From: Christian Brauner christian.brauner@ubuntu.com
commit fd84bfdddd169c219c3a637889a8b87f70a072c2 upstream.
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 0fa3ecd87848 ("Fix up non-directory creation in SGID directories") [2]: commit 01ea173e103e ("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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/ceph/file.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-)
--- a/fs/ceph/file.c +++ b/fs/ceph/file.c @@ -603,13 +603,25 @@ static int ceph_finish_async_create(stru 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);