[src/trunk]: src/external/bsd/nvi/dist/common be more careful about opening r...

[christos <christos%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/f7ba43ed9e27
branches:  trunk
changeset: 827575:f7ba43ed9e27
user:      christos <christos%NetBSD.org@localhost>
date:      Sat Nov 04 03:26:41 2017 +0000

description:
be more careful about opening recovery files... in particular deal with
people trying to get 'vi -r' stuck using named pipes, symlink attacks,
and coercing others opening recovery files they did not create.

diffstat:

 external/bsd/nvi/dist/common/recover.c |  35 ++++++++++++++++++++++++++++++---
 1 files changed, 31 insertions(+), 4 deletions(-)

diffs (74 lines):

diff -r ac72241e5549 -r f7ba43ed9e27 external/bsd/nvi/dist/common/recover.c
--- a/external/bsd/nvi/dist/common/recover.c    Sat Nov 04 02:49:55 2017 +0000
+++ b/external/bsd/nvi/dist/common/recover.c    Sat Nov 04 03:26:41 2017 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: recover.c,v 1.5 2014/01/26 21:43:45 christos Exp $ */
+/*     $NetBSD: recover.c,v 1.6 2017/11/04 03:26:41 christos Exp $ */
 /*-
  * Copyright (c) 1993, 1994
  *     The Regents of the University of California.  All rights reserved.
@@ -16,7 +16,7 @@
 static const char sccsid[] = "Id: recover.c,v 10.31 2001/11/01 15:24:44 skimo Exp  (Berkeley) Date: 2001/11/01 15:24:44 ";
 #endif /* not lint */
 #else
-__RCSID("$NetBSD: recover.c,v 1.5 2014/01/26 21:43:45 christos Exp $");
+__RCSID("$NetBSD: recover.c,v 1.6 2017/11/04 03:26:41 christos Exp $");
 #endif
 
 #include <sys/param.h>
@@ -482,6 +482,22 @@
 }
 
 /*
+ * Since vi creates recovery files only accessible by the user, files
+ * accessible by group or others are probably malicious so avoid them.
+ * This is simpler than checking for getuid() == st.st_uid and we want
+ * to preserve the functionality that root can recover anything which
+ * means that root should know better and be careful.
+ */
+static int
+checkok(int fd)
+{
+       struct stat sb;
+
+       return fstat(fd, &sb) != -1 && S_ISREG(sb.st_mode) &&
+           (sb.st_mode & (S_IRWXG|S_IRWXO)) == 0;
+}
+
+/*
  *     people making love
  *     never exactly the same
  *     just like a snowflake
@@ -525,9 +541,14 @@
                 * if we're using fcntl(2), there's no way to lock a file
                 * descriptor that's not open for writing.
                 */
-               if ((fp = fopen(dp->d_name, "r+")) == NULL)
+               if ((fp = fopen(dp->d_name, "r+efl")) == NULL)
                        continue;
 
+               if (!checkok(fileno(fp))) {
+                       (void)fclose(fp);
+                       continue;
+               }
+
                switch (file_lock(sp, NULL, NULL, fileno(fp), 1)) {
                case LOCK_FAILED:
                        /*
@@ -638,9 +659,15 @@
                 * if we're using fcntl(2), there's no way to lock a file
                 * descriptor that's not open for writing.
                 */
-               if ((fd = open(recpath, O_RDWR, 0)) == -1)
+               if ((fd = open(recpath, O_RDWR|O_NONBLOCK|O_NOFOLLOW|O_CLOEXEC,
+                   0)) == -1)
                        continue;
 
+               if (!checkok(fd)) {
+                       (void)close(fd);
+                       continue;
+               }
+
                switch (file_lock(sp, NULL, NULL, fd, 1)) {
                case LOCK_FAILED:
                        /*