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perf/core: Fix perf_event_open() vs. execve() race

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Jann reported that the ptrace_may_access() check in
find_lively_task_by_vpid() is racy against exec().

Specifically:

  perf_event_open()		execve()

  ptrace_may_access()
				commit_creds()
  ...				if (get_dumpable() != SUID_DUMP_USER)
				  perf_event_exit_task();
  perf_install_in_context()

would result in installing a counter across the creds boundary.

Fix this by wrapping lots of perf_event_open() in cred_guard_mutex.
This should be fine as perf_event_exit_task() is already called with
cred_guard_mutex held, so all perf locks already nest inside it.

Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2016-04-26 11:36:53 +02:00 committed by Ingo Molnar
parent 0a25556f84
commit 79c9ce57eb
1 changed files with 36 additions and 16 deletions
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52
kernel/events/core.c
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@ -1106,6 +1106,7 @@ static void put_ctx(struct perf_event_context *ctx)
* function.
*
* Lock order:
* cred_guard_mutex
* task_struct::perf_event_mutex
* perf_event_context::mutex
* perf_event::child_mutex;
@ -3421,7 +3422,6 @@ static struct task_struct *
find_lively_task_by_vpid(pid_t vpid)
{
struct task_struct *task;
int err;
rcu_read_lock();
if (!vpid)
@ -3435,16 +3435,7 @@ find_lively_task_by_vpid(pid_t vpid)
if (!task)
return ERR_PTR(-ESRCH);
/* Reuse ptrace permission checks for now. */
err = -EACCES;
if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS))
goto errout;
return task;
errout:
put_task_struct(task);
return ERR_PTR(err);
}
/*
@ -8414,6 +8405,24 @@ SYSCALL_DEFINE5(perf_event_open,
get_online_cpus();
if (task) {
err = mutex_lock_interruptible(&task->signal->cred_guard_mutex);
if (err)
goto err_cpus;
/*
* Reuse ptrace permission checks for now.
*
* We must hold cred_guard_mutex across this and any potential
* perf_install_in_context() call for this new event to
* serialize against exec() altering our credentials (and the
* perf_event_exit_task() that could imply).
*/
err = -EACCES;
if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS))
goto err_cred;
}
if (flags & PERF_FLAG_PID_CGROUP)
cgroup_fd = pid;
@ -8421,7 +8430,7 @@ SYSCALL_DEFINE5(perf_event_open,
NULL, NULL, cgroup_fd);
if (IS_ERR(event)) {
err = PTR_ERR(event);
goto err_cpus;
goto err_cred;
}
if (is_sampling_event(event)) {
@ -8480,11 +8489,6 @@ SYSCALL_DEFINE5(perf_event_open,
goto err_context;
}
if (task) {
put_task_struct(task);
task = NULL;
}
/*
* Look up the group leader (we will attach this event to it):
*/
@ -8582,6 +8586,11 @@ SYSCALL_DEFINE5(perf_event_open,
WARN_ON_ONCE(ctx->parent_ctx);
/*
* This is the point on no return; we cannot fail hereafter. This is
* where we start modifying current state.
*/
if (move_group) {
/*
* See perf_event_ctx_lock() for comments on the details
@ -8653,6 +8662,11 @@ SYSCALL_DEFINE5(perf_event_open,
mutex_unlock(&gctx->mutex);
mutex_unlock(&ctx->mutex);
if (task) {
mutex_unlock(&task->signal->cred_guard_mutex);
put_task_struct(task);
}
put_online_cpus();
mutex_lock(&current->perf_event_mutex);
@ -8685,6 +8699,9 @@ SYSCALL_DEFINE5(perf_event_open,
*/
if (!event_file)
free_event(event);
err_cred:
if (task)
mutex_unlock(&task->signal->cred_guard_mutex);
err_cpus:
put_online_cpus();
err_task:
@ -8969,6 +8986,9 @@ static void perf_event_exit_task_context(struct task_struct *child, int ctxn)
/*
* When a child task exits, feed back event values to parent events.
*
* Can be called with cred_guard_mutex held when called from
* install_exec_creds().
*/
void perf_event_exit_task(struct task_struct *child)
{