Fix Perfetto.cpp to silence SELinux warnings

Turns out that statsd leaves some file descriptors opened
without the O_CLOEXEC flag. This CL mass-closes file descriptors
up to a realistic number of FDs. This is to avoid SELinux complaining
about perfetto accessing these files from the statsd domain.

With this change perfetto works with statsd without disabling SELinux.
Relevant SELinux CL:
https://android-review.googlesource.com/c/platform/system/sepolicy/+/598774

Change-Id: I745d621937fbc9b20a4c733948cd0dd24dd6e8b2

1 files changed, 20 insertions, 4 deletions

diff --git a/cmds/statsd/src/external/Perfetto.cpp b/cmds/statsd/src/external/Perfetto.cpp
index f7b33e77c557..1d8a96850c4b 100644
--- a/cmds/statsd/src/external/Perfetto.cpp
+++ b/cmds/statsd/src/external/Perfetto.cpp
@@ -20,6 +20,7 @@
 
 #include <android-base/unique_fd.h>
 #include <errno.h>
+#include <fcntl.h>
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <unistd.h>
@@ -65,11 +66,26 @@ bool CollectPerfettoTraceAndUploadToDropbox(const PerfettoDetails& config) {
 
         // Replace stdin with |readPipe| so the main process can write into it.
         if (dup2(readPipe.get(), STDIN_FILENO) < 0) _exit(1);
+        readPipe.reset();
+
+        // Replace stdout/stderr with /dev/null and close any other file
+        // descriptor. This is to avoid SELinux complaining about perfetto
+        // trying to access files accidentally left open by statsd (i.e. files
+        // that have been opened without the O_CLOEXEC flag).
+        int devNullFd = open("/dev/null", O_RDWR | O_CLOEXEC);
+        if (dup2(devNullFd, STDOUT_FILENO) < 0) _exit(2);
+        if (dup2(devNullFd, STDERR_FILENO) < 0) _exit(3);
+        close(devNullFd);
+        for (int i = 0; i < 1024; i++) {
+            if (i != STDIN_FILENO && i != STDOUT_FILENO && i != STDERR_FILENO) close(i);
+        }
+
         execl("/system/bin/perfetto", "perfetto", "--background", "--config", "-", "--dropbox",
               kDropboxTag, nullptr);
 
-        // execl() doesn't return in case of success, if we get here something failed.
-        _exit(1);
+        // execl() doesn't return in case of success, if we get here something
+        // failed.
+        _exit(4);
     }
 
     // Main process.
@@ -93,8 +109,8 @@ bool CollectPerfettoTraceAndUploadToDropbox(const PerfettoDetails& config) {
         return false;
     }
 
-    // This does NOT wait for the full duration of the trace. It just waits until the process
-    // has read the config from stdin and detached.
+    // This does NOT wait for the full duration of the trace. It just waits until
+    // the process has read the config from stdin and detached.
     int childStatus = 0;
     waitpid(pid, &childStatus, 0);
     if (!WIFEXITED(childStatus) || WEXITSTATUS(childStatus) != 0) {