Re: [Bug-tar] [BUG] [PATCH] Multiple Bug Reports for an Old GNU tar Bug

[Paul Eggert]

On 10/27/2010 03:19 AM, Shlomi Fish wrote:

> This bug was originally reported on
> http://www.mail-archive.com/address@hidden/msg02601.html (and a patch was 
> provided)

Thanks, I didn't see that.  That patch doesn't completely fix the bug,
in the sense that it does not completely fix the technical violation
of the C Standard that GCC only partly detects.

I installed the following patch instead, which I think does fix the
technical violation in question.  Could you please give it a try
on your platform?  Thanks.


>From c7539fe7236f1cc1658fab56c427850712c141ea Mon Sep 17 00:00:00 2001
From: Paul Eggert <address@hidden>
Date: Wed, 27 Oct 2010 22:25:18 -0700
Subject: [PATCH] tar: don't cross struct member boundaries with OLDGNU_MAGIC

* src/create.c (write_gnu_long_link, start_header): Access
header->buffer + offsetof (struct posix_header, magic), instead of
header->header.magic, when reading or writing the OLDGNU_MAGIC
pattern.  The code violates the C standard without this change,
and GCC warns about this if fortify checking is enabled.  It's not
a bug on traditional (i.e., non-debugging) platforms, but it does
violate the C standard so it should be fixed.  Problem originally
reported by John Emil Karlson in
<http://lists.gnu.org/archive/html/bug-tar/2010-04/msg00023.html>.
* src/list.c (decode_header): Likewise.
---
 src/create.c |    6 ++++--
 src/list.c   |    6 ++++--
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/create.c b/src/create.c
index 05af0d9..a1e90a3 100644
--- a/src/create.c
+++ b/src/create.c
@@ -562,7 +562,8 @@ write_gnu_long_link (struct tar_stat_info *st, const char 
*p, char type)
   GNAME_TO_CHARS (tmpname, header->header.gname);
   free (tmpname);
 
-  strcpy (header->header.magic, OLDGNU_MAGIC);
+  strcpy (header->buffer + offsetof (struct posix_header, magic),
+         OLDGNU_MAGIC);
   header->header.typeflag = type;
   finish_header (st, header, -1);
 
@@ -899,7 +900,8 @@ start_header (struct tar_stat_info *st)
     case OLDGNU_FORMAT:
     case GNU_FORMAT:   /*FIXME?*/
       /* Overwrite header->header.magic and header.version in one blow.  */
-      strcpy (header->header.magic, OLDGNU_MAGIC);
+      strcpy (header->buffer + offsetof (struct posix_header, magic),
+             OLDGNU_MAGIC);
       break;
 
     case POSIX_FORMAT:
diff --git a/src/list.c b/src/list.c
index c65e171..a70f0d3 100644
--- a/src/list.c
+++ b/src/list.c
@@ -122,7 +122,7 @@ transform_stat_info (int typeflag, struct tar_stat_info 
*stat_info)
   if (typeflag == GNUTYPE_VOLHDR)
     /* Name transformations don't apply to volume headers. */
     return;
-  
+
   transform_member_name (&stat_info->file_name, XFORM_REGFILE);
   switch (typeflag)
     {
@@ -592,7 +592,9 @@ decode_header (union block *header, struct tar_stat_info 
*stat_info,
       else
        format = USTAR_FORMAT;
     }
-  else if (strcmp (header->header.magic, OLDGNU_MAGIC) == 0)
+  else if (strcmp (header->buffer + offsetof (struct posix_header, magic),
+                  OLDGNU_MAGIC)
+          == 0)
     format = hbits ? OLDGNU_FORMAT : GNU_FORMAT;
   else
     format = V7_FORMAT;
-- 
1.7.2