From 5e4aabfcaae66b6a169dfe4fb623c2f4d9da5b89 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maciej=20=C5=BBenczykowski?= <maze@google.com>
Date: Mon, 27 Jun 2022 01:15:53 -0700
Subject: [PATCH] Perform map chmod *before* chown
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

After we chown, we potentially are no longer the owner (if we chown'ed
to a different uid then AID_ROOT) and thus can no longer chmod.

If we chmod before we chown, this problem is eliminated.

This fixes uid != AID_ROOT for maps.

Bug: 218408035
Bug: 237716689
Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: Ifbbe37d8dceff245d4def950712f1847615d5856
---
 libbpf_android/Loader.cpp | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/libbpf_android/Loader.cpp b/libbpf_android/Loader.cpp
index 2983c76..2c0db08 100644
--- a/libbpf_android/Loader.cpp
+++ b/libbpf_android/Loader.cpp
@@ -30,9 +30,9 @@
 #include <sys/wait.h>
 #include <unistd.h>
 
-// This is BpfLoader v0.20
+// This is BpfLoader v0.21
 #define BPFLOADER_VERSION_MAJOR 0u
-#define BPFLOADER_VERSION_MINOR 20u
+#define BPFLOADER_VERSION_MINOR 21u
 #define BPFLOADER_VERSION ((BPFLOADER_VERSION_MAJOR << 16) | BPFLOADER_VERSION_MINOR)
 
 #include "bpf/BpfUtils.h"
@@ -873,13 +873,6 @@ static int createMaps(const char* elfPath, ifstream& elfFile, vector<unique_fd>&
                 ret = bpf_obj_pin(fd, mapPinLoc.c_str());
                 if (ret) return -errno;
             }
-            ret = chown(mapPinLoc.c_str(), (uid_t)md[i].uid, (gid_t)md[i].gid);
-            if (ret) {
-                int err = errno;
-                ALOGE("chown(%s, %u, %u) = %d [%d:%s]", mapPinLoc.c_str(), md[i].uid, md[i].gid,
-                      ret, err, strerror(err));
-                return -err;
-            }
             ret = chmod(mapPinLoc.c_str(), md[i].mode);
             if (ret) {
                 int err = errno;
@@ -887,6 +880,13 @@ static int createMaps(const char* elfPath, ifstream& elfFile, vector<unique_fd>&
                       strerror(err));
                 return -err;
             }
+            ret = chown(mapPinLoc.c_str(), (uid_t)md[i].uid, (gid_t)md[i].gid);
+            if (ret) {
+                int err = errno;
+                ALOGE("chown(%s, %u, %u) = %d [%d:%s]", mapPinLoc.c_str(), md[i].uid, md[i].gid,
+                      ret, err, strerror(err));
+                return -err;
+            }
         }
 
         struct bpf_map_info map_info = {};