[binutils-gdb] looping in bfd_mach_o_fat_openr_next_archived_file

[Alan Modra]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=8d783d5e1d60ec951368ceaf7f4bb8c241e4d3ee

commit 8d783d5e1d60ec951368ceaf7f4bb8c241e4d3ee
Author: Alan Modra <amodra@gmail.com>
Date:   Wed Sep 14 16:57:42 2022 +0930

    looping in bfd_mach_o_fat_openr_next_archived_file
    
    mach-o.c doesn't sanity check mach-o-fat archives, making it easy for
    fuzzers to create an archive with mach_o_fat_archentry headers that
    point to the same offset.  bfd_mach_o_fat_openr_next_archived_file
    uses the previous element offset to find its header, and thus the next
    element.  If two offsets are the same, any tool reading the archive
    will get stuck.  This patch rejects such archives, and any with
    overlapping elements.
    
            * mach-o.c (overlap_previous): New function.
            (bfd_mach_o_fat_archive_p): Sanity check that elements do not
            overlap each other or the file and archive headers.

Diff:
---
 bfd/mach-o.c | 27 +++++++++++++++++++++++----
 1 file changed, 23 insertions(+), 4 deletions(-)

diff --git a/bfd/mach-o.c b/bfd/mach-o.c
index eb325236454..acb35e7f0c6 100644
--- a/bfd/mach-o.c
+++ b/bfd/mach-o.c
@@ -5497,6 +5497,22 @@ typedef struct mach_o_fat_data_struct
   mach_o_fat_archentry *archentries;
 } mach_o_fat_data_struct;
 
+/* Check for overlapping archive elements.  Note that we can't allow
+   multiple elements at the same offset even if one is empty, because
+   bfd_mach_o_fat_openr_next_archived_file assume distinct offsets.  */
+static bool
+overlap_previous (const mach_o_fat_archentry *elt, unsigned long i)
+{
+  unsigned long j = i;
+  while (j-- != 0)
+    if (elt[i].offset == elt[j].offset
+	|| (elt[i].offset > elt[j].offset
+	    ? elt[i].offset - elt[j].offset < elt[j].size
+	    : elt[j].offset - elt[i].offset < elt[i].size))
+      return true;
+  return false;
+}
+
 bfd_cleanup
 bfd_mach_o_fat_archive_p (bfd *abfd)
 {
@@ -5545,10 +5561,13 @@ bfd_mach_o_fat_archive_p (bfd *abfd)
       adata->archentries[i].offset = bfd_getb32 (arch.offset);
       adata->archentries[i].size = bfd_getb32 (arch.size);
       adata->archentries[i].align = bfd_getb32 (arch.align);
-      if (filesize != 0
-	  && (adata->archentries[i].offset > filesize
-	      || (adata->archentries[i].size
-		  > filesize - adata->archentries[i].offset)))
+      if ((filesize != 0
+	   && (adata->archentries[i].offset > filesize
+	       || (adata->archentries[i].size
+		   > filesize - adata->archentries[i].offset)))
+	  || (adata->archentries[i].offset
+	      < sizeof (hdr) + adata->nfat_arch * sizeof (arch))
+	  || overlap_previous (adata->archentries, i))
 	{
 	  bfd_release (abfd, adata);
 	  bfd_set_error (bfd_error_malformed_archive);