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

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>

1 files changed, 21 insertions, 11 deletions

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 62fe9b2009b6..7e4877d9dcb5 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -159,6 +159,7 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
 	struct group_info *group_info;
 	int g;
 	struct fdtable *fdt = NULL;
+	const struct cred *cred;
 	pid_t ppid, tpid;
 
 	rcu_read_lock();
@@ -170,6 +171,7 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
 		if (tracer)
 			tpid = task_pid_nr_ns(tracer, ns);
 	}
+	cred = get_cred((struct cred *) __task_cred(p));
 	seq_printf(m,
 		"State:\t%s\n"
 		"Tgid:\t%d\n"
@@ -182,8 +184,8 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
 		task_tgid_nr_ns(p, ns),
 		pid_nr_ns(pid, ns),
 		ppid, tpid,
-		p->cred->uid, p->cred->euid, p->cred->suid, p->cred->fsuid,
-		p->cred->gid, p->cred->egid, p->cred->sgid, p->cred->fsgid);
+		cred->uid, cred->euid, cred->suid, cred->fsuid,
+		cred->gid, cred->egid, cred->sgid, cred->fsgid);
 
 	task_lock(p);
 	if (p->files)
@@ -194,13 +196,12 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
 		fdt ? fdt->max_fds : 0);
 	rcu_read_unlock();
 
-	group_info = p->cred->group_info;
-	get_group_info(group_info);
+	group_info = cred->group_info;
 	task_unlock(p);
 
 	for (g = 0; g < min(group_info->ngroups, NGROUPS_SMALL); g++)
 		seq_printf(m, "%d ", GROUP_AT(group_info, g));
-	put_group_info(group_info);
+	put_cred(cred);
 
 	seq_printf(m, "\n");
 }
@@ -262,7 +263,7 @@ static inline void task_sig(struct seq_file *m, struct task_struct *p)
 		blocked = p->blocked;
 		collect_sigign_sigcatch(p, &ignored, &caught);
 		num_threads = atomic_read(&p->signal->count);
-		qsize = atomic_read(&p->cred->user->sigpending);
+		qsize = atomic_read(&__task_cred(p)->user->sigpending);
 		qlim = p->signal->rlim[RLIMIT_SIGPENDING].rlim_cur;
 		unlock_task_sighand(p, &flags);
 	}
@@ -293,12 +294,21 @@ static void render_cap_t(struct seq_file *m, const char *header,
 
 static inline void task_cap(struct seq_file *m, struct task_struct *p)
 {
-	struct cred *cred = p->cred;
+	const struct cred *cred;
+	kernel_cap_t cap_inheritable, cap_permitted, cap_effective, cap_bset;
 
-	render_cap_t(m, "CapInh:\t", &cred->cap_inheritable);
-	render_cap_t(m, "CapPrm:\t", &cred->cap_permitted);
-	render_cap_t(m, "CapEff:\t", &cred->cap_effective);
-	render_cap_t(m, "CapBnd:\t", &cred->cap_bset);
+	rcu_read_lock();
+	cred = __task_cred(p);
+	cap_inheritable	= cred->cap_inheritable;
+	cap_permitted	= cred->cap_permitted;
+	cap_effective	= cred->cap_effective;
+	cap_bset	= cred->cap_bset;
+	rcu_read_unlock();
+
+	render_cap_t(m, "CapInh:\t", &cap_inheritable);
+	render_cap_t(m, "CapPrm:\t", &cap_permitted);
+	render_cap_t(m, "CapEff:\t", &cap_effective);
+	render_cap_t(m, "CapBnd:\t", &cap_bset);
 }
 
 static inline void task_context_switch_counts(struct seq_file *m,