a new function dup_shell() to replace ok_shell() and make it unconditionnally
strdup() its result to make the caller's code simplier. Change ok_shell() to
just return an integer value suitable for tests (it was used mainly for that
purpose). Do not use strdup() in the caller's code but rely on dup_shell()
that will do the job for us.
PR: bin/2442
1) Fix up vendor IDs for files I'm touching and put FBSDID in the right place.
2) Cast return value of snprintf to size_t rather than casting sizeof() to
an int, 'cos we know snprintf returns a non-genative number.
3) Avoid 'char *blank = "";' by just strduping. This could be bad sometimes,
but all these variables usually point at malloced memory so this makes
them always point at malloced memory.
shell to one of the following:
- a non-existent file
- a non-regular file
- a file without any execute bits set
The shell is still set to whatever they entered even if the above
conditions exist (hey, it is the super user doing this after all :-),
but this might give the admin. some warning that they are about to screw
themselves and give them a chance to fix it before it is too late.
Inspired by: some new FreeBSD user on USENET who set his root shell
to a shell that doesn't exist and now can't gain access to root (don't
worry, I sent him some mail on how to recover from this).
