[PATCH 2/2 v3] user namespaces: bump idmap limits to 340

Christian Brauner
2017-10-16T15:34:44Z

There a quite some use cases where users run into the current limit for {g,u}id
mappings. Consider a user requesting us to map everything but 999, and 1001 for
a given range of 1000000000 with a sub{g,u}id layout of:

some-user:100000:1000000000
some-user:999:1
some-user:1000:1
some-user:1001:1
some-user:1002:1

This translates to:

MAPPING-TYPE | CONTAINER | HOST | RANGE |
-------------|-----------|---------|-----------|
uid | 999 | 999 | 1 |
uid | 1001 | 1001 | 1 |
uid | 0 | 1000000 | 999 |
uid | 1000 | 1001000 | 1 |
uid | 1002 | 1001002 | 999998998 |
------------------------------------------------
gid | 999 | 999 | 1 |
gid | 1001 | 1001 | 1 |
gid | 0 | 1000000 | 999 |
gid | 1000 | 1001000 | 1 |
gid | 1002 | 1001002 | 999998998 |

which is already the current limit.

As discussed at LPC simply bumping the number of limits is not going to work
since this would mean that struct uid_gid_map won't fit into a single cache-line
anymore thereby regressing performance for the base-cases. The same problem
seems to arise when using a single pointer. So the idea is to use

struct uid_gid_extent {
u32 first;
u32 lower_first;
u32 count;
};

struct uid_gid_map { /* 64 bytes -- 1 cache line */
u32 nr_extents;
union {
struct uid_gid_extent extent[UID_GID_MAP_MAX_BASE_EXTENTS];
struct {
struct uid_gid_extent *forward;
struct uid_gid_extent *reverse;
};
};
};

For the base cases we will only use the struct uid_gid_extent extent member. If
we go over UID_GID_MAP_MAX_BASE_EXTENTS mappings we perform a single kalloc() of
4k which means we can have a maximum of 340 mappings
(340 * size(struct uid_gid_extent) = 4080). For the latter case we use two
pointer *forward, *reverse. The forward pointer points to an array sorted by
"first" and reverse points to an array sorted by "lower_first". We can then
perform binary search on those arrays.

Performance Testing:
When Eric introduced the extent-based struct uid_gid_map approach he measured
the performanc impact of his idmap changes:

> My benchmark consisted of going to single user mode where nothing else was
> running. On an ext4 filesystem opening 1,000,000 files and looping through all
> of the files 1000 times and calling fstat on the individuals files. This was
> to ensure I was benchmarking stat times where the inodes were in the kernels
> cache, but the inode values were not in the processors cache. My results:

> v3.4-rc1: ~= 156ns (unmodified v3.4-rc1 with user namespace support disabled)
> v3.4-rc1-userns-: ~= 155ns (v3.4-rc1 with my user namespace patches and user namespace support disabled)
> v3.4-rc1-userns+: ~= 164ns (v3.4-rc1 with my user namespace patches and user namespace support enabled)

I used an identical approach on my laptop. Here's a thorough description of what
I did. I built a 4.14.0-rc4 mainline kernel with my new idmap patch applied. I
booted into single user mode and used an ext4 filesystem to open/create
1,000,000 files. Then I looped through all of the files calling fstat() on each
of them 1000 times and calculated the mean fstat() time for a single file. (The
test program can be found below.)

Here are the results. For fun, I compared the first version of my patch which
scaled linearly with the new version of the patch:

| # MAPPINGS | PATCH-V1 | PATCH-V2 |
|--------------|------------|----------|
| 0 mappings | 158 ns | 158 ns |
| 1 mappings | 164 ns | 157 ns |
| 2 mappings | 170 ns | 158 ns |
| 3 mappings | 175 ns | 161 ns |
| 5 mappings | 187 ns | 165 ns |
| 10 mappings | 218 ns | 199 ns |
| 50 mappings | 528 ns | 218 ns |
| 100 mappings | 980 ns | 229 ns |
| 200 mappings | 1880 ns | 239 ns |
| 300 mappings | 2760 ns | 240 ns |
| 340 mappings | not tested | 248 ns |

