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Subject[PATCH 12/15] kernel: convert cred.usage from atomic_t to refcount_t
Date
refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
---
include/linux/cred.h | 6 +++---
kernel/cred.c | 44 ++++++++++++++++++++++----------------------
2 files changed, 25 insertions(+), 25 deletions(-)

diff --git a/include/linux/cred.h b/include/linux/cred.h
index 00948dd..a9f217b 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -109,7 +109,7 @@ extern bool may_setgroups(void);
* same context as task->real_cred.
*/
struct cred {
- atomic_t usage;
+ refcount_t usage;
#ifdef CONFIG_DEBUG_CREDENTIALS
atomic_t subscribers; /* number of processes subscribed */
void *put_addr;
@@ -222,7 +222,7 @@ static inline bool cap_ambient_invariant_ok(const struct cred *cred)
*/
static inline struct cred *get_new_cred(struct cred *cred)
{
- atomic_inc(&cred->usage);
+ refcount_inc(&cred->usage);
return cred;
}

@@ -262,7 +262,7 @@ static inline void put_cred(const struct cred *_cred)
struct cred *cred = (struct cred *) _cred;

validate_creds(cred);
- if (atomic_dec_and_test(&(cred)->usage))
+ if (refcount_dec_and_test(&(cred)->usage))
__put_cred(cred);
}

diff --git a/kernel/cred.c b/kernel/cred.c
index 8122d7c..49664e5 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -42,7 +42,7 @@ struct group_info init_groups = { .usage = REFCOUNT_INIT(2) };
* The initial credentials for the initial task
*/
struct cred init_cred = {
- .usage = ATOMIC_INIT(4),
+ .usage = REFCOUNT_INIT(4),
#ifdef CONFIG_DEBUG_CREDENTIALS
.subscribers = ATOMIC_INIT(2),
.magic = CRED_MAGIC,
@@ -101,17 +101,17 @@ static void put_cred_rcu(struct rcu_head *rcu)

#ifdef CONFIG_DEBUG_CREDENTIALS
if (cred->magic != CRED_MAGIC_DEAD ||
- atomic_read(&cred->usage) != 0 ||
+ refcount_read(&cred->usage) != 0 ||
read_cred_subscribers(cred) != 0)
panic("CRED: put_cred_rcu() sees %p with"
" mag %x, put %p, usage %d, subscr %d\n",
cred, cred->magic, cred->put_addr,
- atomic_read(&cred->usage),
+ refcount_read(&cred->usage),
read_cred_subscribers(cred));
#else
- if (atomic_read(&cred->usage) != 0)
+ if (refcount_read(&cred->usage) != 0)
panic("CRED: put_cred_rcu() sees %p with usage %d\n",
- cred, atomic_read(&cred->usage));
+ cred, refcount_read(&cred->usage));
#endif

security_cred_free(cred);
@@ -135,10 +135,10 @@ static void put_cred_rcu(struct rcu_head *rcu)
void __put_cred(struct cred *cred)
{
kdebug("__put_cred(%p{%d,%d})", cred,
- atomic_read(&cred->usage),
+ refcount_read(&cred->usage),
read_cred_subscribers(cred));

- BUG_ON(atomic_read(&cred->usage) != 0);
+ BUG_ON(refcount_read(&cred->usage) != 0);
#ifdef CONFIG_DEBUG_CREDENTIALS
BUG_ON(read_cred_subscribers(cred) != 0);
cred->magic = CRED_MAGIC_DEAD;
@@ -159,7 +159,7 @@ void exit_creds(struct task_struct *tsk)
struct cred *cred;

kdebug("exit_creds(%u,%p,%p,{%d,%d})", tsk->pid, tsk->real_cred, tsk->cred,
- atomic_read(&tsk->cred->usage),
+ refcount_read(&tsk->cred->usage),
read_cred_subscribers(tsk->cred));

cred = (struct cred *) tsk->real_cred;
@@ -194,7 +194,7 @@ const struct cred *get_task_cred(struct task_struct *task)
do {
cred = __task_cred((task));
BUG_ON(!cred);
- } while (!atomic_inc_not_zero(&((struct cred *)cred)->usage));
+ } while (!refcount_inc_not_zero(&((struct cred *)cred)->usage));

rcu_read_unlock();
return cred;
@@ -212,7 +212,7 @@ struct cred *cred_alloc_blank(void)
if (!new)
return NULL;

