From: Gerd Knorr <kraxel@bytesex.org>, and me, Paolo Giarrusso

This is a rewrite of the mconsole_proc function.

The old code had the problem that the kernel crashed after calling
"uml_mconsole proc <somefile>" a few times.  I havn't tracked what exactly
causes the problem, I guess trying to access the procfs without actually
mounting it somewhere causes some corruption of kernel data structures.

The new code simply openes /proc/<file> via sys_open().  That simplifies the
function alot.  It also doesn't crash any more ;)

Also, from Paolo Giarrusso: When printing the content of a file through the
"proc" command, make it begin on his own line.

PROBLEMS:

Drawback is that it only works when procfs is actually mounted below /proc.
And within UML, often this is false, because when building honeypots we mount
HPPFS under /proc to avoid the hacker recognizing he's attacking a UML
instance.

One suggestion I've received to fix the later issue was to mount the procfs
within a kernel thread with a private namespace, but I havn't tried that so
far.

Instead, we'd like to fix the actual code of the mconsole_proc function.  From
"Anthony Brock" Anthony_Brock (at) ous (dot) edu comes a comment, suggesting
where the bug lays (as noted in the source): removing part of the code (it
seems the symlink lookup) there are no more crashes.
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade_spam@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>