Here's the test program I used. I asked Eric what he did and this is a more
"advanced" implementation of the idea. It's pretty straight-forward:

int main(int argc, char *argv[])
{
int ret;
size_t i, k;
int fd[1000000];
int times[1000];
char pathname[4096];
struct stat st;
struct timeval t1, t2;
uint64_t time_in_mcs;
uint64_t sum = 0;

if (argc != 2) {
fprintf(stderr, "Please specify a directory where to create "
"the test files\n");
exit(EXIT_FAILURE);
}

for (i = 0; i < sizeof(fd) / sizeof(fd[0]); i++) {
sprintf(pathname, "%s/idmap_test_%zu", argv[1], i);
fd[i]= open(pathname, O_RDWR | O_CREAT, S_IXUSR | S_IXGRP | S_IXOTH);
if (fd[i] < 0) {
printf("asdf: %s\n", strerror(errno));
ssize_t j;
for (j = i; j >= 0; j--)
close(fd[j]);
exit(EXIT_FAILURE);
}
}

for (k = 0; k < 1000; k++) {
ret = gettimeofday(&t1, NULL);
if (ret < 0)
goto close_all;

for (i = 0; i < sizeof(fd) / sizeof(fd[0]); i++) {
ret = fstat(fd[i], &st);
if (ret < 0)
goto close_all;
}

ret = gettimeofday(&t2, NULL);
if (ret < 0)
goto close_all;

time_in_mcs = (1000000 * t2.tv_sec + t2.tv_usec) -
(1000000 * t1.tv_sec + t1.tv_usec);
printf("Total time in micro seconds: %" PRIu64 "\n",
time_in_mcs);
printf("Total time in nanoseconds: %" PRIu64 "\n",
time_in_mcs * 1000);
printf("Time per file in nanoseconds: %" PRIu64 "\n",
(time_in_mcs * 1000) / 1000000);
times[k] = (time_in_mcs * 1000) / 1000000;
}

close_all:
for (i = 0; i < sizeof(fd) / sizeof(fd[0]); i++)
close(fd[i]);

if (ret < 0)
exit(EXIT_FAILURE);

for (k = 0; k < 1000; k++) {
sum += times[k];
}

printf("Mean time per file in nanoseconds: %" PRIu64 "\n", sum / 1000);

exit(EXIT_SUCCESS);;
}

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
CC: Serge Hallyn <serge@hallyn.com>
CC: Eric Biederman <ebiederm@xmission.com>

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
include/linux/user_namespace.h | 7 +-
kernel/user_namespace.c | 359 +++++++++++++++++++++++++++++++++++++----
2 files changed, 333 insertions(+), 33 deletions(-)

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 7c83d7f6289b..1c1046a60fb4 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -10,7 +10,8 @@
#include <linux/sysctl.h>
#include <linux/err.h>

-#define UID_GID_MAP_MAX_EXTENTS 5
+#define UID_GID_MAP_MAX_BASE_EXTENTS 5
+#define UID_GID_MAP_MAX_EXTENTS 340

struct uid_gid_extent {
u32 first;
@@ -18,10 +19,10 @@ struct uid_gid_extent {
u32 count;
};

-struct uid_gid_map { /* 64 bytes -- 1 cache line */
+struct uid_gid_map { /* 64 bytes -- 1 cache line */
u32 nr_extents;
union {
- struct uid_gid_extent extent[UID_GID_MAP_MAX_EXTENTS];
+ struct uid_gid_extent extent[UID_GID_MAP_MAX_BASE_EXTENTS];
struct {
struct uid_gid_extent *forward;
struct uid_gid_extent *reverse;
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index c490f1e4313b..eceb03ae597c 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -23,6 +23,8 @@
#include <linux/ctype.h>
#include <linux/projid.h>
#include <linux/fs_struct.h>
+#include <linux/bsearch.h>
+#include <linux/sort.h>

