xshared: Fix for memleak in option merging with ebtables

The crucial difference in ebtables is that all extensions are loaded up
front instead of while parsing -m/-j flags. Since this loading of all
extensions before every call to do_parse() is pointless overhead (cf.
ebtables-restore), other tools' mechanism of freeing all merged options
in xtables_free_opts() after handling each command and resetting
xt_params->opts at the start of the parser loop is problematic.

Fixed commit entailed a hack to defeat the xt_params->opts happening at
start of do_parse() by assigning to xt_params->orig_opts after loading
all extensions. This approach caused a memleak though since
xtables_free_opts() called from xtables_merge_options() will free the
opts pointer only if it differs from orig_opts.

Resolve this via a different approach which eliminates the
xt_params->opts reset at the start of do_parse():

Make xt_params->opts be NULL until the first extension is loaded. Option
merging in command_match() and command_jump() tolerates a NULL pointer
there after minimal adjustment. Deinit in xtables_free_opts() is already
fine as it (re)turns xt_params->opts to a NULL pointer. With do_parse()
expecting that and falling back to xt_params->orig_opts, no explicit
initialization is required anymore and thus ebtables' init is not
mangled by accident.

A critical part is that do_parse() checks xt_params->opts pointer upon
each call to getopt_long() as it may get assigned while parsing.

Fixes: 58d364c7120b5 ("ebtables: Use do_parse() from xshared")
Signed-off-by: Phil Sutter <phil@nwl.cc>

1 files changed, 2 insertions, 4 deletions

diff --git a/libxtables/xtables.c b/libxtables/xtables.c
index 856bfae8..ae3ff25a 100644
--- a/libxtables/xtables.c
+++ b/libxtables/xtables.c
@@ -111,10 +111,8 @@ void basic_exit_err(enum xtables_exittype status, const char *msg, ...)
 
 void xtables_free_opts(int unused)
 {
-	if (xt_params->opts != xt_params->orig_opts) {
-		free(xt_params->opts);
-		xt_params->opts = NULL;
-	}
+	free(xt_params->opts);
+	xt_params->opts = NULL;
 }
 
 struct option *xtables_merge_options(struct option *orig_opts,