[glibc] localedef: check magic value on archive load [BZ #28650]

[Aurelien Jarno <aurel32@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=cbab7f726877badc5059316e7248be7c3bff9d96

commit cbab7f726877badc5059316e7248be7c3bff9d96
Author: Aurelien Jarno <aurelien@aurel32.net>
Date:   Sun Dec 5 11:51:17 2021 +0100

    localedef: check magic value on archive load [BZ #28650]
    
    localedef currently blindly trust the archive header. When passed an
    archive file with the wrong endianess, this leads to a segmentation
    fault:
    
      $ localedef --big-endian --list-archive /usr/lib/locale/locale-archive
      Segmentation fault (core dumped)
    
    When passed non-archive files, asserts are reported on the best case,
    but sometimes it can lead to a segmentation fault:
    
      $ localedef --list-archive /bin/true
      localedef: programs/locarchive.c:1643: show_archive_content: Assertion `used < GET (head->namehash_used)' failed.
      Aborted (core dumped)
    
      $ localedef --list-archive /usr/lib/locale/C.utf8/LC_COLLATE
      Segmentation fault (core dumped)
    
    This patch improves the user experience by looking at the magic value,
    which is always written, but never checked. It should still be possible
    to trigger a segmentation fault with crafted files, but this already
    catch many cases.

Diff:
---
 locale/programs/locarchive.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/locale/programs/locarchive.c b/locale/programs/locarchive.c
index eeec3ab648..477499bd40 100644
--- a/locale/programs/locarchive.c
+++ b/locale/programs/locarchive.c
@@ -654,6 +654,13 @@ open_archive (struct locarhandle *ah, bool readonly)
       error (EXIT_FAILURE, errno, _("cannot read archive header"));
     }
 
+  /* Check the magic value */
+  if (GET (head.magic) != AR_MAGIC)
+    {
+      (void) lockf64 (fd, F_ULOCK, sizeof (struct locarhead));
+      error (EXIT_FAILURE, 0, _("bad magic value in archive header"));
+    }
+
   ah->fd = fd;
   ah->mmaped = st.st_size;