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 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 #include #include +#include +#include #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 @@ -1321,6 +1321,8 @@ .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 @@ -1208,6 +1208,8 @@ 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