From b4b2641843db124637fa3d2cb2101982035dcc82 Mon Sep 17 00:00:00 2001 From: Paul Jackson Date: Sun, 8 Jan 2006 01:01:53 -0800 Subject: [PATCH] [PATCH] cpuset: fork hook fix Fix obscure, never seen in real life, cpuset fork race. The cpuset_fork() call in fork.c was setting up the correct task->cpuset pointer after the tasklist_lock was dropped, which briefly exposed the newly forked process with an unsafe (copied from parent without locks or usage counter increment) cpuset pointer. In theory, that exposed cpuset pointer could have been pointing at a cpuset that was already freed and removed, and in theory another task that had been sitting on the tasklist_lock waiting to scan the task list could have raced down the entire tasklist, found our new child at the far end, and dereferenced that bogus cpuset pointer. To fix, setup up the correct cpuset pointer in the new child by calling cpuset_fork() before the new task is linked into the tasklist, and with that, add a fork failure case, to dereference that cpuset, if the fork fails along the way, after cpuset_fork() was called. Had to remove a BUG_ON() from cpuset_exit(), because it was no longer valid - the call to cpuset_exit() from a failed fork would not have PF_EXITING set. Signed-off-by: Paul Jackson Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/cpuset.c | 4 +--- kernel/fork.c | 6 ++++-- 2 files changed, 5 insertions(+), 5 deletions(-) diff --git a/kernel/cpuset.c b/kernel/cpuset.c index 3ea63da11d7..d9349cc48b9 100644 --- a/kernel/cpuset.c +++ b/kernel/cpuset.c @@ -1821,15 +1821,13 @@ void cpuset_fork(struct task_struct *child) * * We don't need to task_lock() this reference to tsk->cpuset, * because tsk is already marked PF_EXITING, so attach_task() won't - * mess with it. + * mess with it, or task is a failed fork, never visible to attach_task. **/ void cpuset_exit(struct task_struct *tsk) { struct cpuset *cs; - BUG_ON(!(tsk->flags & PF_EXITING)); - cs = tsk->cpuset; tsk->cpuset = NULL; diff --git a/kernel/fork.c b/kernel/fork.c index 7fe3adfa65c..7992ee759d8 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -972,12 +972,13 @@ static task_t *copy_process(unsigned long clone_flags, p->io_context = NULL; p->io_wait = NULL; p->audit_context = NULL; + cpuset_fork(p); #ifdef CONFIG_NUMA p->mempolicy = mpol_copy(p->mempolicy); if (IS_ERR(p->mempolicy)) { retval = PTR_ERR(p->mempolicy); p->mempolicy = NULL; - goto bad_fork_cleanup; + goto bad_fork_cleanup_cpuset; } #endif @@ -1148,7 +1149,6 @@ static task_t *copy_process(unsigned long clone_flags, total_forks++; write_unlock_irq(&tasklist_lock); proc_fork_connector(p); - cpuset_fork(p); retval = 0; fork_out: @@ -1180,7 +1180,9 @@ bad_fork_cleanup_security: bad_fork_cleanup_policy: #ifdef CONFIG_NUMA mpol_free(p->mempolicy); +bad_fork_cleanup_cpuset: #endif + cpuset_exit(p); bad_fork_cleanup: if (p->binfmt) module_put(p->binfmt->module);