2 files changed, 37 insertions, 8 deletions
diff --git a/debian/changelog b/debian/changelog
index a27f3b57f..60d985e2f 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -9,6 +9,10 @@ openssh (1:5.5p1-4) UNRELEASED; urgency=low
    group-writable, provided that the group in question contains only the
    file's owner; this extends a patch previously applied to ~/.ssh/config
    (closes: #581919).
+  * Check primary group memberships as well as supplementary group
+    memberships, and only allow group-writability by groups with exactly one
+    member, as zero-member groups are typically used by setgid binaries
+    rather than being user-private groups (closes: #581697).
 -- Colin Watson <cjwatson@debian.org>  Tue, 04 May 2010 13:32:17 +0100
diff --git a/debian/patches/user-group-modes.patch b/debian/patches/user-group-modes.patch
index 8cf862049..164b8ec81 100644
--- a/debian/patches/user-group-modes.patch
+++ b/debian/patches/user-group-modes.patch
@@ -109,7 +109,7 @@ Index: b/misc.c
 #ifdef SSH_TUN_OPENBSD
 #include <net/if.h>
 #endif
-@@ -638,6 +639,30 @@
+@@ -638,6 +639,55 @@
 }
 
 int
@@ -117,22 +117,47 @@ Index: b/misc.c
 +{
 +       if (st->st_uid != 0 && st->st_uid != uid)
 +               return 0;
+       if ((st->st_mode & 002) != 0)
+               return 0;
 +       if ((st->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.
+                * have exactly one member, namely the file's owner.
+                * (Zero-member groups are typically used by setgid
+                * binaries, and are unlikely to be suitable.)
 +                */
-+               struct passwd *pw = getpwuid(st->st_uid);
+               struct passwd *pw;
-+               struct group *gr = getgrgid(st->st_gid);
+               struct group *gr;
-+               if (!pw || !gr)
+               int members = 0;
+
+               gr = getgrgid(st->st_gid);
+               if (!gr)
+                       return 0;
+
+               /* Check primary group memberships. */
+               while ((pw = getpwent()) != NULL) {
+                       if (pw->pw_gid == gr->gr_gid) {
+                               ++members;
+                               if (pw->pw_uid != uid)
+                                       return 0;
+                       }
+               }
+               endpwent();
+
+               pw = getpwuid(st->st_uid);
+               if (!pw)
 +                       return 0;
-+               else if (gr->gr_mem[0]) {
+
+               /* Check supplementary group memberships. */
+               if (gr->gr_mem[0]) {
+                       ++members;
 +                       if (strcmp(pw->pw_name, gr->gr_mem[0]) ||
 +                           gr->gr_mem[1])
 +                               return 0;
 +               }
+
+               if (!members)
+                       return 0;
 +       }
-+       if ((st->st_mode & 002) != 0)
-+               return 0;
 +       return 1;
 +}
 +