Fix for shared flat binary format in 2.6.30

[Bernd Schmidt <bernds_cb1@t-online.de>]

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This fixes a crash in 2.6.30 with shared flat binaries.  prepare_binfmt 
now requires a cred pointer to be set up, which isn't done in binfmt_flat.c.

Signed-off-by: Bernd Schmidt <bernds_cb1@t-online.de>
Acked-by: David Howells <dhowells@redhat.com>
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Index: fs/binfmt_flat.c
===================================================================
--- fs/binfmt_flat.c	(revision 6766)
+++ fs/binfmt_flat.c	(working copy)
@@ -853,14 +853,23 @@ static int load_flat_shared_library(int 
 	/* Open the file up */
 	bprm.filename = buf;
 	bprm.file = open_exec(bprm.filename);
+	bprm.cred = NULL;
 	res = PTR_ERR(bprm.file);
 	if (IS_ERR(bprm.file))
 		return res;
 
+	bprm.cred = prepare_exec_creds();
+	if (!bprm.cred)
+		goto out;
+
 	res = prepare_binprm(&bprm);
 
 	if (res <= (unsigned long)-4096)
 		res = load_flat_file(&bprm, libs, id, NULL, NULL);
+out:
+	if (bprm.cred)
+		abort_creds (bprm.cred);
+
 	if (bprm.file) {
 		allow_write_access(bprm.file);
 		fput(bprm.file);