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Re: Vulnerability Report: Heap-Buffer-Overflow on Sharutils (unshar) 4.15.2

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The bellow patch should fix it. I don't know if sharutils author prefers
reading up to a memory page size or an I/O buffer size.


>From 1067cdba6d08f2a765cb0ea371189a5b703eb4db Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Petr=20P=C3=ADsa=C5=99?= <ppisar@redhat.com>
Date: Thu, 22 Feb 2018 16:39:43 +0100
Subject: [PATCH] Fix a heap-buffer-overflow in find_archive()
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

rw_buffer has allocated rw_base_size bytes. But subsequend fgets() in
find_archive() reads up-to BUFSIZ bytes.

On my system, BUFSIZ is 8192. rw_base_size is usually equaled to
a memory page size, 4096 on my system. Thus find_archive() can write
beyonded allocated memmory for rw_buffer array:

$ valgrind -- ./unshar /tmp/id\:000000\,sig\:06\,src\:000005+000030\,op\:splice\,rep\:4
==30582== Memcheck, a memory error detector
==30582== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==30582== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==30582== Command: ./unshar /tmp/id:000000,sig:06,src:000005+000030,op:splice,rep:4
==30582==
==30582== Invalid write of size 1
==30582==    at 0x4EAB480: _IO_getline_info (in /usr/lib64/libc-2.27.so)
==30582==    by 0x4EB47C2: fgets_unlocked (in /usr/lib64/libc-2.27.so)
==30582==    by 0x10BF60: fgets_unlocked (stdio2.h:320)
==30582==    by 0x10BF60: find_archive (unshar.c:243)
==30582==    by 0x10BF60: unshar_file (unshar.c:379)
==30582==    by 0x10BCCC: validate_fname (unshar-opts.c:604)
==30582==    by 0x10BCCC: main (unshar-opts.c:639)
==30582==  Address 0x523a790 is 0 bytes after a block of size 4,096 alloc'd
==30582==    at 0x4C2DBBB: malloc (vg_replace_malloc.c:299)
==30582==    by 0x10C670: init_unshar (unshar.c:450)
==30582==    by 0x10BC55: main (unshar-opts.c:630)

This was reported in
<http://lists.gnu.org/archive/html/bug-gnu-utils/2018-02/msg00004.html>.

Signed-off-by: Petr Písař <ppisar@redhat.com>
---
 src/unshar.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/unshar.c b/src/unshar.c
index 80bc3a9..0fc3773 100644
--- a/src/unshar.c
+++ b/src/unshar.c
@@ -240,7 +240,7 @@ find_archive (char const * name, FILE * file, off_t start)
       off_t position = ftello (file);
 
       /* Read next line, fail if no more and no previous process.  */
-      if (!fgets (rw_buffer, BUFSIZ, file))
+      if (!fgets (rw_buffer, rw_base_size, file))
 	{
 	  if (!start)
 	    error (0, 0, _("Found no shell commands in %s"), name);
-- 
2.13.6

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Re: Vulnerability Report: Heap-Buffer-Overflow on Sharutils (unshar) 4.15.2 Petr Pisar <ppisar@redhat.com> - 2018-02-22 15:56 +0000

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