Critical: fix inverted logic here

strcmp(str, "") returns 0 (false) when str is empty, meaning the check is
inverted: it returns NULL when parsing succeeds and continues when parsing
fails. This allows non-numeric strings to pass through as array indices, leading
to type confusion and potentially incorrect memory access.

The strcmp logic handles most cases correctly (non-numeric strings return NULL,
valid integers pass through). However, the empty string "" is accepted as a
valid array index of 0: [10, 20, 30] #> '[""]' returns 10 instead of NULL. This
occurs because strtol("") sets lindex=0 and str="", so strcmp("", "") returns 0,
bypassing the error check.

Signed-off-by: David Christensen <[email protected]>

Author: sfc-gh-dachristensen

src/backend/utils/adt/agtype_ops.c

@@ -2098,7 +2098,7 @@ static Datum get_agtype_path_all(FunctionCallInfo fcinfo, bool as_text)
                 char* str = NULL;
                 lindex = strtol(cur_key->val.string.val, &str, 10);
 
-                if (strcmp(str, ""))
+                if (strcmp(str, "") != 0)
                 {
                     PG_RETURN_NULL();
                 }