Commit 9c2b9d30 authored Sep 29, 2014 by Peter Zijlstra Committed by Ingo Molnar Oct 03, 2014

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 and might explain some outstanding fuzzer failures ...

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: Aaron Tomlin <atomlin@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Daeseok Youn <daeseok.youn@gmail.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20140929101201.GE5430@worktop


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 211de6eb

kernel/events/core.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -7956,9 +7956,11 @@ 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;
		}

kernel/fork.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -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:

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