tftpd: Verify world-writability for WRQ when using relative paths

tftpd(8) says that files may only be written if they already exist and are
publicly writable.  tftpd.c verifies that a file is publicly writable if it
uses an absolute pathname.  However, if the pathname is relative, that check
is skipped.  Fix it.

Note that this is not a security vulnerability, because the transfer
ultimately doesn't work unless the file already exists and is owned by user
nobody.  Also, this bug does not affect the default configuration, because
the default uses the "-s" option which makes all pathnames absolute.

PR:		226004
MFC after:	3 weeks

2 files changed, 17 insertions, 6 deletions

diff --git a/libexec/tftpd/tests/functional.c b/libexec/tftpd/tests/functional.c
index d7f5ac77f81b4..4d0992e29e0e6 100644
--- a/libexec/tftpd/tests/functional.c
+++ b/libexec/tftpd/tests/functional.c
@@ -350,6 +350,10 @@ setup(struct sockaddr_storage *to, uint16_t idx)
 		ATF_REQUIRE((client_s = socket(protocol, SOCK_DGRAM, 0)) > 0);
 		break;
 	}
+
+	/* Clear the client's umask.  Test cases will specify exact modes */
+	umask(0000);
+
 	return (client_s);
 }
 
@@ -714,7 +718,7 @@ TFTPD_TC_DEFINE(wrq_dropped_ack,)
 	for (i = 0; i < nitems(contents); i++)
 		contents[i] = i;
 
-	fd = open("medium.txt", O_RDWR | O_CREAT, 0644);
+	fd = open("medium.txt", O_RDWR | O_CREAT, 0666);
 	ATF_REQUIRE(fd >= 0);
 	close(fd);
 
@@ -747,7 +751,7 @@ TFTPD_TC_DEFINE(wrq_dropped_data,)
 	size_t contents_len;
 	char buffer[1024];
 
-	fd = open("small.txt", O_RDWR | O_CREAT, 0644);
+	fd = open("small.txt", O_RDWR | O_CREAT, 0666);
 	ATF_REQUIRE(fd >= 0);
 	close(fd);
 	contents_len = strlen(contents) + 1;
@@ -782,7 +786,7 @@ TFTPD_TC_DEFINE(wrq_duped_data,)
 	for (i = 0; i < nitems(contents); i++)
 		contents[i] = i;
 
-	fd = open("medium.txt", O_RDWR | O_CREAT, 0644);
+	fd = open("medium.txt", O_RDWR | O_CREAT, 0666);
 	ATF_REQUIRE(fd >= 0);
 	close(fd);
 
@@ -831,7 +835,8 @@ TFTPD_TC_DEFINE(wrq_eaccess_world_readable,)
 	close(fd);
 
 	SEND_WRQ("empty.txt", "octet");
-	atf_tc_expect_fail("PR 226004 with relative pathnames, tftpd doesn't validate world writability");
+	atf_tc_expect_fail("PR 225996 tftpd doesn't abort on a WRQ access "
+	    "violation");
 	RECV_ERROR(2, "Access violation");
 }
 
diff --git a/libexec/tftpd/tftpd.c b/libexec/tftpd/tftpd.c
index a167395d58321..94f2f52be808b 100644
--- a/libexec/tftpd/tftpd.c
+++ b/libexec/tftpd/tftpd.c
@@ -743,8 +743,12 @@ validate_access(int peer, char **filep, int mode)
 				dirp->name, filename);
 			if (stat(pathname, &stbuf) == 0 &&
 			    (stbuf.st_mode & S_IFMT) == S_IFREG) {
-				if ((stbuf.st_mode & S_IROTH) != 0) {
-					break;
+				if (mode == RRQ) {
+					if ((stbuf.st_mode & S_IROTH) != 0)
+						break;
+				} else {
+					if ((stbuf.st_mode & S_IWOTH) != 0)
+						break;
 				}
 				err = EACCESS;
 			}
@@ -753,6 +757,8 @@ validate_access(int peer, char **filep, int mode)
 			*filep = filename = pathname;
 		else if (mode == RRQ)
 			return (err);
+		else if (err != ENOTFOUND || !create_new)
+			return (err);
 	}
 
 	/*