From 671249a3d22ea36be4f8edba368f2cdf0e22f905 Mon Sep 17 00:00:00 2001
From: Bowgo Tsai <bowgotsai@google.com>
Date: Tue, 10 Aug 2021 16:32:37 +0800
Subject: [PATCH] fastboot: fix --disable-verifiation error message

There is an unclear error message if we run
`fastboot --disable-verification flash boot boot.img` on a
AVB-disabled device without a /vbmeta partition.

Error message:
  terminating with uncaught exception of type std::out_of_range: basic_string
  Aborted

This is because the buf->fd of the loaded boot.img is not reset,
before returning from function copy_boot_avb_footer().

Also reset some changes in copy_boot_avb_footer() from commit
If83f785e235569ee8ef0de2b37f11dbd2a9a71f4, to prevent the
unnecessary read of the boot vbmeta if no need to copy the
boot image avb footer.

Bug: 191903922
Test: `fastboot --disable-verification flash boot boot.img` on a device
      without /vbmeta and without setting BOARD_AVB_ENABLE to true.
Change-Id: If84f08f1b2e12c4c6ded5cafda2bd1d30e75c662
---
 fastboot/fastboot.cpp | 31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

diff --git a/fastboot/fastboot.cpp b/fastboot/fastboot.cpp
index c87ce606f..532b52490 100644
--- a/fastboot/fastboot.cpp
+++ b/fastboot/fastboot.cpp
@@ -941,7 +941,8 @@ static void rewrite_vbmeta_buffer(struct fastboot_buffer* buf, bool vbmeta_in_bo
         // Tries to locate top-level vbmeta from boot.img footer.
         uint64_t footer_offset = buf->sz - AVB_FOOTER_SIZE;
         if (0 != data.compare(footer_offset, AVB_FOOTER_MAGIC_LEN, AVB_FOOTER_MAGIC)) {
-            die("Failed to find AVB_FOOTER at offset: %" PRId64, footer_offset);
+            die("Failed to find AVB_FOOTER at offset: %" PRId64 ", is BOARD_AVB_ENABLE true?",
+                footer_offset);
         }
         const AvbFooter* footer = reinterpret_cast<const AvbFooter*>(data.c_str() + footer_offset);
         vbmeta_offset = be64toh(footer->vbmeta_offset);
@@ -1021,6 +1022,24 @@ static void copy_boot_avb_footer(const std::string& partition, struct fastboot_b
         return;
     }
 
+    // If overflows and negative, it should be < buf->sz.
+    int64_t partition_size = static_cast<int64_t>(get_partition_size(partition));
+
+    if (partition_size == buf->sz) {
+        return;
+    }
+    // Some device bootloaders might not implement `fastboot getvar partition-size:boot[_a|_b]`.
+    // In this case, partition_size will be zero.
+    if (partition_size < buf->sz) {
+        fprintf(stderr,
+                "Warning: skip copying boot image avb footer"
+                " (boot partition size: %" PRId64 ", boot image size: %" PRId64 ").\n",
+                partition_size, buf->sz);
+        return;
+    }
+
+    // IMPORTANT: after the following read, we need to reset buf->fd before return (if not die).
+    // Because buf->fd will still be used afterwards.
     std::string data;
     if (!android::base::ReadFdToString(buf->fd, &data)) {
         die("Failed reading from boot");
@@ -1028,17 +1047,9 @@ static void copy_boot_avb_footer(const std::string& partition, struct fastboot_b
 
     uint64_t footer_offset = buf->sz - AVB_FOOTER_SIZE;
     if (0 != data.compare(footer_offset, AVB_FOOTER_MAGIC_LEN, AVB_FOOTER_MAGIC)) {
+        lseek(buf->fd.get(), 0, SEEK_SET);  // IMPORTANT: resets buf->fd before return.
         return;
     }
-    // If overflows and negative, it should be < buf->sz.
-    int64_t partition_size = static_cast<int64_t>(get_partition_size(partition));
-
-    if (partition_size == buf->sz) {
-        return;
-    }
-    if (partition_size < buf->sz) {
-        die("boot partition is smaller than boot image");
-    }
 
     unique_fd fd(make_temporary_fd("boot rewriting"));
     if (!android::base::WriteStringToFd(data, fd)) {