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Description: Allow harmless group-writability
Allow ~/.ssh/config to be group-writable, provided that the group in
question contains only the file's owner. Rejected upstream for IMO
incorrect reasons (e.g. a misunderstanding about the contents of
gr->gr_mem). Given that per-user groups and umask 002 are the default
setup in Debian (for good reasons - this makes operating in setgid
directories with other groups much easier), we need to permit this.
Author: Colin Watson <cjwatson@debian.org>
Bug: https://bugzilla.mindrot.org/show_bug.cgi?id=1060
Bug-Debian: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=314347
Last-Update: 2010-02-27
Index: b/readconf.c
===================================================================
--- a/readconf.c
+++ b/readconf.c
@@ -28,6 +28,8 @@
#include <stdio.h>
#include <string.h>
#include <unistd.h>
+#include <pwd.h>
+#include <grp.h>
#include "xmalloc.h"
#include "ssh.h"
@@ -1000,11 +1002,30 @@
if (checkperm) {
struct stat sb;
+ int bad_modes = 0;
if (fstat(fileno(f), &sb) == -1)
fatal("fstat %s: %s", filename, strerror(errno));
- if (((sb.st_uid != 0 && sb.st_uid != getuid()) ||
- (sb.st_mode & 022) != 0))
+ if (sb.st_uid != 0 && sb.st_uid != getuid())
+ bad_modes = 1;
+ if ((sb.st_mode & 020) != 0) {
+ /* If the file is group-writable, the group in
+ * question must have at most one member, namely the
+ * file's owner.
+ */
+ struct passwd *pw = getpwuid(sb.st_uid);
+ struct group *gr = getgrgid(sb.st_gid);
+ if (!pw || !gr)
+ bad_modes = 1;
+ else if (gr->gr_mem[0]) {
+ if (strcmp(pw->pw_name, gr->gr_mem[0]) ||
+ gr->gr_mem[1])
+ bad_modes = 1;
+ }
+ }
+ if ((sb.st_mode & 002) != 0)
+ bad_modes = 1;
+ if (bad_modes)
fatal("Bad owner or permissions on %s", filename);
}
Index: b/ssh.1
===================================================================
--- a/ssh.1
+++ b/ssh.1
@@ -1324,6 +1324,8 @@
.Xr ssh_config 5 .
Because of the potential for abuse, this file must have strict permissions:
read/write for the user, and not accessible by others.
+It may be group-writable provided that the group in question contains only
+the user.
.Pp
.It ~/.ssh/environment
Contains additional definitions for environment variables; see
Index: b/ssh_config.5
===================================================================
--- a/ssh_config.5
+++ b/ssh_config.5
@@ -1204,6 +1204,8 @@
This file is used by the SSH client.
Because of the potential for abuse, this file must have strict permissions:
read/write for the user, and not accessible by others.
+It may be group-writable provided that the group in question contains only
+the user.
.It Pa /etc/ssh/ssh_config
Systemwide configuration file.
This file provides defaults for those
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