Add a hook to enable load-time inspection of program headers

This hook can be used to perform additional compatibility checks
between shared libraries by inspecting custom program header
information.

	* elf/dl-machine-reject-phdr.h: New file.
	* elf/dl-load.c: #include that.
	(open_verify): Call elf_machine_reject_phdr_p and ignore the file
	if that returned true.

2 files changed, 40 insertions, 0 deletions

diff --git a/elf/dl-load.c b/elf/dl-load.c
index ce5b626b26..7a03ccfd2a 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -41,6 +41,7 @@
 #include <dl-load.h>
 #include <dl-map-segments.h>
 #include <dl-unmap-segments.h>
+#include <dl-machine-reject-phdr.h>
 
 
 #include <endian.h>
@@ -1683,6 +1684,11 @@ open_verify (const char *name, struct filebuf *fbp, struct link_map *loader,
 	    }
 	}
 
+      if (__glibc_unlikely (elf_machine_reject_phdr_p
+			    (phdr, ehdr->e_phnum, fbp->buf, fbp->len,
+			     loader, fd)))
+	goto close_and_out;
+
       /* Check .note.ABI-tag if present.  */
       for (ph = phdr; ph < &phdr[ehdr->e_phnum]; ++ph)
 	if (ph->p_type == PT_NOTE && ph->p_filesz >= 32 && ph->p_align >= 4)
diff --git a/elf/dl-machine-reject-phdr.h b/elf/dl-machine-reject-phdr.h
new file mode 100644
index 0000000000..d110a32023
--- /dev/null
+++ b/elf/dl-machine-reject-phdr.h
@@ -0,0 +1,34 @@
+/* Machine-dependent program header inspection for the ELF loader.
+   Copyright (C) 2014 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _DL_MACHINE_REJECT_PHDR_H
+#define _DL_MACHINE_REJECT_PHDR_H 1
+
+#include <stdbool.h>
+
+/* Return true iff ELF program headers are incompatible with the running
+   host.  */
+static inline bool
+elf_machine_reject_phdr_p (const ElfW(Phdr) *phdr, uint_fast16_t phnum,
+			   const char *buf, size_t len, struct link_map *map,
+			   int fd)
+{
+  return false;
+}
+
+#endif /* dl-machine-reject-phdr.h */