tree 3f5eb4b4390ea71031eb2c93261052e6698cbdc1 parent 3f024c1a4bc8ef9a149879351ce8b3aa749e0c2f author David Meybohm <[EMAIL PROTECTED]> Tue, 23 Aug 2005 03:11:08 -0700 committer Linus Torvalds <[EMAIL PROTECTED]> Wed, 24 Aug 2005 01:44:29 -0700
[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 <[EMAIL PROTECTED]> Signed-off-by: Andrew Morton <[EMAIL PROTECTED]> Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]> kernel/timer.c | 2 +- 1 files changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/timer.c b/kernel/timer.c --- 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; - To unsubscribe from this list: send the line "unsubscribe git-commits-head" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html