Bug 176203 - [patch] devel/gamin: Drop privileges to effective user and group
Summary: [patch] devel/gamin: Drop privileges to effective user and group
Status: Closed FIXED
Alias: None
Product: Ports & Packages
Classification: Unclassified
Component: Individual Port(s) (show other bugs)
Version: Latest
Hardware: Any Any
: Normal Affects Only Me
Assignee: freebsd-gnome (Nobody)
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2013-02-17 03:50 UTC by danny
Modified: 2013-03-22 16:40 UTC (History)
0 users

See Also:


Attachments
file.diff (12.29 KB, patch)
2013-02-17 03:50 UTC, danny
no flags Details | Diff
gamin-drop_privileges.patch.txt (8.30 KB, text/plain; charset=windows-1252)
2013-02-17 04:17 UTC, danny
no flags Details
gamin-drop_privileges.patch.txt (8.27 KB, text/plain; charset=windows-1252)
2013-02-17 04:47 UTC, danny
no flags Details

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Description danny 2013-02-17 03:50:00 UTC
The base release of gamin uses the current real uid to determine the location of the socket and during the security routines.

It also forks off a copy of "gam_server" as the current real uid as well.

This breaks gamin functionality with any application that uses effective an uid/gid for privilege separation, such as samba.

Samba runs as root, but always sets the effective uid/gid to that of the connecting user.  Since gamin is only aware of the real uid, it always creates a root-owned gamin socket that the effective user can't touch (gamin's own security checks refuse it).

For a description of the problem with samba, see:
https://bugzilla.samba.org/show_bug.cgi?id=9558

A similar bug has already been filed against gamin, but has gone unanswered by gamin's maintainer for years:
https://bugzilla.gnome.org/show_bug.cgi?id=345244

This patch adds a "RUN_AS_EUID" definition which will enable the following behavior at compile time:

* use the effective uid to determine the name of user socket to create
* use the effective uid when verifying ownership for security
* runs setuid/setgid to change to the effective uid/gid after forking but before starting a copy of gam_server when run via libgamin
* refuses to escalate privileges to root during setuid/setgid, only dropping privileges (though it would be easy to change that if someone needed it, but I'm erring on the side of caution here since setuid is involved)

I'm not sure which effect this will have on other applications that use gamin, so I leave it up to you to determine the right behavior for the Makefile.  Right now it is provided as a "Drop privileges to effective user" but it may make sense to have it always on by default for security reasons.

It works great on my system so far, though.  This is the first time I have seen samba's file alteration monitoring work on freebsd.

(NOTE: My patch to gam_api.c includes the existing patches, I wasn't sure whether to give you something you can just slap in place that would match svn or provide a patch-of-a-patch)

Fix: Patch attached with submission follows:
Comment 1 Edwin Groothuis freebsd_committer freebsd_triage 2013-02-17 03:50:10 UTC
Responsible Changed
From-To: freebsd-ports-bugs->gnome

Over to maintainer (via the GNATS Auto Assign Tool)
Comment 2 danny 2013-02-17 04:17:55 UTC
Apologies, I forgot to include one of the files in the patch (and 
instead included one of them twice).

Here is an updated patch.
Comment 3 danny 2013-02-17 04:47:01 UTC
Alright, this should hopefully be the last change.

* fixed typo in setgid debug message
* reworked "gamin_drop_privileges" method to accept a uid and gid value 
instead of assuming you always want the effective user, so that it can 
be used in other parts of the code if needed
* changed call to "gamin_drop_privileges" to pass the effective uid/gid 
after fork
Comment 4 danny 2013-03-16 23:02:42 UTC
Has anyone had a chance to look in to this?  Thanks!
Comment 5 dfilter service freebsd_committer freebsd_triage 2013-03-22 16:30:50 UTC
Author: kwm
Date: Fri Mar 22 16:30:36 2013
New Revision: 314945
URL: http://svnweb.freebsd.org/changeset/ports/314945

Log:
  Add patches to gamin to enable support for effective uid/gid, add a option for
  this and turn it on by default.
  
  Current gamin uses the current real uid to determine the location of the
  socket and during the security routines. It also forks off a copy of
  "gam_server" as the current real uid as well.
  
  This breaks gamin functionality with any application that uses effective an
  uid/gid for privilege separation, such as samba. Samba runs as root, but
  always sets the effective uid/gid to that of the connecting user. Since
  gamin is only aware of the real uid, it always creates a root-owned gamin
  socket that the effective user can't touch (gamin's own security checks
  refuse it).
  
  PR:		ports/176203
  Submitted by:	Danny Warren <danny@dannywarren.com>
  Reviewed by:	marcus@

Added:
  head/devel/gamin/files/patch-libgamin_gam_fork.c   (contents, props changed)
  head/devel/gamin/files/patch-libgamin_gam_fork.h   (contents, props changed)
Modified:
  head/devel/gamin/Makefile
  head/devel/gamin/files/patch-libgamin_gam_api.c   (contents, props changed)

Modified: head/devel/gamin/Makefile
==============================================================================
--- head/devel/gamin/Makefile	Fri Mar 22 16:24:53 2013	(r314944)
+++ head/devel/gamin/Makefile	Fri Mar 22 16:30:36 2013	(r314945)
@@ -4,7 +4,7 @@
 
 PORTNAME=	gamin
 PORTVERSION=	0.1.10
-PORTREVISION?=	4
+PORTREVISION?=	5
 CATEGORIES?=	devel
 MASTER_SITES=	http://people.gnome.org/~veillard/gamin/sources/
 
