cifs: return ENAMETOOLONG for overlong names in cifs_open()/cifs_lookup()

cifs: return ENAMETOOLONG for overlong names in cifs_open()/cifs_lookup()

commit d3edede29f74d335f81d95a4588f5f136a9f7dcf upstream.

Add checking for the path component length and verify it is <= the maximum
that the server advertizes via FileFsAttributeInformation.

With this patch cifs.ko will now return ENAMETOOLONG instead of ENOENT
when users to access an overlong path.

To test this, try to cd into a (non-existing) directory on a CIFS share
that has a too long name:
cd /mnt/aaaaaaaaaaaaaaa...

and it now should show a good error message from the shell:
bash: cd: /mnt/aaaaaaaaaaaaaaaa...aaaaaa: File name too long

rh bz 1153996

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>
[bwh: Backported to 3.2: name checks are done only in cifs_lookup()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>