Avoid malloc(3) calls in signal handler

Fetch aborts through SIGINT (^C) print a message with fputs(3), but this
calls malloc() on its own, which is not supported from interrupt handler
context.

Fix it by using write(2) which avoids further memory allocations.
While here, merge abortfile() into the identical aborthttp() with a more
generic "fetch aborted." message for simplicity.

Spotted with vm.malloc_conf=SU and ^C on a port's "make fetch" causing

ftp(49660) in malloc(): recursive call
Abort trap (core dumped)

OK jca (who came up with using write(2) independently)

1 files changed, 4 insertions, 19 deletions

diff --git a/usr.bin/ftp/fetch.c b/usr.bin/ftp/fetch.c
index 5bc9881d25b..e9da609043d 100644
--- a/usr.bin/ftp/fetch.c
+++ b/usr.bin/ftp/fetch.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: fetch.c,v 1.196 2020/07/04 10:18:49 jca Exp $	*/
+/*	$OpenBSD: fetch.c,v 1.197 2020/07/04 11:23:35 kn Exp $	*/
 /*	$NetBSD: fetch.c,v 1.14 1997/08/18 10:20:20 lukem Exp $	*/
 
 /*-
@@ -72,7 +72,6 @@ static int	file_get(const char *, const char *);
 static int	url_get(const char *, const char *, const char *, int);
 static int	save_chunked(FILE *, struct tls *, int , char *, size_t);
 static void	aborthttp(int);
-static void	abortfile(int);
 static char	hextochar(const char *);
 static char	*urldecode(const char *);
 static char	*recode_credentials(const char *_userinfo);
@@ -248,7 +247,7 @@ file_get(const char *path, const char *outfile)
 			(void)signal(SIGINFO, oldinti);
 		goto cleanup_copy;
 	}
-	oldintr = signal(SIGINT, abortfile);
+	oldintr = signal(SIGINT, aborthttp);
 
 	bytes = 0;
 	hashbytes = mark;
@@ -1187,24 +1186,10 @@ save_chunked(FILE *fin, struct tls *tls, int out, char *buf, size_t buflen)
 static void
 aborthttp(int signo)
 {
+	const char errmsg[] = "\nfetch aborted.\n";
 
 	alarmtimer(0);
-	fputs("\nhttp fetch aborted.\n", ttyout);
-	(void)fflush(ttyout);
-	longjmp(httpabort, 1);
-}
-
-/*
- * Abort a http retrieval
- */
-/* ARGSUSED */
-static void
-abortfile(int signo)
-{
-
-	alarmtimer(0);
-	fputs("\nfile fetch aborted.\n", ttyout);
-	(void)fflush(ttyout);
+	write(fileno(ttyout), errmsg, sizeof(errmsg) - 1);
 	longjmp(httpabort, 1);
 }