From 2598ede86241193a9b42d3672a4b3f6098170c3f Mon Sep 17 00:00:00 2001 From: dtucker Date: Tue, 21 Feb 2023 06:48:18 +0000 Subject: [PATCH] fseek to end of known_hosts before writing to it. POSIX and ANSI C require that applications call fseek or similar between read and writing to a RW file. OpenBSD doesn't enforce this, but some (System V derived) platforms need this to prevent it from writing a spurious extra byte (in this case, a newline). ok djm@ deraadt@ --- usr.bin/ssh/hostfile.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-) diff --git a/usr.bin/ssh/hostfile.c b/usr.bin/ssh/hostfile.c index 47b4adea852..dc56ca5058d 100644 --- a/usr.bin/ssh/hostfile.c +++ b/usr.bin/ssh/hostfile.c @@ -1,4 +1,4 @@ -/* $OpenBSD: hostfile.c,v 1.94 2023/02/09 09:54:11 dtucker Exp $ */ +/* $OpenBSD: hostfile.c,v 1.95 2023/02/21 06:48:18 dtucker Exp $ */ /* * Author: Tatu Ylonen * Copyright (c) 1995 Tatu Ylonen , Espoo, Finland @@ -508,7 +508,7 @@ add_host_to_hostfile(const char *filename, const char *host, const struct sshkey *key, int store_hash) { FILE *f; - int success; + int success, addnl = 0; if (key == NULL) return 1; /* XXX ? */ @@ -518,12 +518,13 @@ add_host_to_hostfile(const char *filename, const char *host, return 0; /* Make sure we have a terminating newline. */ if (fseek(f, -1L, SEEK_END) == 0 && fgetc(f) != '\n') - if (fputc('\n', f) != '\n') { - error("Failed to add terminating newline to %s: %s", - filename, strerror(errno)); - fclose(f); - return 0; - } + addnl = 1; + if (fseek(f, 0L, SEEK_END) != 0 || (addnl && fputc('\n', f) != '\n')) { + error("Failed to add terminating newline to %s: %s", + filename, strerror(errno)); + fclose(f); + return 0; + } success = write_host_entry(f, host, NULL, key, store_hash); fclose(f); return success; -- 2.20.1