From 842d328ba52cb53ec057b0703fbc8fbc2a2d6f1a Mon Sep 17 00:00:00 2001
From: P J P <prasad@redhat.com>
Date: Tue, 24 Sep 2013 23:59:21 +0530
Subject: [PATCH] Fix NULL pointer dereference while loading initramfs

Make menuconfig allows one to choose compression format of an
initial ramdisk image. But this choice does not result in duly
compressed initial ramdisk image. Because - $ make install - does
not pass on the selected compression choice to the dracut(8) tool,
which creates the initramfs file. dracut(8) generates the image
with the default compression, ie. gzip(1).

If a user chose any other compression instead of gzip(1), it leads
to a crash due to NULL pointer dereference in crd_load(), caused by
a NULL function pointer returned by the 'decompress_method()' routine.
Because the initramfs image is gzip(1) compressed, whereas the kernel
knows only to decompress the chosen format and not gzip(1).

This patch replaces the crash by an explicit panic() call with an
appropriate error message. This shall prevent the kernel from
eventually panicking in: init/do_mounts.c: mount_block_root() with
  -> panic("VFS: Unable to mount root fs on %s", b);

Signed-off-by: P J P <prasad@redhat.com>

diff --git a/init/do_mounts_rd.c b/init/do_mounts_rd.c
index 6be2879..bdaa345 100644
--- a/init/do_mounts_rd.c
+++ b/init/do_mounts_rd.c
@@ -342,6 +342,13 @@ static int __init crd_load(int in_fd, int out_fd, decompress_fn deco)
 	int result;
 	crd_infd = in_fd;
 	crd_outfd = out_fd;
+
+	if (!deco) {
+		pr_emerg("Invalid decompression routine: %p; "
+				 "Select appropriate config option.\n", deco);
+		panic("Could not decompress initial ramdisk image.");
+	}
+
 	result = deco(NULL, 0, compr_fill, compr_flush, NULL, NULL, error);
 	if (decompress_error)
 		result = 1;
-- 
1.8.3.1