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ceph: fix up non-directory creation in SGID directories

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Ceph always inherits the SGID bit if it is set on the parent inode,
while the generic inode_init_owner does not do this in a few cases where
it can create a possible security problem (cf. [1]).

Update ceph to strip the SGID bit just as inode_init_owner would.

This bug was detected by the mapped mount testsuite in [3]. The
testsuite tests all core VFS functionality and semantics with and
without mapped mounts. That is to say it functions as a generic VFS
testsuite in addition to a mapped mount testsuite. While working on
mapped mount support for ceph, SIGD inheritance was the only failing
test for ceph after the port.

The same bug was detected by the mapped mount testsuite in XFS in
January 2021 (cf. [2]).

[1]: commit 0fa3ecd878 ("Fix up non-directory creation in SGID directories")
[2]: commit 01ea173e10 ("xfs: fix up non-directory creation in SGID directories")
[3]: https://git.kernel.org/fs/xfs/xfstests-dev.git

Cc: stable@vger.kernel.org
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
This commit is contained in:
Christian Brauner 2021-11-29 12:16:39 +01:00 committed by Ilya Dryomov
parent ee2a095d3b
commit fd84bfdddd
1 changed files with 15 additions and 3 deletions
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18
fs/ceph/file.c
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@ -605,13 +605,25 @@ static int ceph_finish_async_create(struct inode *dir, struct dentry *dentry,
in.cap.realm = cpu_to_le64(ci->i_snap_realm->ino);
in.cap.flags = CEPH_CAP_FLAG_AUTH;
in.ctime = in.mtime = in.atime = iinfo.btime;
in.mode = cpu_to_le32((u32)mode);
in.truncate_seq = cpu_to_le32(1);
in.truncate_size = cpu_to_le64(-1ULL);
in.xattr_version = cpu_to_le64(1);
in.uid = cpu_to_le32(from_kuid(&init_user_ns, current_fsuid()));
in.gid = cpu_to_le32(from_kgid(&init_user_ns, dir->i_mode & S_ISGID ?
dir->i_gid : current_fsgid()));
if (dir->i_mode & S_ISGID) {
in.gid = cpu_to_le32(from_kgid(&init_user_ns, dir->i_gid));
/* Directories always inherit the setgid bit. */
if (S_ISDIR(mode))
mode |= S_ISGID;
else if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP) &&
!in_group_p(dir->i_gid) &&
!capable_wrt_inode_uidgid(&init_user_ns, dir, CAP_FSETID))
mode &= ~S_ISGID;
} else {
in.gid = cpu_to_le32(from_kgid(&init_user_ns, current_fsgid()));
}
in.mode = cpu_to_le32((u32)mode);
in.nlink = cpu_to_le32(1);
in.max_size = cpu_to_le64(lo->stripe_unit);