proc: Better ownership of files for non-dumpable tasks in user namespaces

Instead of making the files owned by the GLOBAL_ROOT_USER.  Make
non-dumpable files whose mm has always lived in a user namespace owned
by the user namespace root.  This allows the container root to have
things work as expected in a container.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

1 files changed, 58 insertions, 44 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 8e7e61b28f31..ad98d883847a 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1667,12 +1667,63 @@ const struct inode_operations proc_pid_link_inode_operations = {
 
 /* building an inode */
 
+void task_dump_owner(struct task_struct *task, mode_t mode,
+                     kuid_t *ruid, kgid_t *rgid)
+{
+        /* Depending on the state of dumpable compute who should own a
+         * proc file for a task.
+         */
+        const struct cred *cred;
+        kuid_t uid;
+        kgid_t gid;
+
+        /* Default to the tasks effective ownership */
+        rcu_read_lock();
+        cred = __task_cred(task);
+        uid = cred->euid;
+        gid = cred->egid;
+        rcu_read_unlock();
+
+        /*
+         * Before the /proc/pid/status file was created the only way to read
+         * the effective uid of a /process was to stat /proc/pid.  Reading
+         * /proc/pid/status is slow enough that procps and other packages
+         * kept stating /proc/pid.  To keep the rules in /proc simple I have
+         * made this apply to all per process world readable and executable
+         * directories.
+         */
+        if (mode != (S_IFDIR|S_IRUGO|S_IXUGO)) {
+                struct mm_struct *mm;
+                task_lock(task);
+                mm = task->mm;
+                /* Make non-dumpable tasks owned by some root */
+                if (mm) {
+                        if (get_dumpable(mm) != SUID_DUMP_USER) {
+                                struct user_namespace *user_ns = mm->user_ns;
+
+                                uid = make_kuid(user_ns, 0);
+                                if (!uid_valid(uid))
+                                        uid = GLOBAL_ROOT_UID;
+
+                                gid = make_kgid(user_ns, 0);
+                                if (!gid_valid(gid))
+                                        gid = GLOBAL_ROOT_GID;
+                        }
+                } else {
+                        uid = GLOBAL_ROOT_UID;
+                        gid = GLOBAL_ROOT_GID;
+                }
+                task_unlock(task);
+        }
+        *ruid = uid;
+        *rgid = gid;
+}
+
 struct inode *proc_pid_make_inode(struct super_block * sb,
                                   struct task_struct *task, umode_t mode)
 {
         struct inode * inode;
         struct proc_inode *ei;
-        const struct cred *cred;
 
         /* We need a new inode */
 
@@ -1694,13 +1745,7 @@ struct inode *proc_pid_make_inode(struct super_block * sb,
         if (!ei->pid)
                 goto out_unlock;
 
-        if (task_dumpable(task)) {
-                rcu_read_lock();
-                cred = __task_cred(task);
-                inode->i_uid = cred->euid;
-                inode->i_gid = cred->egid;
-                rcu_read_unlock();
-        }
+        task_dump_owner(task, 0, &inode->i_uid, &inode->i_gid);
         security_task_to_inode(task, inode);
 
 out:
@@ -1715,7 +1760,6 @@ int pid_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
 {
         struct inode *inode = d_inode(dentry);
         struct task_struct *task;
-        const struct cred *cred;
         struct pid_namespace *pid = dentry->d_sb->s_fs_info;
 
         generic_fillattr(inode, stat);
@@ -1733,12 +1777,7 @@ int pid_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
                          */
                         return -ENOENT;
                 }
-                if ((inode->i_mode == (S_IFDIR|S_IRUGO|S_IXUGO)) ||
-                    task_dumpable(task)) {
-                        cred = __task_cred(task);
-                        stat->uid = cred->euid;
-                        stat->gid = cred->egid;
-                }
+                task_dump_owner(task, inode->i_mode, &stat->uid, &stat->gid);
         }
         rcu_read_unlock();
         return 0;
@@ -1754,18 +1793,11 @@ int pid_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
  * Rewrite the inode's ownerships here because the owning task may have
  * performed a setuid(), etc.
  *
- * Before the /proc/pid/status file was created the only way to read
- * the effective uid of a /process was to stat /proc/pid.  Reading
- * /proc/pid/status is slow enough that procps and other packages
- * kept stating /proc/pid.  To keep the rules in /proc simple I have
- * made this apply to all per process world readable and executable
- * directories.
  */
 int pid_revalidate(struct dentry *dentry, unsigned int flags)
 {
         struct inode *inode;
         struct task_struct *task;
-        const struct cred *cred;
 
         if (flags & LOOKUP_RCU)
                 return -ECHILD;
@@ -1774,17 +1806,8 @@ int pid_revalidate(struct dentry *dentry, unsigned int flags)
         task = get_proc_task(inode);
 
         if (task) {
-                if ((inode->i_mode == (S_IFDIR|S_IRUGO|S_IXUGO)) ||
-                    task_dumpable(task)) {
-                        rcu_read_lock();
-                        cred = __task_cred(task);
-                        inode->i_uid = cred->euid;
-                        inode->i_gid = cred->egid;
-                        rcu_read_unlock();
-                } else {
-                        inode->i_uid = GLOBAL_ROOT_UID;
-                        inode->i_gid = GLOBAL_ROOT_GID;
-                }
+                task_dump_owner(task, inode->i_mode, &inode->i_uid, &inode->i_gid);
+
                 inode->i_mode &= ~(S_ISUID | S_ISGID);
                 security_task_to_inode(task, inode);
                 put_task_struct(task);
@@ -1881,7 +1904,6 @@ static int map_files_d_revalidate(struct dentry *dentry, unsigned int flags)
         bool exact_vma_exists = false;
         struct mm_struct *mm = NULL;
         struct task_struct *task;
-        const struct cred *cred;
         struct inode *inode;
         int status = 0;
 
@@ -1906,16 +1928,8 @@ static int map_files_d_revalidate(struct dentry *dentry, unsigned int flags)
         mmput(mm);
 
         if (exact_vma_exists) {
-                if (task_dumpable(task)) {
-                        rcu_read_lock();
-                        cred = __task_cred(task);
-                        inode->i_uid = cred->euid;
-                        inode->i_gid = cred->egid;
-                        rcu_read_unlock();
-                } else {
-                        inode->i_uid = GLOBAL_ROOT_UID;
-                        inode->i_gid = GLOBAL_ROOT_GID;
-                }
+                task_dump_owner(task, 0, &inode->i_uid, &inode->i_gid);
+
                 security_task_to_inode(task, inode);
                 status = 1;
         }