userns: Allow any uid or gid mappings that don't overlap.
Eric W. Biederman [Fri, 28 Dec 2012 06:27:29 +0000 (22:27 -0800)]
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>

kernel/user_namespace.c

index 24f8ec3..8b65083 100644 (file)
@@ -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) &&