From 22700942fec895b2d3e5ed6741756deb8666eaae Mon Sep 17 00:00:00 2001

From: Daniel Axtens <dja@axtens.net>

Date: Tue, 4 Dec 2018 00:55:22 +1100

Subject: [PATCH] rar: file split across multi-part archives must match

Fuzzing uncovered some UAF and memory overrun bugs where a file in a

single file archive reported that it was split across multiple

volumes. This was caused by ppmd7 operations calling

rar_br_fillup. This would invoke rar_read_ahead, which would in some

situations invoke archive_read_format_rar_read_header.  That would

check the new file name against the old file name, and if they didn't

match up it would free the ppmd7 buffer and allocate a new

one. However, because the ppmd7 decoder wasn't actually done with the

buffer, it would continue to used the freed buffer. Both reads and

writes to the freed region can be observed.

This is quite tricky to solve: once the buffer has been freed it is

too late, as the ppmd7 decoder functions almost universally assume

success - there's no way for ppmd_read to signal error, nor are there

good ways for functions like Range_Normalise to propagate them. So we

can't detect after the fact that we're in an invalid state - e.g. by

checking rar->cursor, we have to prevent ourselves from ever ending up

there. So, when we are in the dangerous part or rar_read_ahead that

assumes a valid split, we set a flag force read_header to either go

down the path for split files or bail. This means that the ppmd7

decoder keeps a valid buffer and just runs out of data.

Found with a combination of AFL, afl-rb and qsym.

---

 libarchive/archive_read_support_format_rar.c | 9 +++++++++

 1 file changed, 9 insertions(+)

diff --git a/libarchive/archive_read_support_format_rar.c b/libarchive/archive_read_support_format_rar.c

index 6f419c27..a8cc5c94 100644

--- a/libarchive/archive_read_support_format_rar.c

+++ b/libarchive/archive_read_support_format_rar.c

@@ -258,6 +258,7 @@ struct rar

   struct data_block_offsets *dbo;

   unsigned int cursor;

   unsigned int nodes;

+  char filename_must_match;

   /* LZSS members */

   struct huffman_code maincode;

@@ -1560,6 +1561,12 @@ read_header(struct archive_read *a, struct archive_entry *entry,

     }

     return ret;

   }

+  else if (rar->filename_must_match)

+  {

+    archive_set_error(&a->archive, ARCHIVE_ERRNO_FILE_FORMAT,

+      "Mismatch of file parts split across multi-volume archive");

+    return (ARCHIVE_FATAL);

+  }

   rar->filename_save = (char*)realloc(rar->filename_save,

                                       filename_size + 1);

@@ -2933,12 +2940,14 @@ rar_read_ahead(struct archive_read *a, size_t min, ssize_t *avail)

     else if (*avail == 0 && rar->main_flags & MHD_VOLUME &&

       rar->file_flags & FHD_SPLIT_AFTER)

     {

+      rar->filename_must_match = 1;

       ret = archive_read_format_rar_read_header(a, a->entry);

       if (ret == (ARCHIVE_EOF))

       {

         rar->has_endarc_header = 1;

         ret = archive_read_format_rar_read_header(a, a->entry);

       }

+      rar->filename_must_match = 0;

       if (ret != (ARCHIVE_OK))

         return NULL;

       return rar_read_ahead(a, min, avail);

-- 

2.17.1