ++++++++++++++++++++++++++++++++---- include/linux/fs.h | 2 ++ 2 files changed, 34 insertions(+), 4 deletions(-) diff --git a/fs/inode.c b/fs/inode.c index 8279c700a2b7f..3740102c9bd5e 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -2165,10 +2165,8 @@ void inode_init_owner(struct user_namespace *mnt_userns, struct inode *inode, /* Directories are special, and always inherit S_ISGID */ if (S_ISDIR(mode)) mode |= S_ISGID; - else if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP) && - !in_group_p(i_gid_into_mnt(mnt_userns, dir)) && - !capable_wrt_inode_uidgid(mnt_userns, dir, CAP_FSETID)) - mode &= ~S_ISGID; + else + mode = mode_strip_sgid(mnt_userns, dir, mode); } else inode_fsgid_set(inode, mnt_userns); inode->i_mode = mode; @@ -2324,3 +2322,33 @@ struct timespec64 current_time(struct inode *inode) return timestamp_truncate(now, inode); } EXPORT_SYMBOL(current_time); + +/** + * mode_strip_sgid - handle the sgid bit for non-directories + * @mnt_userns: User namespace of the mount the inode was created from + * @dir: parent directory inode + * @mode: mode of the file to be created in @dir + * + * If the @mode of the new file has both the S_ISGID and S_IXGRP bit + * raised and @dir has the S_ISGID bit raised ensure that the caller is + * either in the group of the parent directory or they have CAP_FSETID + * in their user namespace and are privileged over the parent directory. + * In all other cases, strip the S_ISGID bit from @mode. + * + * Return: the new mode to use for the file + */ +umode_t mode_strip_sgid(struct user_namespace *mnt_userns, + const struct inode *dir, umode_t mode) +{ + if ((mode & (S_ISGID | S_IXGRP)) != (S_ISGID | S_IXGRP)) + return mode; + if (S_ISDIR(mode) || !dir || !(dir->i_mode & S_ISGID)) + return mode; + if (in_group_p(i_gid_into_mnt(mnt_userns, dir))) + return mode; + if (capable_wrt_inode_uidgid(mnt_userns, dir, CAP_FSETID)) + return mode; + + return mode & ~S_ISGID; +} +EXPORT_SYMBOL(mode_strip_sgid); diff --git a/include/linux/fs.h b/include/linux/fs.h index 1e1ac116dd136..be9be4a7216c7 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1941,6 +1941,8 @@ extern long compat_ptr_ioctl(struct file *file, unsigned int cmd, void inode_init_owner(struct user_namespace *mnt_userns, struct inode *inode, const struct inode *dir, umode_t mode); extern bool may_open_dev(const struct path *path); +umode_t mode_strip_sgid(struct user_namespace *mnt_userns, + const struct inode *dir, umode_t mode); /* * This is the "filldir" function type, used by readdir() to let -- 2.39.2