userns: Allow any uid or gid mappings that don't overlap.

When I initially wrote the code for /proc/<pid>/uid_map.  I was lazy
and avoided duplicate mappings by the simple expedient of ensuring the
first number in a new extent was greater than any number in the
previous extent.

Unfortunately that precludes a number of valid mappings, and someone
noticed and complained.  So use a simple check to ensure that ranges
in the mapping extents don't overlap.

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

1 files changed, 39 insertions, 6 deletions

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 24f8ec3b64d8..8b650837083e 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -520,6 +520,42 @@ struct seq_operations proc_projid_seq_operations = {
         .show = projid_m_show,
 };
 
+static bool mappings_overlap(struct uid_gid_map *new_map, struct uid_gid_extent *extent)
+{
+        u32 upper_first, lower_first, upper_last, lower_last;
+        unsigned idx;
+
+        upper_first = extent->first;
+        lower_first = extent->lower_first;
+        upper_last = upper_first + extent->count - 1;
+        lower_last = lower_first + extent->count - 1;
+
+        for (idx = 0; idx < new_map->nr_extents; idx++) {
+                u32 prev_upper_first, prev_lower_first;
+                u32 prev_upper_last, prev_lower_last;
+                struct uid_gid_extent *prev;
+
+                prev = &new_map->extent[idx];
+
+                prev_upper_first = prev->first;
+                prev_lower_first = prev->lower_first;
+                prev_upper_last = prev_upper_first + prev->count - 1;
+                prev_lower_last = prev_lower_first + prev->count - 1;
+
+                /* Does the upper range intersect a previous extent? */
+                if ((prev_upper_first <= upper_last) &&
+                    (prev_upper_last >= upper_first))
+                        return true;
+
+                /* Does the lower range intersect a previous extent? */
+                if ((prev_lower_first <= lower_last) &&
+                    (prev_lower_last >= lower_first))
+                        return true;
+        }
+        return false;
+}
+
+
 static DEFINE_MUTEX(id_map_mutex);
 
 static ssize_t map_write(struct file *file, const char __user *buf,
@@ -532,7 +568,7 @@ static ssize_t map_write(struct file *file, const char __user *buf,
         struct user_namespace *ns = seq->private;
         struct uid_gid_map new_map;
         unsigned idx;
-        struct uid_gid_extent *extent, *last = NULL;
+        struct uid_gid_extent *extent = NULL;
         unsigned long page = 0;
         char *kbuf, *pos, *next_line;
         ssize_t ret = -EINVAL;
@@ -635,14 +671,11 @@ static ssize_t map_write(struct file *file, const char __user *buf,
                 if ((extent->lower_first + extent->count) <= extent->lower_first)
                         goto out;
 
-                /* For now only accept extents that are strictly in order */
-                if (last &&
-                    (((last->first + last->count) > extent->first) ||
-                     ((last->lower_first + last->count) > extent->lower_first)))
+                /* Do the ranges in extent overlap any previous extents? */
+                if (mappings_overlap(&new_map, extent))
                         goto out;
 
                 new_map.nr_extents++;
-                last = extent;
 
                 /* Fail if the file contains too many extents */
                 if ((new_map.nr_extents == UID_GID_MAP_MAX_EXTENTS) &&