vty: fix use-after-free and memleaks in is_cmd_ambiguous()
vty_test: add test against ambiguous cmd causing use-after-free and memory
leaks. Add this test along with the fix, because the new test triggers the
memory use-after-free and leaks, causing build failures.
Add cmd_deopt_with_ctx() to allow passing a specific talloc ctx.
is_cmd_ambiguous(): keep all cmd_deopt() allocations until the function exits.
Add a comment explaining why. Before this, if a command matched an optional
"[arg]" with square brackets, we would keep it in local var 'matched', but we
would free the string it points to at the end of that loop iteration; upon
encountering another match, we would attempt to strcmp against the freed
'matched'. Instead of adding hard-to-read and -verify free/alloc dances to keep
the 'matched' accurately freed/non-freed/..., just keep all cmd_deopt() string
allocated until done.
Needless to say that this should have been implemented on a lower level upon
inventing optional args, but at least this is fixing a program crash.
Related: OS#33903390
Change-Id: Ia71ba742108b5ff020997bfb612ad5eb30d04fcd
diff --git a/src/vty/command.c b/src/vty/command.c
index 51dece3..43f974c 100644
--- a/src/vty/command.c
+++ b/src/vty/command.c
@@ -1304,8 +1304,7 @@
}
/* helper to retrieve the 'real' argument string from an optional argument */
-static char *
-cmd_deopt(const char *str)
+static char *cmd_deopt(void *ctx, const char *str)
{
/* we've got "[blah]". We want to strip off the []s and redo the
* match check for "blah"
@@ -1315,7 +1314,7 @@
if (len < 3)
return NULL;
- return talloc_strndup(tall_vty_cmd_ctx, str + 1, len - 2);
+ return talloc_strndup(ctx, str + 1, len - 2);
}
static enum match_type
@@ -1326,7 +1325,7 @@
if (recur && CMD_OPTION(str))
{
enum match_type ret;
- char *tmp = cmd_deopt(str);
+ char *tmp = cmd_deopt(tall_vty_cmd_ctx, str);
/* this would be a bug in a command, however handle it gracefully
* as it we only discover it if a user tries to run it
@@ -1475,6 +1474,7 @@
static int
is_cmd_ambiguous(char *command, vector v, int index, enum match_type type)
{
+ int ret = 0;
unsigned int i;
unsigned int j;
struct cmd_element *cmd_element;
@@ -1482,6 +1482,16 @@
vector descvec;
struct desc *desc;
+ /* In this loop, when a match is found, 'matched' points to it. If on a later iteration, an
+ * identical match is found, the command is ambiguous. The trickiness is that a string may be
+ * enclosed in '[str]' square brackets, which get removed by a talloc_strndup(), via cmd_deopt().
+ * Such a string is usually needed for one loop iteration, except when 'matched' points to it. In
+ * that case, the string must remain allocated until this function exits or another match comes
+ * around. This is sufficiently confusing to justify a separate talloc tree to store all of the
+ * odd allocations, and to free them all at the end. We are not expecting too many optional args
+ * or ambiguities to cause a noticeable memory footprint from keeping all allocations. */
+ void *cmd_deopt_ctx = NULL;
+
for (i = 0; i < vector_active(v); i++)
if ((cmd_element = vector_slot(v, i)) != NULL) {
int match = 0;
@@ -1493,9 +1503,15 @@
enum match_type ret;
const char *str = desc->cmd;
- if (CMD_OPTION(str))
- if ((str = cmd_deopt(str)) == NULL)
+ if (CMD_OPTION(str)) {
+ if (!cmd_deopt_ctx)
+ cmd_deopt_ctx =
+ talloc_named_const(tall_vty_cmd_ctx, 0,
+ __func__);
+ str = cmd_deopt(cmd_deopt_ctx, str);
+ if (str == NULL)
continue;
+ }
switch (type) {
case exact_match:
@@ -1509,9 +1525,10 @@
{
if (matched
&& strcmp(matched,
- str) != 0)
- return 1; /* There is ambiguous match. */
- else
+ str) != 0) {
+ ret = 1; /* There is ambiguous match. */
+ goto free_and_return;
+ } else
matched = str;
match++;
}
@@ -1521,9 +1538,10 @@
(str, command)) {
if (matched
&& strcmp(matched,
- str) != 0)
- return 1;
- else
+ str) != 0) {
+ ret = 1;
+ goto free_and_return;
+ } else
matched = str;
match++;
}
@@ -1537,8 +1555,10 @@
if ((ret =
cmd_ipv6_prefix_match
(command)) != no_match) {
- if (ret == partly_match)
- return 2; /* There is incomplete match. */
+ if (ret == partly_match) {
+ ret = 2; /* There is incomplete match. */
+ goto free_and_return;
+ }
match++;
}
@@ -1552,8 +1572,10 @@
if ((ret =
cmd_ipv4_prefix_match
(command)) != no_match) {
- if (ret == partly_match)
- return 2; /* There is incomplete match. */
+ if (ret == partly_match) {
+ ret = 2; /* There is incomplete match. */
+ goto free_and_return;
+ }
match++;
}
@@ -1566,14 +1588,15 @@
default:
break;
}
-
- if (CMD_OPTION(desc->cmd))
- talloc_free((void*)str);
}
if (!match)
vector_slot(v, i) = NULL;
}
- return 0;
+
+free_and_return:
+ if (cmd_deopt_ctx)
+ talloc_free(cmd_deopt_ctx);
+ return ret;
}
/* If src matches dst return dst string, otherwise return NULL */