diff options
authorDavid Meybohm <dmeybohmlkml@bellsouth.net>2005-08-22 13:11:08 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2005-08-23 11:44:29 -0700
commit4c5640cb5f5a6fd780d99397eca028b575cb1206 (patch)
parent3f024c1a4bc8ef9a149879351ce8b3aa749e0c2f (diff)
[PATCH] preempt race in getppid
With CONFIG_PREEMPT && !CONFIG_SMP, it's possible for sys_getppid to return a bogus value if the parent's task_struct gets reallocated after current->group_leader->real_parent is read: asmlinkage long sys_getppid(void) { int pid; struct task_struct *me = current; struct task_struct *parent; parent = me->group_leader->real_parent; RACE HERE => for (;;) { pid = parent->tgid; #ifdef CONFIG_SMP { struct task_struct *old = parent; /* * Make sure we read the pid before re-reading the * parent pointer: */ smp_rmb(); parent = me->group_leader->real_parent; if (old != parent) continue; } #endif break; } return pid; } If the process gets preempted at the indicated point, the parent process can go ahead and call exit() and then get wait()'d on to reap its task_struct. When the preempted process gets resumed, it will not do any further checks of the parent pointer on !CONFIG_SMP: it will read the bad pid and return. So, the same algorithm used when SMP is enabled should be used when preempt is enabled, which will recheck ->real_parent in this case. Signed-off-by: David Meybohm <dmeybohmlkml@bellsouth.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/timer.c b/kernel/timer.c
index f2a11887a726..5377f40723ff 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1023,7 +1023,7 @@ asmlinkage long sys_getppid(void)
parent = me->group_leader->real_parent;
for (;;) {
pid = parent->tgid;
-#ifdef CONFIG_SMP
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT)
struct task_struct *old = parent;