From: Amir Goldstein <amir73il@gmail.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Sasha Levin <sashal@kernel.org>,
"Darrick J . Wong" <djwong@kernel.org>,
Leah Rumancik <leah.rumancik@gmail.com>,
Chandan Babu R <chandan.babu@oracle.com>,
Christian Brauner <brauner@kernel.org>,
linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org,
stable@vger.kernel.org, Yang Xu <xuyang2018.jy@fujitsu.com>,
Jeff Layton <jlayton@kernel.org>
Subject: [PATCH 5.10 08/15] fs: add mode_strip_sgid() helper
Date: Sat, 18 Mar 2023 12:15:22 +0200 [thread overview]
Message-ID: <20230318101529.1361673-9-amir73il@gmail.com> (raw)
In-Reply-To: <20230318101529.1361673-1-amir73il@gmail.com>
From: Yang Xu <xuyang2018.jy@fujitsu.com>
commit 2b3416ceff5e6bd4922f6d1c61fb68113dd82302 upstream.
[remove userns argument of helper for 5.10.y backport]
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>
---
fs/inode.c | 34 ++++++++++++++++++++++++++++++----
include/linux/fs.h | 1 +
2 files changed, 31 insertions(+), 4 deletions(-)
diff --git a/fs/inode.c b/fs/inode.c
index 9f49e0bdc2f7..23d03abcb0ff 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2147,10 +2147,8 @@ void inode_init_owner(struct inode *inode, const struct inode *dir,
/* 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(inode->i_gid) &&
- !capable_wrt_inode_uidgid(dir, CAP_FSETID))
- mode &= ~S_ISGID;
+ else
+ mode = mode_strip_sgid(dir, mode);
} else
inode->i_gid = current_fsgid();
inode->i_mode = mode;
@@ -2382,3 +2380,31 @@ int vfs_ioc_fssetxattr_check(struct inode *inode, const struct fsxattr *old_fa,
return 0;
}
EXPORT_SYMBOL(vfs_ioc_fssetxattr_check);
+
+/**
+ * mode_strip_sgid - handle the sgid bit for non-directories
+ * @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(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(dir->i_gid))
+ return mode;
+ if (capable_wrt_inode_uidgid(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 74e19bccbf73..527791e4860b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1768,6 +1768,7 @@ extern long compat_ptr_ioctl(struct file *file, unsigned int cmd,
extern void inode_init_owner(struct inode *inode, const struct inode *dir,
umode_t mode);
extern bool may_open_dev(const struct path *path);
+umode_t mode_strip_sgid(const struct inode *dir, umode_t mode);
/*
* This is the "filldir" function type, used by readdir() to let
--
2.34.1
next prev parent reply other threads:[~2023-03-18 10:16 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-18 10:15 [PATCH 5.10 00/15] xfs backports for 5.10.y (from v5.15.103) Amir Goldstein
2023-03-18 10:15 ` [PATCH 5.10 01/15] xfs: don't assert fail on perag references on teardown Amir Goldstein
2023-03-18 10:15 ` [PATCH 5.10 02/15] xfs: purge dquots after inode walk fails during quotacheck Amir Goldstein
2023-03-18 10:15 ` [PATCH 5.10 03/15] xfs: don't leak btree cursor when insrec fails after a split Amir Goldstein
2023-03-18 10:15 ` [PATCH 5.10 04/15] xfs: remove XFS_PREALLOC_SYNC Amir Goldstein
2023-03-18 10:15 ` [PATCH 5.10 05/15] xfs: fallocate() should call file_modified() Amir Goldstein
2023-03-18 10:15 ` [PATCH 5.10 06/15] xfs: set prealloc flag in xfs_alloc_file_space() Amir Goldstein
2023-03-18 10:15 ` [PATCH 5.10 07/15] xfs: use setattr_copy to set vfs inode attributes Amir Goldstein
2023-03-18 10:15 ` Amir Goldstein [this message]
2023-03-18 10:15 ` [PATCH 5.10 09/15] fs: move S_ISGID stripping into the vfs_*() helpers Amir Goldstein
2023-03-18 10:15 ` [PATCH 5.10 10/15] attr: add in_group_or_capable() Amir Goldstein
2023-03-18 10:15 ` [PATCH 5.10 11/15] fs: move should_remove_suid() Amir Goldstein
2023-03-18 10:15 ` [PATCH 5.10 12/15] attr: add setattr_should_drop_sgid() Amir Goldstein
2023-03-18 10:15 ` [PATCH 5.10 13/15] attr: use consistent sgid stripping checks Amir Goldstein
2023-03-18 10:15 ` [PATCH 5.10 14/15] fs: use consistent setgid checks in is_sxid() Amir Goldstein
2023-03-18 10:15 ` [PATCH 5.10 15/15] xfs: remove xfs_setattr_time() declaration Amir Goldstein
2023-03-20 14:13 ` [PATCH 5.10 00/15] xfs backports for 5.10.y (from v5.15.103) Greg Kroah-Hartman
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