[PATCH v2 5/7] trace2: remove use of xstrfmt()

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <stolee@gmail.com>

We continue removing the possibility of a die() in the trace2 API by
banning xstrfmt(), which calls die() during a failure to format. Instead
of allowing a die(), perform a soft failure by failing to output the
trace2 data when such a failure occurs.

This requires carefully concatenating strings using memcpy() to
construct redacted data to avoid copying password information in traced
URLs.

Signed-off-by: Derrick Stolee <stolee@gmail.com>
---
 banned-die.h |  3 +++
 trace2.c     | 34 ++++++++++++++++++++++++++++++++--
 2 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/banned-die.h b/banned-die.h
index cb2eed75cd..14aecfdc7a 100644
--- a/banned-die.h
+++ b/banned-die.h
@@ -17,6 +17,9 @@
 #undef xstrdup
 #define xstrdup(str) BANNED(xstrdup)
 
+#undef xstrfmt
+#define xstrfmt(...) BANNED(xstrfmt)
+
 #undef ALLOC_ARRAY
 #define ALLOC_ARRAY(x, alloc) BANNED(ALLOC_ARRAY)
 
diff --git a/trace2.c b/trace2.c
index 7044276435..c37f783fa0 100644
--- a/trace2.c
+++ b/trace2.c
@@ -260,7 +260,10 @@ int trace2_is_enabled(void)
 static const char *redact_arg(const char *arg)
 {
 	const char *p, *colon;
+	const char *redact = ":<REDACTED>";
+	char *redacted;
 	size_t at;
+	size_t prefix_len, suffix_len, redacted_len, redact_len;
 
 	if (!trace2_redact ||
 	    (!skip_prefix(arg, "https://", &p) &&
@@ -275,7 +278,25 @@ static const char *redact_arg(const char *arg)
 	if (!colon)
 		return arg;
 
-	return xstrfmt("%.*s:<REDACTED>%s", (int)(colon - arg), arg, p + at);
+	redact_len = strlen(redact);
+	prefix_len = colon - arg;
+	suffix_len = strlen(p + at);
+
+	if (unsigned_add_overflows(prefix_len, suffix_len) ||
+	    unsigned_add_overflows(prefix_len + suffix_len, redact_len))
+		return NULL;
+
+	redacted_len = prefix_len + suffix_len + redact_len;
+
+	redacted = malloc(redacted_len);
+	if (!redacted)
+		return NULL;
+
+	memcpy(redacted, arg, prefix_len);
+	memcpy(redacted + prefix_len, redact, redact_len - 1);
+	memcpy(redacted + prefix_len + redact_len - 1, p + at,
+	       suffix_len + 1);
+	return redacted;
 }
 
 /*
@@ -300,6 +321,8 @@ static const char **redact_argv(const char **argv)
 
 	if (!argv[i])
 		return argv;
+	if (!redacted)
+		return NULL;
 
 	for (j = 0; argv[j]; j++)
 		; /* keep counting */
@@ -316,7 +339,14 @@ static const char **redact_argv(const char **argv)
 	ret[i] = redacted;
 	for (++i; argv[i]; i++) {
 		redacted = redact_arg(argv[i]);
-		ret[i] = redacted ? redacted : argv[i];
+		if (!redacted) {
+			for (j = 0; j < i; j++)
+				if (ret[j] != argv[j])
+					free((void *)ret[j]);
+			free(ret);
+			return NULL;
+		}
+		ret[i] = redacted;
 	}
 
 	return ret;
-- 
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