PR23254, ld.bfd mishandles file pointers while scanning archive

Best practice is to not mix lseek/read with fseek/fread on the same
underlying file descriptor, as not all stdio implementations will cope.
Since the plugin uses lseek/read while bfd uses fseek/fread this patch
reopens the file for exclusive use by the plugin rather than trying to
restore the file descriptor.  That allows the plugin to read the file
after plugin_call_claim_file too.

bfd/
	PR 23254
	* plugin.c (bfd_plugin_open_input): Allow for possibility of
	nested archives.  Open file again for plugin.
	(try_claim): Don't save and restore file position.  Close file
	if not claimed.
	* sysdep.h (O_BINARY): Define.
ld/
	PR 23254
	* plugin.c (plugin_call_claim_file): Revert 2016-07-19 patch.
	(plugin_object_p): Don't dup file descriptor.

1 files changed, 14 insertions, 6 deletions

diff --git a/bfd/plugin.c b/bfd/plugin.c
index 16a706a..7c5bba2 100644
--- a/bfd/plugin.c
+++ b/bfd/plugin.c
@@ -166,14 +166,22 @@ bfd_plugin_open_input (bfd *ibfd, struct ld_plugin_input_file *file)
   bfd *iobfd;
 
   iobfd = ibfd;
-  if (ibfd->my_archive && !bfd_is_thin_archive (ibfd->my_archive))
-    iobfd = ibfd->my_archive;
+  while (iobfd->my_archive
+	 && !bfd_is_thin_archive (iobfd->my_archive))
+    iobfd = iobfd->my_archive;
   file->name = iobfd->filename;
 
   if (!iobfd->iostream && !bfd_open_file (iobfd))
     return 0;
 
-  file->fd = fileno ((FILE *) iobfd->iostream);
+  /* The plugin API expects that the file descriptor won't be closed
+     and reused as done by the bfd file cache.  So open it again.
+     dup isn't good enough.  plugin IO uses lseek/read while BFD uses
+     fseek/fread.  It isn't wise to mix the unistd and stdio calls on
+     the same underlying file descriptor.  */
+  file->fd = open (file->name, O_RDONLY | O_BINARY);
+  if (file->fd < 0)
+    return 0;
 
   if (iobfd == ibfd)
     {
@@ -197,12 +205,12 @@ try_claim (bfd *abfd)
   int claimed = 0;
   struct ld_plugin_input_file file;
 
+  file.handle = abfd;
   if (!bfd_plugin_open_input (abfd, &file))
     return 0;
-  file.handle = abfd;
-  off_t cur_offset = lseek (file.fd, 0, SEEK_CUR);
   claim_file (&file, &claimed);
-  lseek (file.fd, cur_offset, SEEK_SET);
+  if (!claimed)
+    close (file.fd);
   return claimed;
 }