static struct kmem_cache *user_ns_cachep __read_mostly;
static DEFINE_MUTEX(userns_state_mutex);
@@ -181,6 +183,22 @@ static void free_user_ns(struct work_struct *work)
do {
struct ucounts *ucounts = ns->ucounts;
parent = ns->parent;
+
+ mutex_lock(&userns_state_mutex);
+ if (ns->gid_map.nr_extents > UID_GID_MAP_MAX_BASE_EXTENTS) {
+ kfree(ns->gid_map.forward);
+ kfree(ns->gid_map.reverse);
+ }
+ if (ns->uid_map.nr_extents > UID_GID_MAP_MAX_BASE_EXTENTS) {
+ kfree(ns->uid_map.forward);
+ kfree(ns->uid_map.reverse);
+ }
+ if (ns->projid_map.nr_extents > UID_GID_MAP_MAX_BASE_EXTENTS) {
+ kfree(ns->projid_map.forward);
+ kfree(ns->projid_map.reverse);
+ }
+ mutex_unlock(&userns_state_mutex);
+
retire_userns_sysctls(ns);
#ifdef CONFIG_PERSISTENT_KEYRINGS
key_put(ns->persistent_keyring_register);
@@ -198,7 +216,84 @@ void __put_user_ns(struct user_namespace *ns)
}
EXPORT_SYMBOL(__put_user_ns);

-static u32 map_id_range_down(struct uid_gid_map *map, u32 id, u32 count)
+/**
+ * idmap_key struct holds the information necessary to find an idmapping in a
+ * sorted idmap array. It is passed to cmp_map_id() as first argument.
+ */
+struct idmap_key {
+ bool map_up; /* true -> id from kid; false -> kid from id */
+ u32 id; /* id to find */
+ u32 count; /* == 0 unless used with map_id_range_down() */
+};
+
+/**
+ * cmp_map_id - Function to be passed to bsearch() to find the requested
+ * idmapping. Expects struct idmap_key to be passed via @k.
+ */
+static int cmp_map_id(const void *k, const void *e)
+{
+ u32 first, last, id2;
+ const struct idmap_key *key = k;
+ const struct uid_gid_extent *el = e;
+
+ /* handle map_id_range_down() */
+ if (key->count)
+ id2 = key->id + key->count - 1;
+ else
+ id2 = key->id;
+
+ /* handle map_id_{down,up}() */
+ if (key->map_up)
+ first = el->lower_first;
+ else
+ first = el->first;
+
+ last = first + el->count - 1;
+
+ if (key->id >= first && key->id <= last &&
+ (id2 >= first && id2 <= last))
+ return 0;
+
+ if (key->id < first || id2 < first)
+ return -1;
+
+ return 1;
+}
+
+/**
+ * map_id_range_down_max - Find idmap via binary search in ordered idmap array.
+ * Can only be called if number of mappings exceeds UID_GID_MAP_MAX_BASE_EXTENTS.
+ */
+static u32 map_id_range_down_max(struct uid_gid_map *map, u32 id, u32 count)
+{
+ u32 extents;
+ struct uid_gid_extent *extent;
+ struct idmap_key key;
+
+ key.map_up = false;
+ key.count = count;
+ key.id = id;
+
+ extents = map->nr_extents;
+ smp_rmb();
+
+ extent = bsearch(&key, map->forward, extents,
+ sizeof(struct uid_gid_extent), cmp_map_id);
+ /* Map the id or note failure */
+ if (extent)
+ id = (id - extent->first) + extent->lower_first;
+ else
+ id = (u32) -1;
+
+ return id;
+}
+
+/**
+ * map_id_range_down_base - Find idmap via binary search in static extent array.
+ * Can only be called if number of mappings is equal or less than
+ * UID_GID_MAP_MAX_BASE_EXTENTS.
+ */
+static u32 map_id_range_down_base(struct uid_gid_map *map, u32 id, u32 count)
{
unsigned idx, extents;
u32 first, last, id2;
@@ -224,7 +319,23 @@ static u32 map_id_range_down(struct uid_gid_map *map, u32 id, u32 count)
return id;
}

