On Sun, 15 Sep 2013 14:33:53 +0530 (IST) P J P <ppan...@redhat.com> wrote:
> 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 how 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 <pra...@redhat.com>
>
> diff --git a/init/do_mounts_rd.c b/init/do_mounts_rd.c
> index 6be2879..76faec1 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)
> + {
> + printk(KERN_EMERG "Invalid decompression routine address: %p\n",
> deco);
> + panic("Could not decompress initial ramdisk image.");
> + }
A few things here.
- the coding style is very unconventional. We'd do it like this:
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 address: %p\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;
return result;
}
- Note the use of the pr_emerg() shorthand, which prevents the
statement from overflowing 80 columns.
- There isn't much point in printing the value of `deco' - we already
know it's NULL. Isn't there some more useful message we can display
which will tell the user what he/she did wrong, and which explains
how to fix it?
- Is anyone working on fixing up Kconfig/dracut(8) so the correct
decompression method is used?
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