Re: [PATCH 2/2 v4] user namespaces: bump idmap limits to 340
From: Christian Brauner
Date: Sun Oct 22 2017 - 14:18:43 EST
On Thu, Oct 19, 2017 at 09:11:36PM +0200, Christian Brauner wrote:
> There are 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 4k
> kmalloc() which means we can have a maximum of 340 mappings
> (340 * size(struct uid_gid_extent) = 4080). For the latter case we use two
> pointers "forward" and "reverse". The forward pointer points to an array sorted
> by "first" and the reverse pointer 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 patches 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-NEW |
> |--------------|------------|-----------|
> | 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:
>
> #define __GNU_SOURCE
> #define __STDC_FORMAT_MACROS
> #include <errno.h>
> #include <dirent.h>
> #include <fcntl.h>
> #include <inttypes.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <unistd.h>
> #include <sys/stat.h>
> #include <sys/time.h>
> #include <sys/types.h>
>
> 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) {
> 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@xxxxxxxxxx>
> CC: Serge Hallyn <serge@xxxxxxxxxx>
> CC: Eric Biederman <ebiederm@xxxxxxxxxxxx>
> ---
> Changelog 2017-10-19:
> * kernel/user_namespace.c: Remove unnecessary mutex when freeing extents.
> * non-functional: Fix typos in commit message.
> * non-functional: Add headers to test program in commit message to make tests I
> performed easily reproducible.
> ---
> include/linux/user_namespace.h | 7 +-
> kernel/user_namespace.c | 355 +++++++++++++++++++++++++++++++++++++----
> 2 files changed, 329 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..c311249b7596 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 +183,18 @@ static void free_user_ns(struct work_struct *work)
> do {
> struct ucounts *ucounts = ns->ucounts;
> parent = ns->parent;
> + 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);
> + }
> retire_userns_sysctls(ns);
> #ifdef CONFIG_PERSISTENT_KEYRINGS
> key_put(ns->persistent_keyring_register);
> @@ -198,7 +212,84 @@ 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 +315,23 @@ 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 +354,23 @@ 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 +393,45 @@ 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 +702,15 @@ 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;
>
> - return extent;
> + if (map->nr_extents <= UID_GID_MAP_MAX_BASE_EXTENTS)
> + return &map->extent[pos];
> +
> + return &map->forward[pos];
> }
>
> static void *uid_m_start(struct seq_file *seq, loff_t *ppos)
> @@ -618,7 +782,10 @@ 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 +805,104 @@ 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);
This is wrong. kmemdup() does not return IS_ERR(). It returns NULL. So this
check must be adapted to:
if (!map->revers)
return -ENOMEM;
Sending a new version of the patch.
> + }
> +
> + /* 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 +913,7 @@ 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 +938,8 @@ 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 +967,7 @@ 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 +979,17 @@ 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 +999,33 @@ 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 +1036,26 @@ 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 +1063,34 @@ 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
>