-static u32 map_id_down(struct uid_gid_map *map, u32 id)
+static u32 map_id_range_down(struct uid_gid_map *map, u32 id, u32 count)
+{
+ u32 extents = map->nr_extents;
+ smp_rmb();
+
+ if (extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
+ return map_id_range_down_base(map, id, count);
+
+ return map_id_range_down_max(map, id, count);
+}
+
+/**
+ * map_id_down_base - Find idmap via binary search in static extent array.
+ * Can only be called if number of mappings is equal or less than
+ * UID_GID_MAP_MAX_BASE_EXTENTS.
+ */
+static u32 map_id_down_base(struct uid_gid_map *map, u32 id)
{
unsigned idx, extents;
u32 first, last;
@@ -247,7 +358,23 @@ static u32 map_id_down(struct uid_gid_map *map, u32 id)
return id;
}

-static u32 map_id_up(struct uid_gid_map *map, u32 id)
+static u32 map_id_down(struct uid_gid_map *map, u32 id)
+{
+ u32 extents = map->nr_extents;
+ smp_rmb();
+
+ if (extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
+ return map_id_down_base(map, id);
+
+ return map_id_range_down_max(map, id, 0);
+}
+
+/**
+ * map_id_up_base - Find idmap via binary search in static extent array.
+ * Can only be called if number of mappings is equal or less than
+ * UID_GID_MAP_MAX_BASE_EXTENTS.
+ */
+static u32 map_id_up_base(struct uid_gid_map *map, u32 id)
{
unsigned idx, extents;
u32 first, last;
@@ -270,6 +397,45 @@ static u32 map_id_up(struct uid_gid_map *map, u32 id)
return id;
}

+/**
+ * map_id_up_max - Find idmap via binary search in ordered idmap array.
+ * Can only be called if number of mappings exceeds UID_GID_MAP_MAX_BASE_EXTENTS.
+ */
+static u32 map_id_up_max(struct uid_gid_map *map, u32 id)
+{
+ u32 extents;
+ struct uid_gid_extent *extent;
+ struct idmap_key key;
+
+ key.map_up = true;
+ key.count = 0;
+ key.id = id;
+
+ extents = map->nr_extents;
+ smp_rmb();
+
+ extent = bsearch(&key, map->reverse, extents,
+ sizeof(struct uid_gid_extent), cmp_map_id);
+ /* Map the id or note failure */
+ if (extent)
+ id = (id - extent->lower_first) + extent->first;
+ else
+ id = (u32) -1;
+
+ return id;
+}
+
+static u32 map_id_up(struct uid_gid_map *map, u32 id)
+{
+ u32 extents = map->nr_extents;
+ smp_rmb();
+
+ if (extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
+ return map_id_up_base(map, id);
+
+ return map_id_up_max(map, id);
+}
+
/**
* make_kuid - Map a user-namespace uid pair into a kuid.
* @ns: User namespace that the uid is in
@@ -540,13 +706,15 @@ static int projid_m_show(struct seq_file *seq, void *v)
static void *m_start(struct seq_file *seq, loff_t *ppos,
struct uid_gid_map *map)
{
- struct uid_gid_extent *extent = NULL;
loff_t pos = *ppos;

- if (pos < map->nr_extents)
- extent = &map->extent[pos];
+ if (pos >= map->nr_extents)
+ return NULL;
+
+ if (map->nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
+ return &map->extent[pos];

- return extent;
+ return &map->forward[pos];
}

static void *uid_m_start(struct seq_file *seq, loff_t *ppos)
@@ -618,7 +786,10 @@ static bool mappings_overlap(struct uid_gid_map *new_map,
u32 prev_upper_last, prev_lower_last;
struct uid_gid_extent *prev;

- prev = &new_map->extent[idx];
+ if (new_map->nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
+ prev = &new_map->extent[idx];
+ else
+ prev = &new_map->forward[idx];

prev_upper_first = prev->first;
prev_lower_first = prev->lower_first;
@@ -638,6 +809,104 @@ static bool mappings_overlap(struct uid_gid_map *new_map,
return false;
}

