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authorMarco Elver <elver@google.com>2021-07-05 10:44:53 +0200
committerPeter Zijlstra <peterz@infradead.org>2021-07-16 18:46:38 +0200
commitb068fc04de10fff8974f6ef32b861ad134d94ba4 (patch)
treecb1131829c9f6e3a06c46d98570abae7102ce528
parentperf: Fix required permissions if sigtrap is requested (diff)
downloadlinux-b068fc04de10fff8974f6ef32b861ad134d94ba4.tar.xz
linux-b068fc04de10fff8974f6ef32b861ad134d94ba4.zip
perf: Refactor permissions check into perf_check_permission()
Refactor the permission check in perf_event_open() into a helper perf_check_permission(). This makes the permission check logic more readable (because we no longer have a negated disjunction). Add a comment mentioning the ptrace check also checks the uid. No functional change intended. Signed-off-by: Marco Elver <elver@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Dmitry Vyukov <dvyukov@google.com> Link: https://lore.kernel.org/r/20210705084453.2151729-2-elver@google.com
-rw-r--r--kernel/events/core.c58
1 files changed, 32 insertions, 26 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c
index c13730b7ac01..1cb1f9b8392e 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -11917,6 +11917,37 @@ again:
return gctx;
}
+static bool
+perf_check_permission(struct perf_event_attr *attr, struct task_struct *task)
+{
+ unsigned int ptrace_mode = PTRACE_MODE_READ_REALCREDS;
+ bool is_capable = perfmon_capable();
+
+ if (attr->sigtrap) {
+ /*
+ * perf_event_attr::sigtrap sends signals to the other task.
+ * Require the current task to also have CAP_KILL.
+ */
+ rcu_read_lock();
+ is_capable &= ns_capable(__task_cred(task)->user_ns, CAP_KILL);
+ rcu_read_unlock();
+
+ /*
+ * If the required capabilities aren't available, checks for
+ * ptrace permissions: upgrade to ATTACH, since sending signals
+ * can effectively change the target task.
+ */
+ ptrace_mode = PTRACE_MODE_ATTACH_REALCREDS;
+ }
+
+ /*
+ * Preserve ptrace permission check for backwards compatibility. The
+ * ptrace check also includes checks that the current task and other
+ * task have matching uids, and is therefore not done here explicitly.
+ */
+ return is_capable || ptrace_may_access(task, ptrace_mode);
+}
+
/**
* sys_perf_event_open - open a performance event, associate it to a task/cpu
*
@@ -12158,43 +12189,18 @@ SYSCALL_DEFINE5(perf_event_open,
}
if (task) {
- unsigned int ptrace_mode = PTRACE_MODE_READ_REALCREDS;
- bool is_capable;
-
err = down_read_interruptible(&task->signal->exec_update_lock);
if (err)
goto err_file;
- is_capable = perfmon_capable();
- if (attr.sigtrap) {
- /*
- * perf_event_attr::sigtrap sends signals to the other
- * task. Require the current task to also have
- * CAP_KILL.
- */
- rcu_read_lock();
- is_capable &= ns_capable(__task_cred(task)->user_ns, CAP_KILL);
- rcu_read_unlock();
-
- /*
- * If the required capabilities aren't available, checks
- * for ptrace permissions: upgrade to ATTACH, since
- * sending signals can effectively change the target
- * task.
- */
- ptrace_mode = PTRACE_MODE_ATTACH_REALCREDS;
- }
-
/*
- * Preserve ptrace permission check for backwards compatibility.
- *
* We must hold exec_update_lock 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 (!is_capable && !ptrace_may_access(task, ptrace_mode))
+ if (!perf_check_permission(&attr, task))
goto err_cred;
}