upstream: 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@

OpenBSD-Commit-ID: 6c14d233c97349cb811a8f7921ded3ae7d9e0035

1 files changed, 59 insertions, 37 deletions

diff --git a/scp.c b/scp.c
index 812ab5301..439025980 100644
--- a/scp.c
+++ b/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).
@@ -374,6 +374,7 @@ 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;
@@ -1231,9 +1232,6 @@ 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;
@@ -1241,7 +1239,7 @@ 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;
@@ -1450,8 +1448,13 @@ 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);
@@ -1476,11 +1479,12 @@ 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;
@@ -1488,16 +1492,14 @@ 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)
 #ifdef HAVE_FCHMOD
@@ -1505,9 +1507,8 @@ bad:			run_err("%s: %s", np, strerror(errno));
 #else /* HAVE_FCHMOD */
                                 if (chmod(np, omode)) {
 #endif /* HAVE_FCHMOD */
-                                        run_err("%s: set mode: %s",
+                                        note_err("%s: set mode: %s",
                                             np, strerror(errno));
-                                        wrerr = DISPLAYED;
                                 }
                 } else {
                         if (!exists && omode != mode)
@@ -1516,36 +1517,25 @@ bad:			run_err("%s: %s", np, strerror(errno));
 #else /* HAVE_FCHMOD */
                                 if (chmod(np, omode & ~mask)) {
 #endif /* HAVE_FCHMOD */
-                                        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++)
@@ -1633,6 +1623,38 @@ 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)
 {