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Add a reference to ucounts for each cred

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[ Upstream commit 905ae01c4ae2ae3df05bb141801b1db4b7d83c61 ]

For RLIMIT_NPROC and some other rlimits the user_struct that holds the
global limit is kept alive for the lifetime of a process by keeping it
in struct cred. Adding a pointer to ucounts in the struct cred will
allow to track RLIMIT_NPROC not only for user in the system, but for
user in the user_namespace.

Updating ucounts may require memory allocation which may fail. So, we
cannot change cred.ucounts in the commit_creds() because this function
cannot fail and it should always return 0. For this reason, we modify
cred.ucounts before calling the commit_creds().

Changelog

v6:
* Fix null-ptr-deref in is_ucounts_overlimit() detected by trinity. This
  error was caused by the fact that cred_alloc_blank() left the ucounts
  pointer empty.

Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Alexey Gladkov <legion@kernel.org>
Link: https://lkml.kernel.org/r/b37aaef28d8b9b0d757e07ba6dd27281bbe39259.1619094428.git.legion@kernel.org
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Alexey Gladkov 2021-04-22 14:27:09 +02:00 committed by Greg Kroah-Hartman
parent 61a7a634a0
commit b2c4d9a33c
8 changed files with 108 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
fs/exec.c
View File

@ -1347,6 +1347,10 @@ int begin_new_exec(struct linux_binprm * bprm)
WRITE_ONCE(me->self_exec_id, me->self_exec_id + 1);
flush_signal_handlers(me, 0);
retval = set_cred_ucounts(bprm->cred);
if (retval < 0)
goto out_unlock;
/*
* install the new credentials for this executable
*/

2
include/linux/cred.h
View File

@ -144,6 +144,7 @@ struct cred {
#endif
struct user_struct *user; /* real user ID subscription */
struct user_namespace *user_ns; /* user_ns the caps and keyrings are relative to. */
struct ucounts *ucounts;
struct group_info *group_info; /* supplementary groups for euid/fsgid */
/* RCU deletion */
union {
@ -170,6 +171,7 @@ extern int set_security_override_from_ctx(struct cred *, const char *);
extern int set_create_files_as(struct cred *, struct inode *);
extern int cred_fscmp(const struct cred *, const struct cred *);
extern void __init cred_init(void);
extern int set_cred_ucounts(struct cred *);
/*
* check for validity of credentials

4
include/linux/user_namespace.h
View File

@ -101,11 +101,15 @@ struct ucounts {
};
extern struct user_namespace init_user_ns;
extern struct ucounts init_ucounts;
bool setup_userns_sysctls(struct user_namespace *ns);
void retire_userns_sysctls(struct user_namespace *ns);
struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, enum ucount_type type);
void dec_ucount(struct ucounts *ucounts, enum ucount_type type);
struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid);
struct ucounts *get_ucounts(struct ucounts *ucounts);
void put_ucounts(struct ucounts *ucounts);
#ifdef CONFIG_USER_NS

40
kernel/cred.c
View File

@ -60,6 +60,7 @@ struct cred init_cred = {
.user = INIT_USER,
.user_ns = &init_user_ns,
.group_info = &init_groups,
.ucounts = &init_ucounts,
};
static inline void set_cred_subscribers(struct cred *cred, int n)
@ -119,6 +120,8 @@ static void put_cred_rcu(struct rcu_head *rcu)
if (cred->group_info)
put_group_info(cred->group_info);
free_uid(cred->user);
if (cred->ucounts)
put_ucounts(cred->ucounts);
put_user_ns(cred->user_ns);
kmem_cache_free(cred_jar, cred);
}
@ -222,6 +225,7 @@ struct cred *cred_alloc_blank(void)
#ifdef CONFIG_DEBUG_CREDENTIALS
new->magic = CRED_MAGIC;
#endif
new->ucounts = get_ucounts(&init_ucounts);
if (security_cred_alloc_blank(new, GFP_KERNEL_ACCOUNT) < 0)
goto error;
@ -284,6 +288,11 @@ struct cred *prepare_creds(void)
if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
goto error;
new->ucounts = get_ucounts(new->ucounts);
if (!new->ucounts)
goto error;
validate_creds(new);
return new;
@ -363,6 +372,8 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
ret = create_user_ns(new);
if (ret < 0)
goto error_put;
if (set_cred_ucounts(new) < 0)
goto error_put;
}
#ifdef CONFIG_KEYS
@ -653,6 +664,31 @@ int cred_fscmp(const struct cred *a, const struct cred *b)
}
EXPORT_SYMBOL(cred_fscmp);
int set_cred_ucounts(struct cred *new)
{
struct task_struct *task = current;
const struct cred *old = task->real_cred;
struct ucounts *old_ucounts = new->ucounts;
if (new->user == old->user && new->user_ns == old->user_ns)
return 0;
/*
* This optimization is needed because alloc_ucounts() uses locks
* for table lookups.
*/
if (old_ucounts && old_ucounts->ns == new->user_ns && uid_eq(old_ucounts->uid, new->euid))
return 0;
if (!(new->ucounts = alloc_ucounts(new->user_ns, new->euid)))
return -EAGAIN;
if (old_ucounts)
put_ucounts(old_ucounts);
return 0;
}
/*
* initialise the credentials stuff
*/
@ -719,6 +755,10 @@ struct cred *prepare_kernel_cred(struct task_struct *daemon)
if (security_prepare_creds(new, old, GFP_KERNEL_ACCOUNT) < 0)
goto error;
new->ucounts = get_ucounts(new->ucounts);
if (!new->ucounts)
goto error;
put_cred(old);
validate_creds(new);
return new;

