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Subject[PATCH review 2/6] 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.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
kernel/user_namespace.c | 45 +++++++++++++++++++++++++++++++++++++++------
1 files changed, 39 insertions(+), 6 deletions(-)

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 24f8ec3..8b65083 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) &&
--
1.7.5.4


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