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linux-next/kernel/groups.c
Alexey Dobriyan 81243eacfa cred: simpler, 1D supplementary groups
Current supplementary groups code can massively overallocate memory and
is implemented in a way so that access to individual gid is done via 2D
array.

If number of gids is <= 32, memory allocation is more or less tolerable
(140/148 bytes).  But if it is not, code allocates full page (!)
regardless and, what's even more fun, doesn't reuse small 32-entry
array.

2D array means dependent shifts, loads and LEAs without possibility to
optimize them (gid is never known at compile time).

All of the above is unnecessary.  Switch to the usual
trailing-zero-len-array scheme.  Memory is allocated with
kmalloc/vmalloc() and only as much as needed.  Accesses become simpler
(LEA 8(gi,idx,4) or even without displacement).

Maximum number of gids is 65536 which translates to 256KB+8 bytes.  I
think kernel can handle such allocation.

On my usual desktop system with whole 9 (nine) aux groups, struct
group_info shrinks from 148 bytes to 44 bytes, yay!

Nice side effects:

 - "gi->gid[i]" is shorter than "GROUP_AT(gi, i)", less typing,

 - fix little mess in net/ipv4/ping.c
   should have been using GROUP_AT macro but this point becomes moot,

 - aux group allocation is persistent and should be accounted as such.

Link: http://lkml.kernel.org/r/20160817201927.GA2096@p183.telecom.by
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Vasily Kulikov <segoon@openwall.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-10-07 18:46:30 -07:00

253 lines
5.2 KiB
C

/*
* Supplementary group IDs
*/
#include <linux/cred.h>
#include <linux/export.h>
#include <linux/slab.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/user_namespace.h>
#include <linux/vmalloc.h>
#include <asm/uaccess.h>
struct group_info *groups_alloc(int gidsetsize)
{
struct group_info *gi;
unsigned int len;
len = sizeof(struct group_info) + sizeof(kgid_t) * gidsetsize;
gi = kmalloc(len, GFP_KERNEL_ACCOUNT|__GFP_NOWARN|__GFP_NORETRY);
if (!gi)
gi = __vmalloc(len, GFP_KERNEL_ACCOUNT|__GFP_HIGHMEM, PAGE_KERNEL);
if (!gi)
return NULL;
atomic_set(&gi->usage, 1);
gi->ngroups = gidsetsize;
return gi;
}
EXPORT_SYMBOL(groups_alloc);
void groups_free(struct group_info *group_info)
{
kvfree(group_info);
}
EXPORT_SYMBOL(groups_free);
/* export the group_info to a user-space array */
static int groups_to_user(gid_t __user *grouplist,
const struct group_info *group_info)
{
struct user_namespace *user_ns = current_user_ns();
int i;
unsigned int count = group_info->ngroups;
for (i = 0; i < count; i++) {
gid_t gid;
gid = from_kgid_munged(user_ns, group_info->gid[i]);
if (put_user(gid, grouplist+i))
return -EFAULT;
}
return 0;
}
/* fill a group_info from a user-space array - it must be allocated already */
static int groups_from_user(struct group_info *group_info,
gid_t __user *grouplist)
{
struct user_namespace *user_ns = current_user_ns();
int i;
unsigned int count = group_info->ngroups;
for (i = 0; i < count; i++) {
gid_t gid;
kgid_t kgid;
if (get_user(gid, grouplist+i))
return -EFAULT;
kgid = make_kgid(user_ns, gid);
if (!gid_valid(kgid))
return -EINVAL;
group_info->gid[i] = kgid;
}
return 0;
}
/* a simple Shell sort */
static void groups_sort(struct group_info *group_info)
{
int base, max, stride;
int gidsetsize = group_info->ngroups;
for (stride = 1; stride < gidsetsize; stride = 3 * stride + 1)
; /* nothing */
stride /= 3;
while (stride) {
max = gidsetsize - stride;
for (base = 0; base < max; base++) {
int left = base;
int right = left + stride;
kgid_t tmp = group_info->gid[right];
while (left >= 0 && gid_gt(group_info->gid[left], tmp)) {
group_info->gid[right] = group_info->gid[left];
right = left;
left -= stride;
}
group_info->gid[right] = tmp;
}
stride /= 3;
}
}
/* a simple bsearch */
int groups_search(const struct group_info *group_info, kgid_t grp)
{
unsigned int left, right;
if (!group_info)
return 0;
left = 0;
right = group_info->ngroups;
while (left < right) {
unsigned int mid = (left+right)/2;
if (gid_gt(grp, group_info->gid[mid]))
left = mid + 1;
else if (gid_lt(grp, group_info->gid[mid]))
right = mid;
else
return 1;
}
return 0;
}
/**
* set_groups - Change a group subscription in a set of credentials
* @new: The newly prepared set of credentials to alter
* @group_info: The group list to install
*/
void set_groups(struct cred *new, struct group_info *group_info)
{
put_group_info(new->group_info);
groups_sort(group_info);
get_group_info(group_info);
new->group_info = group_info;
}
EXPORT_SYMBOL(set_groups);
/**
* set_current_groups - Change current's group subscription
* @group_info: The group list to impose
*
* Validate a group subscription and, if valid, impose it upon current's task
* security record.
*/
int set_current_groups(struct group_info *group_info)
{
struct cred *new;
new = prepare_creds();
if (!new)
return -ENOMEM;
set_groups(new, group_info);
return commit_creds(new);
}
EXPORT_SYMBOL(set_current_groups);
SYSCALL_DEFINE2(getgroups, int, gidsetsize, gid_t __user *, grouplist)
{
const struct cred *cred = current_cred();
int i;
if (gidsetsize < 0)
return -EINVAL;
/* no need to grab task_lock here; it cannot change */
i = cred->group_info->ngroups;
if (gidsetsize) {
if (i > gidsetsize) {
i = -EINVAL;
goto out;
}
if (groups_to_user(grouplist, cred->group_info)) {
i = -EFAULT;
goto out;
}
}
out:
return i;
}
bool may_setgroups(void)
{
struct user_namespace *user_ns = current_user_ns();
return ns_capable(user_ns, CAP_SETGID) &&
userns_may_setgroups(user_ns);
}
/*
* SMP: Our groups are copy-on-write. We can set them safely
* without another task interfering.
*/
SYSCALL_DEFINE2(setgroups, int, gidsetsize, gid_t __user *, grouplist)
{
struct group_info *group_info;
int retval;
if (!may_setgroups())
return -EPERM;
if ((unsigned)gidsetsize > NGROUPS_MAX)
return -EINVAL;
group_info = groups_alloc(gidsetsize);
if (!group_info)
return -ENOMEM;
retval = groups_from_user(group_info, grouplist);
if (retval) {
put_group_info(group_info);
return retval;
}
retval = set_current_groups(group_info);
put_group_info(group_info);
return retval;
}
/*
* Check whether we're fsgid/egid or in the supplemental group..
*/
int in_group_p(kgid_t grp)
{
const struct cred *cred = current_cred();
int retval = 1;
if (!gid_eq(grp, cred->fsgid))
retval = groups_search(cred->group_info, grp);
return retval;
}
EXPORT_SYMBOL(in_group_p);
int in_egroup_p(kgid_t grp)
{
const struct cred *cred = current_cred();
int retval = 1;
if (!gid_eq(grp, cred->egid))
retval = groups_search(cred->group_info, grp);
return retval;
}
EXPORT_SYMBOL(in_egroup_p);