initramfs: fix initramfs to work with hardlinked init

Change cb6ff208076b5f434db1b8c983429269d719cef5 ("NOMMU: Support XIP on
initramfs") seems to have broken booting from initramfs with /sbin/init
being a hardlink.

It seems like the logic required for XIP on nommu, i.e.  ftruncate to
reported cpio header file size (body_len) is broken for hardlinks, which
have a reported size of 0, and the truncate thus nukes the contents of the
file (in my case busybox), making boot impossible and ending with runaway
loop modprobe binfmt-0000 - and of course 0000 is not a valid binary
format.

My fix is to only call ftruncate if size is non-zero which fixes things
for me, but I'm not certain whether this will break XIP for those files on
nommu systems, although I would guess not.

Signed-off-by: Randy Robertson <rmrobert@vmware.com>
Acked-by: David Howells <dhowells@redhat.com>
Acked-by: Paul Mundt <lethal@linux-sh.org>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/init/initramfs.c b/init/initramfs.c
index e44f2d932cc4..9ee7b7810417 100644
--- a/init/initramfs.c
+++ b/init/initramfs.c
@@ -310,7 +310,8 @@ static int __init do_name(void)
                         if (wfd >= 0) {
                                 sys_fchown(wfd, uid, gid);
                                 sys_fchmod(wfd, mode);
-                                sys_ftruncate(wfd, body_len);
+                                if (body_len)
+                                        sys_ftruncate(wfd, body_len);
                                 vcollected = kstrdup(collected, GFP_KERNEL);
                                 state = CopyFile;
                         }