The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From fd84bfdddd169c219c3a637889a8b87f70a072c2 Mon Sep 17 00:00:00 2001
From: Christian Brauner christian.brauner@ubuntu.com Date: Mon, 29 Nov 2021 12:16:39 +0100 Subject: [PATCH] ceph: fix up non-directory creation in SGID directories
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
diff --git a/fs/ceph/file.c b/fs/ceph/file.c index b24442e27e4e..c138e8126286 100644 --- a/fs/ceph/file.c +++ b/fs/ceph/file.c @@ -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);