transport-helper: avoid reading past end-of-string

We detect the "import-marks" capability by looking for that
string, but _without_ a trailing space. Then we skip past it
using strlen("import-marks "), with a space. So if a remote
helper gives us exactly "import-marks", we will read past
the end-of-string by one character.

This is unlikely to be a problem in practice, because such
input is malformed in the first place, and because there is
a good chance that the string has an extra NUL terminator
one character after the original (because it formerly had a
newline in it that we parsed off).

We can fix it by using skip_prefix with "import-marks ",
with the space. The other form appears to be a typo from
a515ebe (transport-helper: implement marks location as
capability, 2011-07-16); "import-marks" has never existed
without an argument, and it should match the "export-marks"
definition above.

Speaking of which, we can also use skip_prefix in a few
other places while we are in the function.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/transport-helper.c b/transport-helper.c
index 84c616f180bebc730d05f306906558dd0abad2a4..3d8fe7d801293a338f13dfd01ba352e84c658813 100644 (file)
--- a/transport-helper.c
+++ b/transport-helper.c
@@ -153,7 +153,7 @@ static struct child_process *get_helper(struct transport *transport)
        write_constant(helper->in, "capabilities\n");
 
        while (1) {
-               const char *capname;
+               const char *capname, *arg;
                int mandatory = 0;
                if (recvline(data, &buf))
                        exit(128);
@@ -183,19 +183,19 @@ static struct child_process *get_helper(struct transport *transport)
                        data->export = 1;
                else if (!strcmp(capname, "check-connectivity"))
                        data->check_connectivity = 1;
-               else if (!data->refspecs && starts_with(capname, "refspec ")) {
+               else if (!data->refspecs && skip_prefix(capname, "refspec ", &arg)) {
                        ALLOC_GROW(refspecs,
                                   refspec_nr + 1,
                                   refspec_alloc);
-                       refspecs[refspec_nr++] = xstrdup(capname + strlen("refspec "));
+                       refspecs[refspec_nr++] = xstrdup(arg);
                } else if (!strcmp(capname, "connect")) {
                        data->connect = 1;
                } else if (!strcmp(capname, "signed-tags")) {
                        data->signed_tags = 1;
-               } else if (starts_with(capname, "export-marks ")) {
-                       data->export_marks = xstrdup(capname + strlen("export-marks "));
-               } else if (starts_with(capname, "import-marks")) {
-                       data->import_marks = xstrdup(capname + strlen("import-marks "));
+               } else if (skip_prefix(capname, "export-marks ", &arg)) {
+                       data->export_marks = xstrdup(arg);
+               } else if (skip_prefix(capname, "import-marks ", &arg)) {
+                       data->import_marks = xstrdup(arg);
                } else if (starts_with(capname, "no-private-update")) {
                        data->no_private_update = 1;
                } else if (mandatory) {