| Message ID | 20180523232538.4880-1-ebiederm@xmission.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, May 23, 2018 at 06:25:33PM -0500, Eric W. Biederman wrote: > Changing the link count of an inode via unlink or link will cause a > write back of that inode. If the uids or gids are invalid (aka not known > to the kernel) writing the inode back may change the uid or gid in the > filesystem. To prevent possible filesystem and to avoid the need for > filesystem maintainers to worry about it don't allow operations on > inodes with an invalid uid or gid. > > Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> Acked-by: Seth Forshee <seth.forshee@canonical.com>
On Thu, May 24, 2018 at 07:58:32AM -0500, Seth Forshee wrote: > On Wed, May 23, 2018 at 06:25:33PM -0500, Eric W. Biederman wrote: > > Changing the link count of an inode via unlink or link will cause a > > write back of that inode. If the uids or gids are invalid (aka not known > > to the kernel) writing the inode back may change the uid or gid in the > > filesystem. To prevent possible filesystem and to avoid the need for > > filesystem maintainers to worry about it don't allow operations on > > inodes with an invalid uid or gid. > > > > Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> > > Acked-by: Seth Forshee <seth.forshee@canonical.com> Acked-by: Christian Brauner <christian@brauner.io>
diff --git a/fs/namei.c b/fs/namei.c index 186bd2464fd5..942c1f096f6b 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -984,13 +984,15 @@ static bool safe_hardlink_source(struct inode *inode) */ static int may_linkat(struct path *link) { - struct inode *inode; + struct inode *inode = link->dentry->d_inode; + + /* Inode writeback is not safe when the uid or gid are invalid. */ + if (!uid_valid(inode->i_uid) || !gid_valid(inode->i_gid)) + return -EOVERFLOW; if (!sysctl_protected_hardlinks) return 0; - inode = link->dentry->d_inode; - /* Source inode owner (or CAP_FOWNER) can hardlink all they like, * otherwise, it must be a safe source. */ @@ -2749,6 +2751,11 @@ static int may_delete(struct inode *dir, struct dentry *victim, bool isdir) BUG_ON(!inode); BUG_ON(victim->d_parent->d_inode != dir); + + /* Inode writeback is not safe when the uid or gid are invalid. */ + if (!uid_valid(inode->i_uid) || !gid_valid(inode->i_gid)) + return -EOVERFLOW; + audit_inode_child(dir, victim, AUDIT_TYPE_CHILD_DELETE); error = inode_permission(dir, MAY_WRITE | MAY_EXEC);
Changing the link count of an inode via unlink or link will cause a write back of that inode. If the uids or gids are invalid (aka not known to the kernel) writing the inode back may change the uid or gid in the filesystem. To prevent possible filesystem and to avoid the need for filesystem maintainers to worry about it don't allow operations on inodes with an invalid uid or gid. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> --- fs/namei.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)