Hello,

While building the 3.11 kernel recently, I bumped into this issue.

Menuconfig allows one to choose compression format of an initial ramdisk 
image. If we select any compression other than the default gzip(1), it leads 
to a NULL pointer dereference while loading the initramfs image, at boot up.

Because - $ make install - does not pass on the selected compression format to 
dracut(8) tool, it generates the initramfs file compressed with the default 
gzip(1) format. But the kernel knows only to decompress the chosen format.

The attached patch herein, replaces the crash by an explicit panic() call with 
an appropriate error message. It keeps the kernel from eventually panicking in 
init/do_mounts.c: mount_root_block() with an inaccurate error message and 
which also looses the earlier printk output that hints about the missing 
gzip(1) decompression support.
   -> panic("VFS: Unable to mount root fs on %s", b);

Could someone please review this patch?

Thank you.
--
Prasad J Pandit / Red Hat Security Response Team
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