Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 0bd14b4f authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

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: default avatarSerge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent c61a2810

kernel/user_namespace.c

+39 −6
Original line number Diff line number Diff line
@@ -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) &&