scanner: fix out-of-bound memory write in include_file()

scanner: fix out-of-bound memory write in include_file()

Before patch:
 # echo 'include "/tmp/rules.nft"' > /tmp/rules.nft
 # nft -f /tmp/rules.nft
 In file included from /tmp/rules.nft:1:1-25:
                  from /tmp/rules.nft:1:1-25:
 [snip]
                  from /tmp/rules.nft:1:1-25:
 /tmp/rules.nft:1:1-25: Error: Include nested too deeply, max 16 levels
 include "/tmp/rules.nft"
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 double free or corruption (out)
 Aborted (core dumped)

valgrind reports:

==8856== Invalid write of size 8
==8856==    at 0x4E8FCAF: include_file (scanner.l:718)
==8856==    by 0x4E8FEF6: include_glob (scanner.l:793)
==8856==    by 0x4E9985D: scanner_include_file (scanner.l:875)
==8856==    by 0x4E89D7A: nft_parse (parser_bison.y:828)
==8856==    by 0x4E765E1: nft_parse_bison_filename (libnftables.c:394)
==8856==    by 0x4E765E1: nft_run_cmd_from_filename (libnftables.c:497)
==8856==    by 0x40172D: main (main.c:340)

So perform bounds checking on MAX_INCLUDE_DEPTH before writing.

After patch:
 # nft -f /tmp/rules.nft
 In file included from /tmp/rules.nft:1:1-25:
                  from /tmp/rules.nft:1:1-25:
 [snip]
                  from /tmp/rules.nft:1:1-25:
 /tmp/rules.nft:1:1-25: Error: Include nested too deeply, max 16 levels
 include "/tmp/rules.nft"
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 # echo $?
 1

Also:
Update scanner_push_file() function definition accordingly.

Fixes: 32325e3c3fab4 ("libnftables: Store top_scope in struct nft_ctx")
Signed-off-by: Eric Jallot <ejallot@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>