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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
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22
kernel/futex.c
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@@ -439,15 +439,20 @@ static void free_pi_state(struct futex_pi_state *pi_state)
static struct task_struct * futex_find_get_task(pid_t pid)
{
struct task_struct *p;
uid_t euid = current_euid();
const struct cred *cred = current_cred(), *pcred;
rcu_read_lock();
p = find_task_by_vpid(pid);
if (!p || (euid != p->cred->euid &&
euid != p->cred->uid))
if (!p) {
p = ERR_PTR(-ESRCH);
else
get_task_struct(p);
} else {
pcred = __task_cred(p);
if (cred->euid != pcred->euid &&
cred->euid != pcred->uid)
p = ERR_PTR(-ESRCH);
else
get_task_struct(p);
}
rcu_read_unlock();
@@ -1831,7 +1836,7 @@ sys_get_robust_list(int pid, struct robust_list_head __user * __user *head_ptr,
{
struct robust_list_head __user *head;
unsigned long ret;
uid_t euid = current_euid();
const struct cred *cred = current_cred(), *pcred;
if (!futex_cmpxchg_enabled)
return -ENOSYS;
@@ -1847,8 +1852,9 @@ sys_get_robust_list(int pid, struct robust_list_head __user * __user *head_ptr,
if (!p)
goto err_unlock;
ret = -EPERM;
if (euid != p->cred->euid &&
euid != p->cred->uid &&
pcred = __task_cred(p);
if (cred->euid != pcred->euid &&
cred->euid != pcred->uid &&
!capable(CAP_SYS_PTRACE))
goto err_unlock;
head = p->robust_list;