+/**
+ * insert_extent - Safely insert a new idmap extent into struct uid_gid_map.
+ * Takes care to allocate a 4K block of memory if the number of mappings exceeds
+ * UID_GID_MAP_MAX_BASE_EXTENTS.
+ */
+static int insert_extent(struct uid_gid_map *map, struct uid_gid_extent *extent)
+{
+ if (map->nr_extents < UID_GID_MAP_MAX_BASE_EXTENTS) {
+ map->extent[map->nr_extents].first = extent->first;
+ map->extent[map->nr_extents].lower_first = extent->lower_first;
+ map->extent[map->nr_extents].count = extent->count;
+ return 0;
+ }
+
+ if (map->nr_extents == UID_GID_MAP_MAX_BASE_EXTENTS) {
+ struct uid_gid_extent *forward;
+
+ /* Allocate memory for 340 mappings. */
+ forward = kmalloc(sizeof(struct uid_gid_extent) *
+ UID_GID_MAP_MAX_EXTENTS, GFP_KERNEL);
+ if (IS_ERR(forward))
+ return PTR_ERR(forward);
+
+ /* Copy over memory. Only set up memory for the forward pointer.
+ * Defer the memory setup for the reverse pointer.
+ */
+ memcpy(forward, map->extent,
+ map->nr_extents * sizeof(map->extent[0]));
+
+ map->forward = forward;
+ map->reverse = NULL;
+ }
+
+ map->forward[map->nr_extents].first = extent->first;
+ map->forward[map->nr_extents].lower_first = extent->lower_first;
+ map->forward[map->nr_extents].count = extent->count;
+ return 0;
+}
+
+/* cmp function to sort() forward mappings */
+static int cmp_extents_forward(const void *a, const void *b)
+{
+ const struct uid_gid_extent *e1 = a;
+ const struct uid_gid_extent *e2 = b;
+
+ if (e1->first < e2->first)
+ return -1;
+
+ if (e1->first > e2->first)
+ return 1;
+
+ return 0;
+}
+
+/* cmp function to sort() reverse mappings */
+static int cmp_extents_reverse(const void *a, const void *b)
+{
+ const struct uid_gid_extent *e1 = a;
+ const struct uid_gid_extent *e2 = b;
+
+ if (e1->lower_first < e2->lower_first)
+ return -1;
+
+ if (e1->lower_first > e2->lower_first)
+ return 1;
+
+ return 0;
+}
+
+/**
+ * sort_idmaps - Sorts an array of idmap entries.
+ * Can only be called if number of mappings exceeds UID_GID_MAP_MAX_BASE_EXTENTS.
+ */
+static int sort_idmaps(struct uid_gid_map *map)
+{
+ if (map->nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
+ return 0;
+
+ /* Sort forward array. */
+ sort(map->forward, map->nr_extents, sizeof(struct uid_gid_extent),
+ cmp_extents_forward, NULL);
+
+ /* Only copy the memory from forward we actually need. */
+ map->reverse = kmemdup(map->forward,
+ map->nr_extents * sizeof(struct uid_gid_extent),
+ GFP_KERNEL);
+ if (IS_ERR(map->reverse)) {
+ map->reverse = NULL;
+ return PTR_ERR(map->reverse);
+ }
+
+ /* Sort reverse array. */
+ sort(map->reverse, map->nr_extents, sizeof(struct uid_gid_extent),
+ cmp_extents_reverse, NULL);
+
+ return 0;
+}
+
static ssize_t map_write(struct file *file, const char __user *buf,
size_t count, loff_t *ppos,
int cap_setid,
@@ -648,7 +917,7 @@ 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 = NULL;
+ struct uid_gid_extent extent;
char *kbuf = NULL, *pos, *next_line;
ssize_t ret = -EINVAL;

@@ -673,6 +942,8 @@ static ssize_t map_write(struct file *file, const char __user *buf,
*/
mutex_lock(&userns_state_mutex);

+ memset(&new_map, 0, sizeof(struct uid_gid_map));
+
ret = -EPERM;
/* Only allow one successful write to the map */
if (map->nr_extents != 0)
@@ -700,9 +971,7 @@ static ssize_t map_write(struct file *file, const char __user *buf,
/* Parse the user data */
ret = -EINVAL;
pos = kbuf;
- new_map.nr_extents = 0;
for (; pos; pos = next_line) {
- extent = &new_map.extent[new_map.nr_extents];

