File sudo-1.8.22-CVE-2019-18634.patch of Package sudo.27911

From fa8ffeb17523494f0e8bb49a25e53635f4509078 Mon Sep 17 00:00:00 2001
From: "Todd C. Miller" <Todd.Miller@sudo.ws>
Date: Wed, 29 Jan 2020 20:15:21 -0700
Subject: [PATCH] Fix a buffer overflow when pwfeedback is enabled and input is
 a not a tty. In getln() if the user enters ^U (erase line) and the write(2)
 fails, the remaining buffer size is reset but the current pointer is not.
 While here, fix an incorrect break for erase when write(2) fails. Also
 disable pwfeedback when input is not a tty as it cannot work. CVE-2019-18634
 Credit: Joe Vennix from Apple Information Security.

diff --git a/src/tgetpass.c b/src/tgetpass.c
index 76b0c8b..5eb9f49 100644
--- a/src/tgetpass.c
+++ b/src/tgetpass.c
@@ -60,7 +60,7 @@ static volatile sig_atomic_t signo[NSIG];
 
 static bool tty_present(void);
 static void tgetpass_handler(int);
-static char *getln(int, char *, size_t, int, enum tgetpass_errval *);
+static char *getln(int, char *, size_t, bool, enum tgetpass_errval *);
 static char *sudo_askpass(const char *, const char *);
 
 static int
@@ -123,6 +123,7 @@ tgetpass(const char *prompt, int timeout, int flags,
     static const char *askpass;
     static char buf[SUDO_CONV_REPL_MAX + 1];
     int i, input, output, save_errno, neednl = 0, need_restart;
+    bool feedback = ISSET(flags, TGP_MASK);
     enum tgetpass_errval errval;
     debug_decl(tgetpass, SUDO_DEBUG_CONV)
 
@@ -170,7 +171,7 @@ restart:
      */
     if (!ISSET(flags, TGP_ECHO)) {
 	for (;;) {
-	    if (ISSET(flags, TGP_MASK))
+	    if (feedback)
 		neednl = sudo_term_cbreak(input);
 	    else
 		neednl = sudo_term_noecho(input);
@@ -184,6 +185,9 @@ restart:
 	    }
 	}
     }
+    /* Only use feedback mode when we can disable echo. */
+    if (!neednl)
+	feedback = false;
 
     /*
      * Catch signals that would otherwise cause the user to end
@@ -209,7 +213,7 @@ restart:
 
     if (timeout > 0)
 	alarm(timeout);
-    pass = getln(input, buf, sizeof(buf), ISSET(flags, TGP_MASK), &errval);
+    pass = getln(input, buf, sizeof(buf), feedback, &errval);
     alarm(0);
     save_errno = errno;
 
@@ -345,7 +349,7 @@ sudo_askpass(const char *askpass, const char *prompt)
 extern int sudo_term_eof, sudo_term_erase, sudo_term_kill;
 
 static char *
-getln(int fd, char *buf, size_t bufsiz, int feedback,
+getln(int fd, char *buf, size_t bufsiz, bool feedback,
     enum tgetpass_errval *errval)
 {
     size_t left = bufsiz;
@@ -374,15 +378,15 @@ getln(int fd, char *buf, size_t bufsiz, int feedback,
 		while (cp > buf) {
 		    if (write(fd, "\b \b", 3) == -1)
 			break;
-		    --cp;
+		    cp--;
 		}
+		cp = buf;
 		left = bufsiz;
 		continue;
 	    } else if (c == sudo_term_erase) {
 		if (cp > buf) {
-		    if (write(fd, "\b \b", 3) == -1)
-			break;
-		    --cp;
+		    ignore_result(write(fd, "\b \b", 3));
+		    cp--;
 		    left++;
 		}
 		continue;