pids: sys_getpgid: fix unsafe *pid usage, s/tasklist/rcu/
1. sys_getpgid() needs rcu_read_lock() to derive the pgrp _nr, even if
the task is current, otherwise we can race with another thread which
does sys_setpgid().
2. Use rcu_read_lock() instead of tasklist_lock when pid != 0, make sure
that we don't use the NULL pid if the task exits right after successful
find_task_by_vpid().
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/sys.c b/kernel/sys.c
index ddd28e2..895d2d4 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -991,31 +991,37 @@
asmlinkage long sys_getpgid(pid_t pid)
{
- if (!pid)
- return task_pgrp_vnr(current);
- else {
- int retval;
- struct task_struct *p;
+ struct task_struct *p;
+ struct pid *grp;
+ int retval;
- read_lock(&tasklist_lock);
- p = find_task_by_vpid(pid);
+ rcu_read_lock();
+ if (!pid)
+ grp = task_pgrp(current);
+ else {
retval = -ESRCH;
- if (p) {
- retval = security_task_getpgid(p);
- if (!retval)
- retval = task_pgrp_vnr(p);
- }
- read_unlock(&tasklist_lock);
- return retval;
+ p = find_task_by_vpid(pid);
+ if (!p)
+ goto out;
+ grp = task_pgrp(p);
+ if (!grp)
+ goto out;
+
+ retval = security_task_getpgid(p);
+ if (retval)
+ goto out;
}
+ retval = pid_vnr(grp);
+out:
+ rcu_read_unlock();
+ return retval;
}
#ifdef __ARCH_WANT_SYS_GETPGRP
asmlinkage long sys_getpgrp(void)
{
- /* SMP - assuming writes are word atomic this is fine */
- return task_pgrp_vnr(current);
+ return sys_getpgid(0);
}
#endif