scp: validate filenames provided by server against wildcard in client

OpenSSH-portable commits:

check in scp client that filenames sent during remote->local directory
copies satisfy the wildcard specified by the user.

This checking provides some protection against a malicious server
sending unexpected filenames, but it comes at a risk of rejecting wanted
files due to differences between client and server wildcard expansion rules.

For this reason, this also adds a new -T flag to disable the check.

reported by Harry Sintonen
fix approach suggested by markus@;
has been in snaps for ~1wk courtesy deraadt@

OpenBSD-Commit-ID: 00f44b50d2be8e321973f3c6d014260f8f7a8eda

Minor patch conflict (getopt) resolved.

Obtained from: OpenSSH-portable 391ffc4b9d31fa1f4ad566499fef9176ff8a07dc

scp: add -T to usage();

OpenBSD-Commit-ID: a7ae14d9436c64e1bd05022329187ea3a0ce1899

Obtained from: OpenSSH-portable 2c21b75a7be6ebdcbceaebb43157c48dbb36f3d8

PR:		234965
Approved by:	des
MFC after:	3 days
Obtained from:	OpenSSH-portable 391ffc4b9d, 2c21b75a7b
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D19076

crypto/openssh/scp.1

@@ -18,7 +18,7 @@
 .Nd secure copy (remote file copy program)
 .Sh SYNOPSIS
 .Nm scp
-.Op Fl 346BCpqrv
+.Op Fl 346BCpqrTv
 .Op Fl c Ar cipher
 .Op Fl F Ar ssh_config
 .Op Fl i Ar identity_file
@@ -207,6 +207,16 @@ to use for the encrypted connection.
 The program must understand
 .Xr ssh 1
 options.
+.It Fl T
+Disable strict filename checking.
+By default when copying files from a remote host to a local directory
+.Nm
+checks that the received filenames match those requested on the command-line
+to prevent the remote end from sending unexpected or unwanted files.
+Because of differences in how various operating systems and shells interpret
+filename wildcards, these checks may cause wanted files to be rejected.
+This option disables these checks at the expense of fully trusting that
+the server will not send unexpected filenames.
 .It Fl v
 Verbose mode.
 Causes

crypto/openssh/scp.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: scp.c,v 1.197 2018/06/01 04:31:48 dtucker Exp $ */
+/* $OpenBSD: scp.c,v 1.203 2019/01/27 07:14:11 jmc Exp $ */
 /*
  * scp - secure remote copy.  This is basically patched BSD rcp which
  * uses ssh to do the data transfer (instead of using rcmd).
@@ -94,6 +94,7 @@
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <fnmatch.h>
 #include <limits.h>
 #include <locale.h>
 #include <pwd.h>
@@ -375,14 +376,14 @@ void verifydir(char *);
 struct passwd *pwd;
 uid_t userid;
 int errs, remin, remout;
-int pflag, iamremote, iamrecursive, targetshouldbedirectory;
+int Tflag, pflag, iamremote, iamrecursive, targetshouldbedirectory;
 
 #define	CMDNEEDS	64
 char cmd[CMDNEEDS];		/* must hold "rcp -r -p -d\0" */
 
 int response(void);
 void rsource(char *, struct stat *);
-void sink(int, char *[]);
+void sink(int, char *[], const char *);
 void source(int, char *[]);
 void tolocal(int, char *[]);
 void toremote(int, char *[]);
@@ -421,8 +422,9 @@ main(int argc, char **argv)
 	addargs(&args, "-oRemoteCommand=none");
 	addargs(&args, "-oRequestTTY=no");
 
-	fflag = tflag = 0;
+	fflag = Tflag = tflag = 0;
-	while ((ch = getopt(argc, argv, "dfl:prtvBCc:i:P:q12346S:o:F:")) != -1)
+	while ((ch = getopt(argc, argv,
+	    "dfl:prtTvBCc:i:P:q12346S:o:F:")) != -1) {
 		switch (ch) {
 		/* User-visible flags. */
 		case '1':
@@ -501,9 +503,13 @@ main(int argc, char **argv)
 			setmode(0, O_BINARY);
 #endif
 			break;
+		case 'T':
+			Tflag = 1;
+			break;
 		default:
 			usage();
 		}
+	}
 	argc -= optind;
 	argv += optind;
 
@@ -534,7 +540,7 @@ main(int argc, char **argv)
 	}
 	if (tflag) {
 		/* Receive data. */
-		sink(argc, argv);
+		sink(argc, argv, NULL);
 		exit(errs != 0);
 	}
 	if (argc < 2)
@@ -791,7 +797,7 @@ tolocal(int argc, char **argv)
 			continue;
 		}
 		free(bp);
-		sink(1, argv + argc - 1);
+		sink(1, argv + argc - 1, src);
 		(void) close(remin);
 		remin = remout = -1;
 	}
@@ -967,7 +973,7 @@ rsource(char *name, struct stat *statp)
 	 (sizeof(type) != 4 && sizeof(type) != 8))
 
 void
-sink(int argc, char **argv)
+sink(int argc, char **argv, const char *src)
 {
 	static BUF buffer;
 	struct stat stb;
@@ -983,6 +989,7 @@ sink(int argc, char **argv)
 	unsigned long long ull;
 	int setimes, targisdir, wrerrno = 0;
 	char ch, *cp, *np, *targ, *why, *vect[1], buf[2048], visbuf[2048];
+	char *src_copy = NULL, *restrict_pattern = NULL;
 	struct timeval tv[2];
 
 #define	atime	tv[0]
@@ -1007,6 +1014,17 @@ sink(int argc, char **argv)
 	(void) atomicio(vwrite, remout, "", 1);
 	if (stat(targ, &stb) == 0 && S_ISDIR(stb.st_mode))
 		targisdir = 1;
+	if (src != NULL && !iamrecursive && !Tflag) {
+		/*
+		 * Prepare to try to restrict incoming filenames to match
+		 * the requested destination file glob.
+		 */
+		if ((src_copy = strdup(src)) == NULL)
+			fatal("strdup failed");
+		if ((restrict_pattern = strrchr(src_copy, '/')) != NULL) {
+			*restrict_pattern++ = '\0';
+		}
+	}
 	for (first = 1;; first = 0) {
 		cp = buf;
 		if (atomicio(read, remin, cp, 1) != 1)
@@ -1111,6 +1129,9 @@ sink(int argc, char **argv)
 			run_err("error: unexpected filename: %s", cp);
 			exit(1);
 		}
+		if (restrict_pattern != NULL &&
+		    fnmatch(restrict_pattern, cp, 0) != 0)
+			SCREWUP("filename does not match request");
 		if (targisdir) {
 			static char *namebuf;
 			static size_t cursize;
@@ -1148,7 +1169,7 @@ sink(int argc, char **argv)
 					goto bad;
 			}
 			vect[0] = xstrdup(np);
-			sink(1, vect);
+			sink(1, vect, src);
 			if (setimes) {
 				setimes = 0;
 				if (utimes(vect[0], tv) < 0)
@@ -1316,7 +1337,7 @@ void
 usage(void)
 {
 	(void) fprintf(stderr,
-	    "usage: scp [-346BCpqrv] [-c cipher] [-F ssh_config] [-i identity_file]\n"
+	    "usage: scp [-346BCpqrTv] [-c cipher] [-F ssh_config] [-i identity_file]\n"
 	    "           [-l limit] [-o ssh_option] [-P port] [-S program] source ... target\n");
 	exit(1);
 }