1 files changed, 145 insertions, 0 deletions
diff --git a/lib/agetpass.c b/lib/agetpass.c
new file mode 100644
index 0000000..5d9f928
--- /dev/null
+++ b/lib/agetpass.c
@@ -0,0 +1,145 @@
+/*
+ * SPDX-FileCopyrightText:  2022, Alejandro Colomar <alx@kernel.org>
+ *
+ * SPDX-License-Identifier:  BSD-3-Clause
+ */
+
+
+#include <config.h>
+
+#include "agetpass.h"
+
+#include <limits.h>
+#include <readpassphrase.h>
+#include <stdlib.h>
+#include <string.h>
+
+#ident "$Id$"
+
+#include "alloc.h"
+
+#if WITH_LIBBSD == 0
+#include "freezero.h"
+#endif /* WITH_LIBBSD */
+
+
+/*
+ * SYNOPSIS
+ *	[[gnu::malloc(erase_pass)]]
+ *	char *agetpass(const char *prompt);
+ *	char *agetpass_stdin();
+ *
+ *	void erase_pass(char *pass);
+ *
+ * ARGUMENTS
+ *   agetpass()
+ *	prompt	String to be printed before reading a password.
+ *
+ *   erase_pass()
+ *	pass	password previously returned by agetpass().
+ *
+ * DESCRIPTION
+ *   agetpass()
+ *	This function is very similar to getpass(3).  It has several
+ *	advantages compared to getpass(3):
+ *
+ *	- Instead of using a static buffer, agetpass() allocates memory
+ *	  through malloc(3).  This makes the function thread-safe, and
+ *	  also reduces the visibility of the buffer.
+ *
+ *	- agetpass() doesn't reallocate internally.  Some
+ *	  implementations of getpass(3), such as glibc, do that, as a
+ *	  consequence of calling getline(3).  That's a bug in glibc,
+ *	  which allows leaking prefixes of passwords in freed memory.
+ *
+ *	- agetpass() doesn't overrun the output buffer.  If the input
+ *	  password is too long, it simply fails.  Some implementations
+ *	  of getpass(3), share the same bug that gets(3) has.
+ *
+ *	As soon as possible, the password obtained from agetpass() be
+ *	erased by calling erase_pass(), to avoid possibly leaking the
+ *	password.
+ *
+ *   agetpass_stdin()
+ *	This function is the same as previous one (agetpass). Just the
+ *	password is read from stdin and terminal is not required.
+ *
+ *   erase_pass()
+ *	This function first clears the password, by calling
+ *	explicit_bzero(3) (or an equivalent call), and then frees the
+ *	allocated memory by calling free(3).
+ *
+ *	NULL is a valid input pointer, and in such a case, this call is
+ *	a no-op.
+ *
+ * RETURN VALUE
+ *	agetpass() returns a newly allocated buffer containing the
+ *	password on success.  On error, errno is set to indicate the
+ *	error, and NULL is returned.
+ *
+ * ERRORS
+ *   agetpass()
+ *	This function may fail for any errors that malloc(3) or
+ *	readpassphrase(3) may fail, and in addition it may fail for the
+ *	following errors:
+ *
+ *	ENOBUFS
+ *		The input password was longer than PASS_MAX.
+ *
+ * CAVEATS
+ *	If a password is passed twice to erase_pass(), the behavior is
+ *	undefined.
+ */
+
+
+static char *
+agetpass_internal(const char *prompt, int flags)
+{
+	char    *pass;
+	size_t  len;
+
+	/*
+	 * Since we want to support passwords upto PASS_MAX, we need
+	 * PASS_MAX bytes for the password itself, and one more byte for
+	 * the terminating '\0'.  We also want to detect truncation, and
+	 * readpassphrase(3) doesn't detect it, so we need some trick.
+	 * Let's add one more byte, and if the password uses it, it
+	 * means the introduced password was longer than PASS_MAX.
+	 */
+	pass = MALLOC(PASS_MAX + 2, char);
+	if (pass == NULL)
+		return NULL;
+
+	if (readpassphrase(prompt, pass, PASS_MAX + 2, flags) == NULL)
+		goto fail;
+
+	len = strlen(pass);
+	if (len == PASS_MAX + 1) {
+		errno = ENOBUFS;
+		goto fail;
+	}
+
+	return pass;
+
+fail:
+	freezero(pass, PASS_MAX + 2);
+	return NULL;
+}
+
+char *
+agetpass(const char *prompt)
+{
+	return agetpass_internal(prompt, RPP_REQUIRE_TTY);
+}
+
+char *
+agetpass_stdin()
+{
+	return agetpass_internal(NULL, RPP_STDIN);
+}
+
+void
+erase_pass(char *pass)
+{
+	freezero(pass, PASS_MAX + 2);
+}