when receving a file in sink(), be careful to send at most a single

error response after the file has been opened. Otherwise the source()
and sink() can become desyncronised. Reported by Daniel Goujot,
Georges-Axel Jaloyan, Ryan Lahfa, and David Naccache.

ok deraadt@ markus@

1 files changed, 59 insertions, 37 deletions

diff --git a/usr.bin/ssh/scp.c b/usr.bin/ssh/scp.c
index 4b800268bce..c888a7b8ded 100644
--- a/usr.bin/ssh/scp.c
+++ b/usr.bin/ssh/scp.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: scp.c,v 1.208 2020/04/30 17:07:10 markus Exp $ */
+/* $OpenBSD: scp.c,v 1.209 2020/05/01 06:31:42 djm Exp $ */
 /*
  * scp - secure remote copy.  This is basically patched BSD rcp which
  * uses ssh to do the data transfer (instead of using rcmd).
@@ -354,6 +354,7 @@ BUF *allocbuf(BUF *, int, int);
 void lostconn(int);
 int okname(char *);
 void run_err(const char *,...);
+int note_err(const char *,...);
 void verifydir(char *);
 
 struct passwd *pwd;
@@ -1204,9 +1205,6 @@ sink(int argc, char **argv, const char *src)
 {
 	static BUF buffer;
 	struct stat stb;
-	enum {
-		YES, NO, DISPLAYED
-	} wrerr;
 	BUF *bp;
 	off_t i;
 	size_t j, count;
@@ -1214,7 +1212,7 @@ sink(int argc, char **argv, const char *src)
 	mode_t mode, omode, mask;
 	off_t size, statbytes;
 	unsigned long long ull;
-	int setimes, targisdir, wrerrno = 0;
+	int setimes, targisdir, wrerr;
 	char ch, *cp, *np, *targ, *why, *vect[1], buf[2048], visbuf[2048];
 	char **patterns = NULL;
 	size_t n, npatterns = 0;
@@ -1423,8 +1421,13 @@ bad:			run_err("%s: %s", np, strerror(errno));
 			continue;
 		}
 		cp = bp->buf;
-		wrerr = NO;
+		wrerr = 0;
 
+		/*
+		 * NB. do not use run_err() unless immediately followed by
+		 * exit() below as it may send a spurious reply that might
+		 * desyncronise us from the peer. Use note_err() instead.
+		 */
 		statbytes = 0;
 		if (showprogress)
 			start_progress_meter(curfile, size, &statbytes);
@@ -1449,11 +1452,12 @@ bad:			run_err("%s: %s", np, strerror(errno));
 
 			if (count == bp->cnt) {
 				/* Keep reading so we stay sync'd up. */
-				if (wrerr == NO) {
+				if (!wrerr) {
 					if (atomicio(vwrite, ofd, bp->buf,
 					    count) != count) {
-						wrerr = YES;
-						wrerrno = errno;
+						note_err("%s: %s", np,
+						    strerror(errno));
+						wrerr = 1;
 					}
 				}
 				count = 0;
@@ -1461,56 +1465,42 @@ bad:			run_err("%s: %s", np, strerror(errno));
 			}
 		}
 		unset_nonblock(remin);
-		if (count != 0 && wrerr == NO &&
+		if (count != 0 && !wrerr &&
 		    atomicio(vwrite, ofd, bp->buf, count) != count) {
-			wrerr = YES;
-			wrerrno = errno;
-		}
-		if (wrerr == NO && (!exists || S_ISREG(stb.st_mode)) &&
-		    ftruncate(ofd, size) != 0) {
-			run_err("%s: truncate: %s", np, strerror(errno));
-			wrerr = DISPLAYED;
+			note_err("%s: %s", np, strerror(errno));
+			wrerr = 1;
 		}
+		if (!wrerr && (!exists || S_ISREG(stb.st_mode)) &&
+		    ftruncate(ofd, size) != 0)
+			note_err("%s: truncate: %s", np, strerror(errno));
 		if (pflag) {
 			if (exists || omode != mode)
 				if (fchmod(ofd, omode)) {
-					run_err("%s: set mode: %s",
+					note_err("%s: set mode: %s",
 					    np, strerror(errno));
-					wrerr = DISPLAYED;
 				}
 		} else {
 			if (!exists && omode != mode)
 				if (fchmod(ofd, omode & ~mask)) {
-					run_err("%s: set mode: %s",
+					note_err("%s: set mode: %s",
 					    np, strerror(errno));
-					wrerr = DISPLAYED;
 				}
 		}
-		if (close(ofd) == -1) {
-			wrerr = YES;
-			wrerrno = errno;
-		}
+		if (close(ofd) == -1)
+			note_err(np, "%s: close: %s", np, strerror(errno));
 		(void) response();
 		if (showprogress)
 			stop_progress_meter();
-		if (setimes && wrerr == NO) {
+		if (setimes && !wrerr) {
 			setimes = 0;
 			if (utimes(np, tv) == -1) {
-				run_err("%s: set times: %s",
+				note_err("%s: set times: %s",
 				    np, strerror(errno));
-				wrerr = DISPLAYED;
 			}
 		}
-		switch (wrerr) {
-		case YES:
-			run_err("%s: %s", np, strerror(wrerrno));
-			break;
-		case NO:
+		/* If no error was noted then signal success for this file */
+		if (note_err(NULL) == 0)
 			(void) atomicio(vwrite, remout, "", 1);
-			break;
-		case DISPLAYED:
-			break;
-		}
 	}
 done:
 	for (n = 0; n < npatterns; n++)
@@ -1598,6 +1588,38 @@ run_err(const char *fmt,...)
 	}
 }
 
+/*
+ * Notes a sink error for sending at the end of a file transfer. Returns 0 if
+ * no error has been noted or -1 otherwise. Use note_err(NULL) to flush
+ * any active error at the end of the transfer.
+ */
+int
+note_err(const char *fmt, ...)
+{
+	static char *emsg;
+	va_list ap;
+
+	/* Replay any previously-noted error */
+	if (fmt == NULL) {
+		if (emsg == NULL)
+			return 0;
+		run_err("%s", emsg);
+		free(emsg);
+		emsg = NULL;
+		return -1;
+	}
+
+	errs++;
+	/* Prefer first-noted error */
+	if (emsg != NULL)
+		return -1;
+
+	va_start(ap, fmt);
+	vasnmprintf(&emsg, INT_MAX, NULL, fmt, ap);
+	va_end(ap);
+	return -1;
+}
+
 void
 verifydir(char *cp)
 {