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authorPeter Zijlstra <peterz@infradead.org>2016-04-26 11:36:53 +0200
committerIngo Molnar <mingo@kernel.org>2016-04-28 10:32:41 +0200
commit79c9ce57eb2d5f1497546a3946b4ae21b6fdc438 (patch)
treecdbdbbf5fb4887df3623feeb1b7d4f29e4b49d31 /kernel
parent0a25556f84d5f79e68e9502bb1f32a43377ab2bf (diff)
downloadlinux-79c9ce57eb2d5f1497546a3946b4ae21b6fdc438.tar.bz2
perf/core: Fix perf_event_open() vs. execve() race
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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/events/core.c52
1 files changed, 36 insertions, 16 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 2c78b6f47339..4e2ebf6f2f1f 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -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 @@ err_alloc:
*/
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)
{