File CVE-2024-20696.patch of Package libarchive.34318

From 020c40df9e31ec727201a8e3ddf1f94093f8fc02 Mon Sep 17 00:00:00 2001
From: "Dustin L. Howett" <dustin@howett.net>
Date: Mon, 15 Jan 2024 22:16:27 -0600
Subject: [PATCH] rar4 reader: protect copy_..._to_unp from too-big or
 too-small length

copy_from_lzss_window_to_unp unnecessarily took an `int` parameter where
both of its callers were holding a `size_t`.

A lzss opcode chain could be cosntructed that resulted in a negative
copy length, which when passed into memcpy would result in a very, very
large positive number.

Switching copy_from_lzss_window_to_unp to take a `size_t` allows it to
properly bounds-check length.

In addition, this patch also ensures that `length` is not itself larger
than the destination buffer.
---
 libarchive/archive_read_support_format_rar.c | 28 +++++++++++++-------
 1 file changed, 18 insertions(+), 10 deletions(-)

Index: b/libarchive/archive_read_support_format_rar.c
===================================================================
--- a/libarchive/archive_read_support_format_rar.c
+++ b/libarchive/archive_read_support_format_rar.c
@@ -358,7 +358,7 @@ static int make_table_recurse(struct arc
                               struct huffman_table_entry *, int, int);
 static int64_t expand(struct archive_read *, int64_t);
 static int copy_from_lzss_window(struct archive_read *, const void **,
-                                   int64_t, int);
+                                   int64_t, size_t);
 static const void *rar_read_ahead(struct archive_read *, size_t, ssize_t *);
 
 /*
@@ -1936,7 +1936,7 @@ read_data_compressed(struct archive_read
         bs = rar->unp_buffer_size - rar->unp_offset;
       else
         bs = (size_t)rar->bytes_uncopied;
-      ret = copy_from_lzss_window(a, buff, rar->offset, (int)bs);
+      ret = copy_from_lzss_window(a, buff, rar->offset, bs);
       if (ret != ARCHIVE_OK)
         return (ret);
       rar->offset += bs;
@@ -2065,7 +2065,7 @@ read_data_compressed(struct archive_read
       bs = rar->unp_buffer_size - rar->unp_offset;
     else
       bs = (size_t)rar->bytes_uncopied;
-    ret = copy_from_lzss_window(a, buff, rar->offset, (int)bs);
+    ret = copy_from_lzss_window(a, buff, rar->offset, bs);
     if (ret != ARCHIVE_OK)
       return (ret);
     rar->offset += bs;
@@ -2923,11 +2923,16 @@ bad_data:
 
 static int
 copy_from_lzss_window(struct archive_read *a, const void **buffer,
-                        int64_t startpos, int length)
+                        int64_t startpos, size_t length)
 {
   int windowoffs, firstpart;
   struct rar *rar = (struct rar *)(a->format->data);
 
+  if (length > rar->unp_buffer_size)
+  {
+    goto fatal;
+  }
+
   if (!rar->unp_buffer)
   {
     if ((rar->unp_buffer = malloc(rar->unp_buffer_size)) == NULL)
@@ -2939,17 +2944,17 @@ copy_from_lzss_window(struct archive_rea
   }
 
   windowoffs = lzss_offset_for_position(&rar->lzss, startpos);
-  if(windowoffs + length <= lzss_size(&rar->lzss)) {
+  if(windowoffs + length <= (size_t)lzss_size(&rar->lzss)) {
     memcpy(&rar->unp_buffer[rar->unp_offset], &rar->lzss.window[windowoffs],
            length);
-  } else if (length <= lzss_size(&rar->lzss)) {
+  } else if (length <= (size_t)lzss_size(&rar->lzss)) {
     firstpart = lzss_size(&rar->lzss) - windowoffs;
     if (firstpart < 0) {
       archive_set_error(&a->archive, ARCHIVE_ERRNO_FILE_FORMAT,
                         "Bad RAR file data");
       return (ARCHIVE_FATAL);
     }
-    if (firstpart < length) {
+    if ((size_t)firstpart < length) {
       memcpy(&rar->unp_buffer[rar->unp_offset],
              &rar->lzss.window[windowoffs], firstpart);
       memcpy(&rar->unp_buffer[rar->unp_offset + firstpart],
@@ -2959,9 +2964,7 @@ copy_from_lzss_window(struct archive_rea
              &rar->lzss.window[windowoffs], length);
     }
   } else {
-      archive_set_error(&a->archive, ARCHIVE_ERRNO_FILE_FORMAT,
-                        "Bad RAR file data");
-      return (ARCHIVE_FATAL);
+      goto fatal;
   }
   rar->unp_offset += length;
   if (rar->unp_offset >= rar->unp_buffer_size)
@@ -2969,6 +2972,11 @@ copy_from_lzss_window(struct archive_rea
   else
     *buffer = NULL;
   return (ARCHIVE_OK);
+
+fatal:
+  archive_set_error(&a->archive, ARCHIVE_ERRNO_FILE_FORMAT,
+                    "Bad RAR file data");
+  return (ARCHIVE_FATAL);
 }
 
 static const void *