fix: potential out-of-range error in io's readOrWritePiece() (#2413)

libtransmission/inout.cc

@@ -50,9 +50,10 @@ static int readOrWriteBytes(
     void* buf,
     size_t buflen)
 {
+    TR_ASSERT(file_index < tor->fileCount());
+
     int err = 0;
     bool const doWrite = ioMode >= TR_IO_WRITE;
-
     auto const file_size = tor->fileSize(file_index);
     TR_ASSERT(file_size == 0 || file_offset < file_size);
     TR_ASSERT(file_offset + buflen <= file_size);
@@ -174,14 +175,15 @@ static int readOrWritePiece(
         err = readOrWriteBytes(tor->session, tor, ioMode, file_index, file_offset, buf, bytes_this_pass);
         buf += bytes_this_pass;
         buflen -= bytes_this_pass;
-        ++file_index;
-        file_offset = 0;
 
         if (err != 0 && ioMode == TR_IO_WRITE && tor->error != TR_STAT_LOCAL_ERROR)
         {
             auto const path = tr_strvPath(tor->downloadDir().sv(), tor->fileSubpath(file_index));
             tor->setLocalError(tr_strvJoin(tr_strerror(err), " ("sv, path, ")"sv));
         }
+
+        ++file_index;
+        file_offset = 0;
     }
 
     return err;

libtransmission/torrent-metainfo.cc

@@ -25,6 +25,7 @@
 #include "log.h"
 #include "quark.h"
 #include "torrent-metainfo.h"
+#include "tr-assert.h"
 #include "utils.h"
 #include "variant.h"
 #include "web-utils.h"
@@ -596,3 +597,24 @@ bool tr_torrent_metainfo::migrateFile(
         new_filename.c_str());
     return true;
 }
+
+std::string const& tr_torrent_metainfo::fileSubpath(tr_file_index_t i) const
+{
+    TR_ASSERT(i < fileCount());
+
+    return files_.at(i).path();
+}
+
+void tr_torrent_metainfo::setFileSubpath(tr_file_index_t i, std::string_view subpath)
+{
+    TR_ASSERT(i < fileCount());
+
+    files_.at(i).setSubpath(subpath);
+}
+
+uint64_t tr_torrent_metainfo::fileSize(tr_file_index_t i) const
+{
+    TR_ASSERT(i < fileCount());
+
+    return files_.at(i).size();
+}

libtransmission/torrent-metainfo.h

@@ -97,11 +97,11 @@ public:
         return blockInfo().totalSize();
     }
 
-    auto const& comment() const
+    [[nodiscard]] auto const& comment() const
     {
         return comment_;
     }
-    auto const& creator() const
+    [[nodiscard]] auto const& creator() const
     {
         return creator_;
     }
@@ -110,22 +110,16 @@ public:
         return source_;
     }
 
-    auto fileCount() const
+    [[nodiscard]] auto fileCount() const
     {
         return std::size(files_);
     }
-    std::string const& fileSubpath(tr_file_index_t i) const
-    {
-        return files_.at(i).path();
-    }
-    void setFileSubpath(tr_file_index_t i, std::string_view subpath)
-    {
-        files_.at(i).setSubpath(subpath);
-    }
-    auto fileSize(tr_file_index_t i) const
-    {
-        return files_.at(i).size();
-    }
+
+    [[nodiscard]] std::string const& fileSubpath(tr_file_index_t i) const;
+
+    void setFileSubpath(tr_file_index_t i, std::string_view subpath);
+
+    [[nodiscard]] uint64_t fileSize(tr_file_index_t i) const;
 
     [[nodiscard]] auto const& isPrivate() const
     {