Put fchmod back to the top in SystemNative_CopyFile and only ignore when it fails on android

src/Native/Unix/System.Native/pal_io.c

@@ -1257,7 +1257,27 @@ int32_t SystemNative_CopyFile(intptr_t sourceFd, intptr_t destinationFd)
     int ret;
     struct stat_ sourceStat;
     bool copied = false;
-
+
+    // First, stat the source file.
+    while ((ret = fstat_(inFd, &sourceStat)) < 0 && errno == EINTR);
+    if (ret != 0)
+    {
+        // If we can't stat() it, then we likely don't have permission to read it.
+        return -1;
+    }
+
+    // Then copy permissions.  This fchmod() needs to happen prior to writing anything into
+    // the file to avoid possiblyleaking any private data.
+    while ((ret = fchmod(outFd, sourceStat.st_mode & (S_IRWXU | S_IRWXG | S_IRWXO))) < 0 && errno == EINTR);
+#if !TARGET_ANDROID
+    // On Android, we are not allowed to modify permissions, but the copy should still succeed;
+    // see https://github.com/mono/mono/issues/17133 for details.
+    if (ret != 0)
+    {
+        return -1;
+    }
+#endif
+
 #if HAVE_SENDFILE_4
     // If sendfile is available (Linux), try to use it, as the whole copy
     // can be performed in the kernel, without lots of unnecessary copying.
@@ -1267,6 +1287,7 @@ int32_t SystemNative_CopyFile(intptr_t sourceFd, intptr_t destinationFd)
         return -1;
     }
 
+
     // On 32-bit, if you use 64-bit offsets, the last argument of `sendfile' will be a
     // `size_t' a 32-bit integer while the `st_size' field of the stat structure will be off64_t.
     // So `size' will have to be `uint64_t'. In all other cases, it will be `size_t'.
@@ -1334,24 +1355,6 @@ int32_t SystemNative_CopyFile(intptr_t sourceFd, intptr_t destinationFd)
 #endif
     }
 
-    if (ret != 0)
-    {
-        return -1;
-    }
-
-    // Then copy permissions.
-    while ((ret = fchmod(outFd, sourceStat.st_mode & (S_IRWXU | S_IRWXG | S_IRWXO))) < 0 && errno == EINTR);
-
-// We are ignoring the error on Android because in the case of external storage we are not allowed
-// to modify permissions, but the copy should still succeed.
-// https://github.com/mono/mono/issues/17133
-#if !TARGET_ANDROID
-    if (ret != 0)
-    {
-        return -1;
-    }
-#endif
-
     return 0;
 #endif // HAVE_FCOPYFILE
 }