perf: fix perf bug in fork()

Oleg noticed that a cleanup by Sylvain actually uncovered a bug; by
calling perf_event_free_task() when failing sched_fork() we will not yet
have done the memset() on ->perf_event_ctxp[] and will therefore try and
'free' the inherited contexts, which are still in use by the parent
process.  This is bad..

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Sylvain 'ythier' Hitier <sylvain.hitier@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 6 insertions, 3 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index d640a8b4dcbc..963bf139e2b2 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7948,8 +7948,10 @@ int perf_event_init_task(struct task_struct *child)
 
         for_each_task_context_nr(ctxn) {
                 ret = perf_event_init_context(child, ctxn);
-                if (ret)
+                if (ret) {
+                        perf_event_free_task(child);
                         return ret;
+                }
         }
 
         return 0;
diff --git a/kernel/fork.c b/kernel/fork.c
index 0cf9cdb6e491..a91e47d86de2 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1360,7 +1360,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
                 goto bad_fork_cleanup_policy;
         retval = audit_alloc(p);
         if (retval)
-                goto bad_fork_cleanup_policy;
+                goto bad_fork_cleanup_perf;
         /* copy all the process information */
         shm_init_task(p);
         retval = copy_semundo(clone_flags, p);
@@ -1566,8 +1566,9 @@ bad_fork_cleanup_semundo:
         exit_sem(p);
 bad_fork_cleanup_audit:
         audit_free(p);
-bad_fork_cleanup_policy:
+bad_fork_cleanup_perf:
         perf_event_free_task(p);
+bad_fork_cleanup_policy:
 #ifdef CONFIG_NUMA
         mpol_put(p->mempolicy);
 bad_fork_cleanup_threadgroup_lock: