modules: Fix corruption of /proc/kallsyms

modules: Fix corruption of /proc/kallsyms

The commit 91fb02f31505 ("module: Move kallsyms support into a separate
file") changed from using strlcpy() to using strscpy() which created a
buffer overflow. That happened because:
 1) an incorrect value was passed as the buffer length
 2) strscpy() (unlike strlcpy()) may copy beyond the length of the
    input string when copying word-by-word.
The assumption was that because it was already known that the strings
being copied would fit in the space available, it was not necessary
to correctly set the buffer length.  strscpy() breaks that assumption
because although it will not touch bytes beyond the given buffer length
it may write bytes beyond the input string length when writing
word-by-word.

The result of the buffer overflow is to corrupt the symbol type
information that follows. e.g.

 $ sudo cat -v /proc/kallsyms | grep '\^' | head
 ffffffffc0615000 ^@ rfcomm_session_get  [rfcomm]
 ffffffffc061c060 ^@ session_list        [rfcomm]
 ffffffffc06150d0 ^@ rfcomm_send_frame   [rfcomm]
 ffffffffc0615130 ^@ rfcomm_make_uih     [rfcomm]
 ffffffffc07ed58d ^@ bnep_exit   [bnep]
 ffffffffc07ec000 ^@ bnep_rx_control     [bnep]
 ffffffffc07ec1a0 ^@ bnep_session        [bnep]
 ffffffffc07e7000 ^@ input_leds_event    [input_leds]
 ffffffffc07e9000 ^@ input_leds_handler  [input_leds]
 ffffffffc07e7010 ^@ input_leds_disconnect       [input_leds]

Notably, the null bytes (represented above by ^@) can confuse tools.

Fix by correcting the buffer length.

Fixes: 91fb02f31505 ("module: Move kallsyms support into a separate file")
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>