6
kernel/fork.c
View File

@ -2960,6 +2960,12 @@ int ksys_unshare(unsigned long unshare_flags)
if (err)
goto bad_unshare_cleanup_cred;
if (new_cred) {
err = set_cred_ucounts(new_cred);
if (err)
goto bad_unshare_cleanup_cred;
}
if (new_fs || new_fd || do_sysvsem || new_cred || new_nsproxy) {
if (do_sysvsem) {
/*

12
kernel/sys.c
View File

@ -552,6 +552,10 @@ long __sys_setreuid(uid_t ruid, uid_t euid)
if (retval < 0)
goto error;
retval = set_cred_ucounts(new);
if (retval < 0)
goto error;
return commit_creds(new);
error:
@ -610,6 +614,10 @@ long __sys_setuid(uid_t uid)
if (retval < 0)
goto error;
retval = set_cred_ucounts(new);
if (retval < 0)
goto error;
return commit_creds(new);
error:
@ -685,6 +693,10 @@ long __sys_setresuid(uid_t ruid, uid_t euid, uid_t suid)
if (retval < 0)
goto error;
retval = set_cred_ucounts(new);
if (retval < 0)
goto error;
return commit_creds(new);
error:

40
kernel/ucount.c
View File

@ -8,6 +8,12 @@
#include <linux/kmemleak.h>
#include <linux/user_namespace.h>
struct ucounts init_ucounts = {
.ns = &init_user_ns,
.uid = GLOBAL_ROOT_UID,
.count = 1,
};
#define UCOUNTS_HASHTABLE_BITS 10
static struct hlist_head ucounts_hashtable[(1 << UCOUNTS_HASHTABLE_BITS)];
static DEFINE_SPINLOCK(ucounts_lock);
@ -125,7 +131,15 @@ static struct ucounts *find_ucounts(struct user_namespace *ns, kuid_t uid, struc
return NULL;
}
static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
static void hlist_add_ucounts(struct ucounts *ucounts)
{
struct hlist_head *hashent = ucounts_hashentry(ucounts->ns, ucounts->uid);
spin_lock_irq(&ucounts_lock);
hlist_add_head(&ucounts->node, hashent);
spin_unlock_irq(&ucounts_lock);
}
struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
{
struct hlist_head *hashent = ucounts_hashentry(ns, uid);
struct ucounts *ucounts, *new;
@ -160,7 +174,26 @@ static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
return ucounts;
}
static void put_ucounts(struct ucounts *ucounts)
struct ucounts *get_ucounts(struct ucounts *ucounts)
{
unsigned long flags;
if (!ucounts)
return NULL;
spin_lock_irqsave(&ucounts_lock, flags);
if (ucounts->count == INT_MAX) {
WARN_ONCE(1, "ucounts: counter has reached its maximum value");
ucounts = NULL;
} else {
ucounts->count += 1;
}
spin_unlock_irqrestore(&ucounts_lock, flags);
return ucounts;
}
void put_ucounts(struct ucounts *ucounts)
{
unsigned long flags;
@ -194,7 +227,7 @@ struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid,
{
struct ucounts *ucounts, *iter, *bad;
struct user_namespace *tns;
ucounts = get_ucounts(ns, uid);
ucounts = alloc_ucounts(ns, uid);
for (iter = ucounts; iter; iter = tns->ucounts) {
int max;
tns = iter->ns;
@ -237,6 +270,7 @@ static __init int user_namespace_sysctl_init(void)
BUG_ON(!user_header);
BUG_ON(!setup_userns_sysctls(&init_user_ns));
#endif
hlist_add_ucounts(&init_ucounts);
return 0;
}
subsys_initcall(user_namespace_sysctl_init);

3
kernel/user_namespace.c
View File

@ -1340,6 +1340,9 @@ static int userns_install(struct nsset *nsset, struct ns_common *ns)
put_user_ns(cred->user_ns);
set_cred_user_ns(cred, get_user_ns(user_ns));
if (set_cred_ucounts(cred) < 0)
return -EINVAL;
return 0;
}