From: Leah Rumancik <leah.rumancik@gmail.com>
To: stable@vger.kernel.org
Cc: linux-xfs@vger.kernel.org, amir73il@gmail.com,
chandan.babu@oracle.com, Yang Xu <xuyang2018.jy@fujitsu.com>,
"Darrick J . Wong" <djwong@kernel.org>,
Christian Brauner <brauner@kernel.org>,
Jeff Layton <jlayton@kernel.org>,
Leah Rumancik <leah.rumancik@gmail.com>
Subject: [PATCH 5.15 05/11] fs: add mode_strip_sgid() helper
Date: Tue, 7 Mar 2023 10:59:16 -0800 [thread overview]
Message-ID: <20230307185922.125907-6-leah.rumancik@gmail.com> (raw)
In-Reply-To: <20230307185922.125907-1-leah.rumancik@gmail.com>
From: Yang Xu <xuyang2018.jy@fujitsu.com>
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 <djwong@kernel.org>
Reviewed-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Reviewed-and-Tested-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Yang Xu <xuyang2018.jy@fujitsu.com>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Tested-by: Leah Rumancik <leah.rumancik@gmail.com>
Acked-by: Darrick J. Wong <djwong@kernel.org>
---
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 8279c700a2b7..3740102c9bd5 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 1e1ac116dd13..be9be4a7216c 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
--
2.40.0.rc0.216.gc4246ad0f0-goog
next prev parent reply other threads:[~2023-03-07 19:16 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-07 18:59 [PATCH 5.15 00/11] sgid fixes for 5.15.y Leah Rumancik
2023-03-07 18:59 ` [PATCH 5.15 01/11] xfs: use setattr_copy to set vfs inode attributes Leah Rumancik
2023-03-07 18:59 ` [PATCH 5.15 02/11] xfs: remove XFS_PREALLOC_SYNC Leah Rumancik
2023-03-07 18:59 ` [PATCH 5.15 03/11] xfs: fallocate() should call file_modified() Leah Rumancik
2023-03-07 18:59 ` [PATCH 5.15 04/11] xfs: set prealloc flag in xfs_alloc_file_space() Leah Rumancik
2023-03-07 18:59 ` Leah Rumancik [this message]
2023-03-07 18:59 ` [PATCH 5.15 06/11] fs: move S_ISGID stripping into the vfs_*() helpers Leah Rumancik
2023-03-07 18:59 ` [PATCH 5.15 07/11] attr: add in_group_or_capable() Leah Rumancik
2023-03-07 18:59 ` [PATCH 5.15 08/11] fs: move should_remove_suid() Leah Rumancik
2023-03-07 18:59 ` [PATCH 5.15 09/11] attr: add setattr_should_drop_sgid() Leah Rumancik
2023-03-07 18:59 ` [PATCH 5.15 10/11] attr: use consistent sgid stripping checks Leah Rumancik
2023-03-07 18:59 ` [PATCH 5.15 11/11] fs: use consistent setgid checks in is_sxid() Leah Rumancik
2023-03-14 2:16 ` [PATCH 5.15 00/11] sgid fixes for 5.15.y Sasha Levin
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