[Bug-tar] [PATCH] --one-top-level: avoid a heap-buffer-overflow

[Jim Meyering]

I configured as usual, then ran ASAN-enabled tests like this:

  make CFLAGS='-O0 -ggdb3' AM_CFLAGS=-fsanitize=address \
    AM_LDFLAGS='-fsanitize=address -static-libasan' check \
    TESTSUITEFLAGS=--jobs=40

That exposed a buffer-overrun bug.
Here's a stand-alone reproducer using valgrind:

  $ : > k && tar cf k.tar k; valgrind tar --one-top-level -tf k.tar

  Invalid read of size 1
     at 0x421FCF: strip_compression_suffix (suffix.c:107)
     by 0x405903: decode_options (tar.c:2545)
     by 0x405903: main (tar.c:2708)
   Address 0x5ecfb6d is 3 bytes before a block of size 6 alloc'd
     at 0x4C2CB6B: malloc (vg_replace_malloc.c:299)
     by 0x52F07B9: strndup (strndup.c:43)
     by 0x441948: xstrndup (xstrndup.c:32)
     by 0x4058F8: decode_options (tar.c:2544)
     by 0x4058F8: main (tar.c:2708)


>From e68608dd3ae21fbdb24caeddc2bba34c265f53b7 Mon Sep 17 00:00:00 2001
From: Jim Meyering <address@hidden>
Date: Sat, 7 Apr 2018 08:41:46 -0700
Subject: [PATCH] --one-top-level: avoid a heap-buffer-overflow

* NEWS: Mention this.
* src/suffix.c (strip_compression_suffix): Fix computation
of result string length.  Also rename the now-outer "len"
to "base_len" to make clear it is the suffix-trimmed length.
Without this change, some ASAN-enabled test runs would fail
with this:

==30815==ERROR: AddressSanitizer: heap-buffer-overflow on address 
0x6020000002ed at pc 0x00000049d1f4 bp 0x7ffeb5906d50 sp 0x7ffeb5906500
READ of size 1 at 0x6020000002ed thread T0
    #0 0x49d1f3 in __interceptor_strncmp 
/j/gcc/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc:407
    #1 0x5670f3 in strip_compression_suffix /j/tar/src/suffix.c:107
    #2 0x575788 in decode_options /j/tar/src/tar.c:2545
    #3 0x5760c0 in main /j/tar/src/tar.c:2708
    #4 0x7f105090df29 in __libc_start_main ../csu/libc-start.c:308
    #5 0x408629 in _start (/j/tar/src/tar+0x408629)

0x6020000002ed is located 3 bytes to the left of 6-byte region 
[0x6020000002f0,0x6020000002f6)
allocated by thread T0 here:
    #0 0x4d0710 in __interceptor_malloc 
/j/gcc/libsanitizer/asan/asan_malloc_linux.cc:86
    #1 0x4908ad in __interceptor_strndup 
/j/gcc/libsanitizer/sanitizer_common/sanitizer_common_interceptors.inc:326
    #2 0x5cbcbd in xstrndup /j/tar/gnu/xstrndup.c:32
    #3 0x5a325b in base_name /j/tar/gnu/basename.c:57
    #4 0x575772 in decode_options /j/tar/src/tar.c:2544
    #5 0x5760c0 in main /j/tar/src/tar.c:2708
    #6 0x7f105090df29 in __libc_start_main ../csu/libc-start.c:308
---
 NEWS         |  7 +++++--
 src/suffix.c | 11 +++++------
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/NEWS b/NEWS
index 998258e..ee607ed 100644
--- a/NEWS
+++ b/NEWS
@@ -1,9 +1,12 @@
-GNU tar NEWS - User visible changes. 2018-03-18
+GNU tar NEWS - User visible changes. 2018-04-07
 Please send GNU tar bug reports to <address@hidden>

 
 version 1.30.90 (Git)

+* Fix heap-buffer-overrun with --one-top-level.
+Bug introduced with the addition of that option in 1.28.
+
 * Support for zstd compression

 New option '--zstd' instructs tar to use zstd as compression program.
@@ -53,7 +56,7 @@ causing subsequent link extractions in that directory to fail.

 This new warning control option suppresses warning messages about
 unreadable files and directories. It has effect only if used together
-with the --ignore-failed-read option.  
+with the --ignore-failed-read option.

 * The --warnings=none option now suppresses all warnings

diff --git a/src/suffix.c b/src/suffix.c
index 66b5694..72872b0 100644
--- a/src/suffix.c
+++ b/src/suffix.c
@@ -62,7 +62,7 @@ find_compression_suffix (const char *name, size_t *ret_len)
     {
       size_t len;
       struct compression_suffix *p;
-      
+
       suf++;
       len = strlen (suf);

@@ -100,12 +100,12 @@ char *
 strip_compression_suffix (const char *name)
 {
   char *s = NULL;
-  size_t len;
+  size_t base_len;

-  if (find_compression_suffix (name, &len))
+  if (find_compression_suffix (name, &base_len))
     {
-      if (strncmp (name + len - 4, ".tar", 4) == 0)
-       len -= 4;
+      size_t len = (strncmp (name + base_len, ".tar", 4) == 0
+                   ? base_len : strlen (name));
       if (len == 0)
        return NULL;
       s = xmalloc (len + 1);
@@ -114,4 +114,3 @@ strip_compression_suffix (const char *name)
     }
   return s;
 }
-  
-- 
2.17.0