From eac15e252010c1189a5c0f461364dbe2cd2a68b1 Mon Sep 17 00:00:00 2001
From: "Dustin L. Howett" <dustin@howett.net>
Date: Thu, 9 May 2024 18:59:17 -0500
Subject: [PATCH] rar4 reader: protect copy_from_lzss_window_to_unp() (#2172)

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 constructed 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.

CVE: CVE-2024-20696
Upstream-Status: Backport [https://github.com/libarchive/libarchive/commit/eac15e252010c1189a5c0f461364dbe2cd2a68b1]

Signed-off-by: Nitin Wankhade <nitin.wankhade@kpit.com>
---

--- a/libarchive/archive_read_support_format_rar.c	2024-04-26 14:52:59.000000000 +0530
+++ b/libarchive/archive_read_support_format_rar.c	2024-12-12 07:35:33.287412704 +0530
@@ -432,7 +432,7 @@ static int make_table_recurse(struct arc
                               struct huffman_table_entry *, int, int);
 static int expand(struct archive_read *, int64_t *);
 static int copy_from_lzss_window_to_unp(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 *);
 static int parse_filter(struct archive_read *, const uint8_t *, uint16_t,
                         uint8_t);
@@ -2060,7 +2060,7 @@ 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_to_unp(a, buff, rar->offset, (int)bs);
+      ret = copy_from_lzss_window_to_unp(a, buff, rar->offset, bs);
       if (ret != ARCHIVE_OK)
         return (ret);
       rar->offset += bs;
@@ -2213,7 +2213,7 @@ 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_to_unp(a, buff, rar->offset, (int)bs);
+    ret = copy_from_lzss_window_to_unp(a, buff, rar->offset, bs);
     if (ret != ARCHIVE_OK)
       return (ret);
     rar->offset += bs;
@@ -3094,11 +3094,16 @@ copy_from_lzss_window(struct archive_rea
 
 static int
 copy_from_lzss_window_to_unp(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)
@@ -3110,17 +3115,17 @@ copy_from_lzss_window_to_unp(struct arch
   }
 
   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],
@@ -3130,9 +3135,7 @@ copy_from_lzss_window_to_unp(struct arch
              &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)
@@ -3140,6 +3143,11 @@ copy_from_lzss_window_to_unp(struct arch
   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 *