Messages in this thread Patch in this message | | | Date | Thu, 16 Mar 2017 13:47:48 +0100 | From | Peter Zijlstra <> | Subject | [PATCH 1/4] perf: Fix use-after-free in perf_release() |
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Dmitry reported syzcaller tripped a use-after-free in perf_release().
After much puzzlement Oleg spotted the below scenario:
Task1 Task2
fork() perf_event_init_task() /* ... */ goto bad_fork_$foo; /* ... */ perf_event_free_task() mutex_lock(ctx->lock) perf_free_event(B)
perf_event_release_kernel(A) mutex_lock(A->child_mutex) list_for_each_entry(child, ...) { /* child == B */ ctx = B->ctx; get_ctx(ctx); mutex_unlock(A->child_mutex);
mutex_lock(A->child_mutex) list_del_init(B->child_list) mutex_unlock(A->child_mutex)
/* ... */
mutex_unlock(ctx->lock); put_ctx() /* >0 */ free_task(); mutex_lock(ctx->lock); mutex_lock(A->child_mutex); /* ... */ mutex_unlock(A->child_mutex); mutex_unlock(ctx->lock) put_ctx() /* 0 */ ctx->task && !TOMBSTONE put_task_struct() /* UAF */
This patch closes the hole by making perf_event_free_task() destroy the task <-> ctx relation such that perf_event_release_kernel() will no longer observe the now dead task.
Cc: Arnaldo Carvalho de Melo <acme@kernel.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: stable@vger.kernel.org Fixes: c6e5b73242d2 ("perf: Synchronously clean up child events") Reported-by: Dmitry Vyukov <dvyukov@google.com> Spotted-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: http://lkml.kernel.org/r/20170314155949.GE32474@worktop --- kernel/events/core.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
--- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -10556,6 +10556,17 @@ void perf_event_free_task(struct task_st continue; mutex_lock(&ctx->mutex); + raw_spin_lock_irq(&ctx->lock); + /* + * Destroy the task <-> ctx relation and mark the context dead. + * + * This is important because even though the task hasn't been + * exposed yet the context has been (through child_list). + */ + RCU_INIT_POINTER(task->perf_event_ctxp[ctxn], NULL); + WRITE_ONCE(ctx->task, TASK_TOMBSTONE); + put_task_struct(task); /* cannot be last */ + raw_spin_unlock_irq(&ctx->lock); again: list_for_each_entry_safe(event, tmp, &ctx->pinned_groups, group_entry)
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