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CRED: Use RCU to access another task's creds and to release a task's own creds

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Use RCU to access another task's creds and to release a task's own creds.
This means that it will be possible for the credentials of a task to be
replaced without another task (a) requiring a full lock to read them, and (b)
seeing deallocated memory.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: James Morris <jmorris@namei.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>
This commit is contained in:
David Howells 2008-11-14 10:39:19 +11:00 • committed by James Morris
parent 86a264abe5
commit c69e8d9c01
28 changed files with 353 additions and 202 deletions
Download patch file Download diff file Expand all files Collapse all files

64
security/commoncap.c
View file

@ -51,10 +51,13 @@ EXPORT_SYMBOL(cap_netlink_recv);
*/
int cap_capable(struct task_struct *tsk, int cap, int audit)
{
__u32 cap_raised;
/* Derived from include/linux/sched.h:capable. */
if (cap_raised(tsk->cred->cap_effective, cap))
return 0;
return -EPERM;
rcu_read_lock();
cap_raised = cap_raised(__task_cred(tsk)->cap_effective, cap);
rcu_read_unlock();
return cap_raised ? 0 : -EPERM;
}
int cap_settime(struct timespec *ts, struct timezone *tz)
@ -66,34 +69,42 @@ int cap_settime(struct timespec *ts, struct timezone *tz)
int cap_ptrace_may_access(struct task_struct *child, unsigned int mode)
{
/* Derived from arch/i386/kernel/ptrace.c:sys_ptrace. */
if (cap_issubset(child->cred->cap_permitted,
current->cred->cap_permitted))
return 0;
if (capable(CAP_SYS_PTRACE))
return 0;
return -EPERM;
int ret = 0;
rcu_read_lock();
if (!cap_issubset(child->cred->cap_permitted,
current->cred->cap_permitted) &&
!capable(CAP_SYS_PTRACE))
ret = -EPERM;
rcu_read_unlock();
return ret;
}
int cap_ptrace_traceme(struct task_struct *parent)
{
if (cap_issubset(current->cred->cap_permitted,
parent->cred->cap_permitted))
return 0;
if (has_capability(parent, CAP_SYS_PTRACE))
return 0;
return -EPERM;
int ret = 0;
rcu_read_lock();
if (!cap_issubset(current->cred->cap_permitted,
parent->cred->cap_permitted) &&
!has_capability(parent, CAP_SYS_PTRACE))
ret = -EPERM;
rcu_read_unlock();
return ret;
}
int cap_capget (struct task_struct *target, kernel_cap_t *effective,
kernel_cap_t *inheritable, kernel_cap_t *permitted)
{
struct cred *cred = target->cred;
const struct cred *cred;
/* Derived from kernel/capability.c:sys_capget. */
rcu_read_lock();
cred = __task_cred(target);
*effective = cred->cap_effective;
*inheritable = cred->cap_inheritable;
*permitted = cred->cap_permitted;
rcu_read_unlock();
return 0;
}
@ -433,7 +444,7 @@ void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
int cap_bprm_secureexec (struct linux_binprm *bprm)
{
const struct cred *cred = current->cred;
const struct cred *cred = current_cred();
if (cred->uid != 0) {
if (bprm->cap_effective)
@ -511,11 +522,11 @@ static inline void cap_emulate_setxuid (int old_ruid, int old_euid,
if ((old_ruid == 0 || old_euid == 0 || old_suid == 0) &&
(cred->uid != 0 && cred->euid != 0 && cred->suid != 0) &&
!issecure(SECURE_KEEP_CAPS)) {
cap_clear (cred->cap_permitted);
cap_clear (cred->cap_effective);
cap_clear(cred->cap_permitted);
cap_clear(cred->cap_effective);
}
if (old_euid == 0 && cred->euid != 0) {
cap_clear (cred->cap_effective);
cap_clear(cred->cap_effective);
}
if (old_euid != 0 && cred->euid == 0) {
cred->cap_effective = cred->cap_permitted;
@ -582,9 +593,14 @@ int cap_task_post_setuid (uid_t old_ruid, uid_t old_euid, uid_t old_suid,
*/
static int cap_safe_nice(struct task_struct *p)
{
if (!cap_issubset(p->cred->cap_permitted,
current->cred->cap_permitted) &&
!capable(CAP_SYS_NICE))
int is_subset;
rcu_read_lock();
is_subset = cap_issubset(__task_cred(p)->cap_permitted,
current_cred()->cap_permitted);
rcu_read_unlock();
if (!is_subset && !capable(CAP_SYS_NICE))
return -EPERM;
return 0;
}