Prevent patch(1) from scribbling all over the place.

Arguably the only sensible use of patch(1) is changing files in the
current working directory and subdirectories.

However, patch(1) has this anti-feature, or dare I say bug, where it
will happily follow "../" upwards and outside of the current working
directory to find files to change. All it takes is a line like
+++ ../../../../home/florian/.ssh/authorized_keys
in the patchfile.

patch(1) operates on untrusted input and it already pledge(2)'ed to
not execute arbitrary programs, but of course it needs to write
files.

A simple unveil(".", "rwc") restricts patch(1) to its current working
directory.

We also need to allow /tmp and potentially the output file and reject
file if given on the command line. But those paths are safe.

input op, deraadt
OK millert, sthen

1 files changed, 34 insertions, 2 deletions

diff --git a/usr.bin/patch/patch.c b/usr.bin/patch/patch.c
index a9740f09ef9..67da2bd23b3 100644
--- a/usr.bin/patch/patch.c
+++ b/usr.bin/patch/patch.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: patch.c,v 1.72 2023/07/12 11:26:13 tb Exp $	*/
+/*	$OpenBSD: patch.c,v 1.73 2023/07/15 10:42:54 florian Exp $	*/
 
 /*
  * patch - a program to apply diffs to original files
@@ -149,7 +149,7 @@ main(int argc, char *argv[])
 	const	char *tmpdir;
 	char	*v;
 
-	if (pledge("stdio rpath wpath cpath tmppath fattr", NULL) == -1) {
+	if (pledge("stdio rpath wpath cpath tmppath fattr unveil", NULL) == -1) {
 		perror("pledge");
 		my_exit(2);
 	}
@@ -204,6 +204,38 @@ main(int argc, char *argv[])
 	Argc = argc;
 	Argv = argv;
 	get_some_switches();
+	if (unveil(tmpdir, "rwc") == -1) {
+		perror("unveil");
+		my_exit(2);
+	}
+	if (outname != NULL)
+		if (unveil(outname, "rwc") == -1) {
+			perror("unveil");
+			my_exit(2);
+		}
+	if (filearg[0] != NULL)
+		if (unveil(filearg[0], "rwc") == -1) {
+			perror("unveil");
+			my_exit(2);
+		}
+	if (filearg[1] != NULL)
+		if (unveil(filearg[1], "r") == -1) {
+			perror("unveil");
+			my_exit(2);
+		}
+	if (unveil(".", "rwc") == -1) {
+		perror("unveil");
+		my_exit(2);
+	}
+	if (*rejname != '\0')
+		if (unveil(rejname, "rwc") == -1) {
+			perror("unveil");
+			my_exit(2);
+		}
+	if (pledge("stdio rpath wpath cpath tmppath fattr", NULL) == -1) {
+		perror("pledge");
+		my_exit(2);
+	}
 
 	if (backup_type == none) {
 		if ((v = getenv("PATCH_VERSION_CONTROL")) == NULL)