[PATCH] support >16 supplementary groups on Darwin

[James Peach]

Hi all,

The attached patch add support for groups lists of more that 16 on  
Darwin/Mac OS X. This requires that we perform a very specific dance  
when switching our UNIX credential.

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diff --git a/source/configure.in b/source/configure.in
index be92a91..d69a40e 100644
--- a/source/configure.in
+++ b/source/configure.in
@@ -3100,6 +3100,21 @@ if test x"$samba_cv_USE_SETUIDX" = x"yes"; then
 fi
 fi
 
+AC_CACHE_CHECK([for the Darwin initgroups system call],
+	samba_cv_DARWIN_INITGROUPS,
+	AC_TRY_LINK([
+#include <sys/syscall.h>
+#include <unistd.h>
+	],
+	[ syscall(SYS_initgroups, 16, NULL, NULL, 0); ],
+	samba_cv_DARWIN_INITGROUPS=yes,
+	samba_cv_DARWIN_INITGROUPS=no)
+)
+
+if test x"$samba_cv_DARWIN_INITGROUPS" = x"yes" ; then
+    AC_DEFINE(HAVE_DARWIN_INITGROUPS, 1,
+	[Whether to use the Darwin-specific initgroups system call])
+fi
 
 AC_CACHE_CHECK([for working mmap],samba_cv_HAVE_MMAP,[
 AC_TRY_RUN([#include "${srcdir-.}/tests/shared_mmap.c"],
diff --git a/source/smbd/sec_ctx.c b/source/smbd/sec_ctx.c
index fd79fbb..6a2d389 100644
--- a/source/smbd/sec_ctx.c
+++ b/source/smbd/sec_ctx.c
@@ -231,6 +231,10 @@ BOOL push_sec_ctx(void)
  Change UNIX security context. Calls panic if not successful so no return value.
 ****************************************************************************/
 
+#ifndef HAVE_DARWIN_INITGROUPS
+
+/* Normal credential switch path. */
+
 static void set_unix_security_ctx(uid_t uid, gid_t gid, int ngroups, gid_t *groups)
 {
 	/* Start context switch */
@@ -242,6 +246,51 @@ static void set_unix_security_ctx(uid_t uid, gid_t gid, int ngroups, gid_t *grou
 	/* end context switch */
 }
 
+#else /* HAVE_DARWIN_INITGROUPS */
+
+/* The Darwin groups implementation is a little unusual. The list of
+* groups in the kernel credential is not exhaustive, but more like
+* a cache. The full group list is held in userspace and checked
+* dynamically.
+*
+* This is an optional mechanism, and setgroups(2) opts out
+* of it. That is, if you call setgroups, then the list of groups you
+* set are the only groups that are ever checked. This is not what we
+* want. We want to opt in to the dynamic resolution mechanism, so we
+* need to specify the uid of the user whose group list (cache) we are
+* setting.
+*
+* The Darwin rules are:
+*  1. Thou shalt setegid, initgroups and seteuid IN THAT ORDER
+*  2. Thou shalt not pass more that NGROUPS_MAX to initgroups
+*  3. Thou shalt leave the first entry in the groups list well alone
+*/
+
+#include <sys/syscall.h>
+
+static void set_unix_security_ctx(uid_t uid, gid_t gid, int ngroups, gid_t *groups)
+{
+	int max = groups_max();
+
+	/* Start context switch */
+	gain_root();
+
+	become_gid(gid);
+
+
+	if (syscall(SYS_initgroups, (ngroups > max) ? max : ngroups,
+			groups, uid) == 1) {
+		DEBUG(0, ("WARNING: failed to set group list "
+			"(%d groups) for UID %ld: %s\n",
+			ngroups, uid, strerror(errno)));
+	}
+
+	become_uid(uid);
+	/* end context switch */
+}
+
+#endif /* HAVE_DARWIN_INITGROUPS */
+
 /****************************************************************************
  Set the current security context to a given user.
 ****************************************************************************/
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--
James Peach | jpeach at samba.org