- atomic_set(&new->usage, 1);
+ refcount_set(&new->usage, 1);
#ifdef CONFIG_DEBUG_CREDENTIALS
new->magic = CRED_MAGIC;
#endif
@@ -258,7 +258,7 @@ struct cred *prepare_creds(void)
old = task->cred;
memcpy(new, old, sizeof(struct cred));

- atomic_set(&new->usage, 1);
+ refcount_set(&new->usage, 1);
set_cred_subscribers(new, 0);
get_group_info(new->group_info);
get_uid(new->user);
@@ -335,7 +335,7 @@ int copy_creds(struct task_struct *p, unsigned long clone_flags)
get_cred(p->cred);
alter_cred_subscribers(p->cred, 2);
kdebug("share_creds(%p{%d,%d})",
- p->cred, atomic_read(&p->cred->usage),
+ p->cred, refcount_read(&p->cred->usage),
read_cred_subscribers(p->cred));
atomic_inc(&p->cred->user->processes);
return 0;
@@ -426,7 +426,7 @@ int commit_creds(struct cred *new)
const struct cred *old = task->real_cred;

kdebug("commit_creds(%p{%d,%d})", new,
- atomic_read(&new->usage),
+ refcount_read(&new->usage),
read_cred_subscribers(new));

BUG_ON(task->cred != old);
@@ -435,7 +435,7 @@ int commit_creds(struct cred *new)
validate_creds(old);
validate_creds(new);
#endif
- BUG_ON(atomic_read(&new->usage) < 1);
+ BUG_ON(refcount_read(&new->usage) < 1);

get_cred(new); /* we will require a ref for the subj creds too */

@@ -500,13 +500,13 @@ EXPORT_SYMBOL(commit_creds);
void abort_creds(struct cred *new)
{
kdebug("abort_creds(%p{%d,%d})", new,
- atomic_read(&new->usage),
+ refcount_read(&new->usage),
read_cred_subscribers(new));

#ifdef CONFIG_DEBUG_CREDENTIALS
BUG_ON(read_cred_subscribers(new) != 0);
#endif
- BUG_ON(atomic_read(&new->usage) < 1);
+ BUG_ON(refcount_read(&new->usage) < 1);
put_cred(new);
}
EXPORT_SYMBOL(abort_creds);
@@ -523,7 +523,7 @@ const struct cred *override_creds(const struct cred *new)
const struct cred *old = current->cred;

kdebug("override_creds(%p{%d,%d})", new,
- atomic_read(&new->usage),
+ refcount_read(&new->usage),
read_cred_subscribers(new));

validate_creds(old);
@@ -534,7 +534,7 @@ const struct cred *override_creds(const struct cred *new)
alter_cred_subscribers(old, -1);

kdebug("override_creds() = %p{%d,%d}", old,
- atomic_read(&old->usage),
+ refcount_read(&old->usage),
read_cred_subscribers(old));
return old;
}
@@ -552,7 +552,7 @@ void revert_creds(const struct cred *old)
const struct cred *override = current->cred;

kdebug("revert_creds(%p{%d,%d})", old,
- atomic_read(&old->usage),
+ refcount_read(&old->usage),
read_cred_subscribers(old));

validate_creds(old);
@@ -611,7 +611,7 @@ struct cred *prepare_kernel_cred(struct task_struct *daemon)
validate_creds(old);

*new = *old;
- atomic_set(&new->usage, 1);
+ refcount_set(&new->usage, 1);
set_cred_subscribers(new, 0);
get_uid(new->user);
get_user_ns(new->user_ns);
@@ -735,7 +735,7 @@ static void dump_invalid_creds(const struct cred *cred, const char *label,
printk(KERN_ERR "CRED: ->magic=%x, put_addr=%p\n",
cred->magic, cred->put_addr);
printk(KERN_ERR "CRED: ->usage=%d, subscr=%d\n",
- atomic_read(&cred->usage),
+ refcount_read(&cred->usage),
read_cred_subscribers(cred));
printk(KERN_ERR "CRED: ->*uid = { %d,%d,%d,%d }\n",
from_kuid_munged(&init_user_ns, cred->uid),
@@ -809,7 +809,7 @@ void validate_creds_for_do_exit(struct task_struct *tsk)
{
kdebug("validate_creds_for_do_exit(%p,%p{%d,%d})",
tsk->real_cred, tsk->cred,
- atomic_read(&tsk->cred->usage),
+ refcount_read(&tsk->cred->usage),
read_cred_subscribers(tsk->cred));

__validate_process_creds(tsk, __FILE__, __LINE__);
--
2.7.4
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