/* Find the end of line and ensure I don't look past it */
next_line = strchr(pos, '\n');
@@ -714,17 +983,17 @@ static ssize_t map_write(struct file *file, const char __user *buf,
}

pos = skip_spaces(pos);
- extent->first = simple_strtoul(pos, &pos, 10);
+ extent.first = simple_strtoul(pos, &pos, 10);
if (!isspace(*pos))
goto out;

pos = skip_spaces(pos);
- extent->lower_first = simple_strtoul(pos, &pos, 10);
+ extent.lower_first = simple_strtoul(pos, &pos, 10);
if (!isspace(*pos))
goto out;

pos = skip_spaces(pos);
- extent->count = simple_strtoul(pos, &pos, 10);
+ extent.count = simple_strtoul(pos, &pos, 10);
if (*pos && !isspace(*pos))
goto out;

@@ -734,29 +1003,33 @@ static ssize_t map_write(struct file *file, const char __user *buf,
goto out;

/* Verify we have been given valid starting values */
- if ((extent->first == (u32) -1) ||
- (extent->lower_first == (u32) -1))
+ if ((extent.first == (u32) -1) ||
+ (extent.lower_first == (u32) -1))
goto out;

/* Verify count is not zero and does not cause the
* extent to wrap
*/
- if ((extent->first + extent->count) <= extent->first)
+ if ((extent.first + extent.count) <= extent.first)
goto out;
- if ((extent->lower_first + extent->count) <=
- extent->lower_first)
+ if ((extent.lower_first + extent.count) <=
+ extent.lower_first)
goto out;

/* Do the ranges in extent overlap any previous extents? */
- if (mappings_overlap(&new_map, extent))
+ if (mappings_overlap(&new_map, &extent))
goto out;

- new_map.nr_extents++;
-
- /* Fail if the file contains too many extents */
- if ((new_map.nr_extents == UID_GID_MAP_MAX_EXTENTS) &&
+ if ((new_map.nr_extents + 1) == UID_GID_MAP_MAX_EXTENTS &&
(next_line != NULL))
goto out;
+
+ ret = insert_extent(&new_map, &extent);
+ if (ret < 0)
+ goto out;
+ ret = -EINVAL;
+
+ new_map.nr_extents++;
}
/* Be very certaint the new map actually exists */
if (new_map.nr_extents == 0)
@@ -767,16 +1040,26 @@ static ssize_t map_write(struct file *file, const char __user *buf,
if (!new_idmap_permitted(file, ns, cap_setid, &new_map))
goto out;

+ ret = sort_idmaps(&new_map);
+ if (ret < 0)
+ goto out;
+
+ ret = -EPERM;
/* Map the lower ids from the parent user namespace to the
* kernel global id space.
*/
for (idx = 0; idx < new_map.nr_extents; idx++) {
+ struct uid_gid_extent *e;
u32 lower_first;
- extent = &new_map.extent[idx];
+
+ if (new_map.nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
+ e = &new_map.extent[idx];
+ else
+ e = &new_map.forward[idx];

lower_first = map_id_range_down(parent_map,
- extent->lower_first,
- extent->count);
+ e->lower_first,
+ e->count);

/* Fail if we can not map the specified extent to
* the kernel global id space.
@@ -784,18 +1067,34 @@ static ssize_t map_write(struct file *file, const char __user *buf,
if (lower_first == (u32) -1)
goto out;

- extent->lower_first = lower_first;
+ e->lower_first = lower_first;
}

/* Install the map */
- memcpy(map->extent, new_map.extent,
- new_map.nr_extents*sizeof(new_map.extent[0]));
+ if (new_map.nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS) {
+ memcpy(map->extent, new_map.extent,
+ new_map.nr_extents * sizeof(new_map.extent[0]));
+ } else {
+ map->forward = new_map.forward;
+ map->reverse = new_map.reverse;
+ }
smp_wmb();
map->nr_extents = new_map.nr_extents;

*ppos = count;
ret = count;
out:
+ if (ret < 0 && new_map.nr_extents > UID_GID_MAP_MAX_BASE_EXTENTS) {
+ if (new_map.forward)
+ kfree(new_map.forward);
+ map->forward = NULL;
+
+ if (new_map.reverse)
+ kfree(new_map.reverse);
+ map->reverse = NULL;
+ map->nr_extents = 0;
+ }
+
mutex_unlock(&userns_state_mutex);
kfree(kbuf);
return ret;
--
2.14.1