@@ -27,9 +27,11 @@ CONFLICTS=	fam-[0-9]*
 GNU_CONFIGURE=	yes
 
 .if !defined(GAMIN_SLAVE)
-OPTIONS_DEFINE=	GAM_POLLER LIBINOTIFY
+OPTIONS_DEFINE=	GAM_POLLER LIBINOTIFY RUN_AS_EUID
+OPTIONS_DEFAULT=RUN_AS_EUID
 GAM_POLLER_DESC=Use gamin's poller instead of kqueue's
 LIBINOTIFY_DESC=Use libinotify as the FAM backend
+RUN_AS_EUID_DESC=Drop privileges to effective user
 .endif
 
 .include <bsd.port.options.mk>
@@ -48,6 +50,10 @@ CONFIGURE_ARGS+=--disable-inotify
 .endif
 .endif
 
+.if ${PORT_OPTIONS:MRUN_AS_EUID}
+CPPFLAGS+=	-DRUN_AS_EUID=1
+.endif
+
 post-patch:
 	@${REINPLACE_CMD} "s|/etc|${PREFIX}/etc|g" ${WRKSRC}/server/gam_conf.c
 

Modified: head/devel/gamin/files/patch-libgamin_gam_api.c
==============================================================================
--- head/devel/gamin/files/patch-libgamin_gam_api.c	Fri Mar 22 16:24:53 2013	(r314944)
+++ head/devel/gamin/files/patch-libgamin_gam_api.c	Fri Mar 22 16:30:36 2013	(r314945)
@@ -1,5 +1,5 @@
---- libgamin/gam_api.c.orig	Tue Feb  7 17:49:07 2006
-+++ libgamin/gam_api.c	Tue Feb  7 17:49:13 2006
+--- libgamin/gam_api.c.orig	2007-08-27 03:21:03.000000000 -0700
++++ libgamin/gam_api.c	2013-02-16 15:51:11.927100135 -0800
 @@ -14,6 +14,7 @@
  #include <sys/socket.h>
  #include <sys/un.h>
@@ -8,7 +8,43 @@
  #include "fam.h"
  #include "gam_protocol.h"
  #include "gam_data.h"
-@@ -421,10 +422,10 @@
+@@ -117,7 +118,11 @@
+     if (user_name[0] != 0)
+         return (user_name);
+ 
++#ifdef RUN_AS_EUID
++    pw = getpwuid(geteuid());
++#else
+     pw = getpwuid(getuid());
++#endif
+ 
+     if (pw != NULL) {
+ 	strncpy(user_name, pw->pw_name, 99);
+@@ -224,7 +229,11 @@
+ 	free(dir);
+ 	return(0);
+     }
++#ifdef RUN_AS_EUID
++    if (st.st_uid != geteuid()) {
++#else
+     if (st.st_uid != getuid()) {
++#endif
+ 	gam_error(DEBUG_INFO,
+ 		  "Socket directory %s has different owner\n",
+ 		  dir);
+@@ -301,7 +310,11 @@
+     if (ret < 0)
+ 	return(0);
+     
++#ifdef RUN_AS_EUID
++    if (st.st_uid != geteuid()) {
++#else
+     if (st.st_uid != getuid()) {
++#endif
+ 	gam_error(DEBUG_INFO,
+ 		  "Socket %s has different owner\n",
+ 		  path);
+@@ -428,10 +441,10 @@
  {
      char data[2] = { 0, 0 };
      int written;
@@ -22,7 +58,7 @@
      } cmsg;
      struct iovec iov;
      struct msghdr msg;
-@@ -436,16 +437,16 @@
+@@ -443,16 +456,16 @@
      msg.msg_iov = &iov;
      msg.msg_iovlen = 1;
  
@@ -43,7 +79,7 @@
      written = sendmsg(fd, &msg, 0);
  #else
      written = write(fd, &data[0], 1);
-@@ -647,15 +648,16 @@
+@@ -654,15 +667,20 @@
      gid_t c_gid;
  
  #ifdef HAVE_CMSGCRED
@@ -56,14 +92,18 @@
      } cmsg;
  #endif
  
++#ifdef RUN_AS_EUID
++    s_uid = geteuid();
++#else
      s_uid = getuid();
++#endif
  
 -#if defined(LOCAL_CREDS) && defined(HAVE_CMSGCRED)
 +#if defined(LOCAL_CREDS) && defined(HAVE_CMSGCRED) && !defined(__FreeBSD__)
      /* Set the socket to receive credentials on the next message */
      {
          int on = 1;
-@@ -676,8 +678,8 @@
+@@ -683,8 +701,8 @@
  
  #ifdef HAVE_CMSGCRED
      memset(&cmsg, 0, sizeof(cmsg));
@@ -74,7 +114,7 @@
  #endif
  
  retry:
-@@ -694,7 +696,7 @@
+@@ -701,7 +719,7 @@
          goto failed;
      }
  #ifdef HAVE_CMSGCRED
@@ -83,7 +123,7 @@
          GAM_DEBUG(DEBUG_INFO,
                    "Message from recvmsg() was not SCM_CREDS\n");
          goto failed;
-@@ -720,9 +722,10 @@
+@@ -727,9 +745,10 @@
              goto failed;
          }
  #elif defined(HAVE_CMSGCRED)
@@ -97,7 +137,7 @@
  #else /* !SO_PEERCRED && !HAVE_CMSGCRED */
          GAM_DEBUG(DEBUG_INFO,
                    "Socket credentials not supported on this OS\n");
-@@ -1283,14 +1286,17 @@
+@@ -1288,14 +1307,17 @@
  
      // FIXME: drop and reacquire lock while blocked?
      gamin_data_lock(conn);

Added: head/devel/gamin/files/patch-libgamin_gam_fork.c
==============================================================================
--- /dev/null	00:00:00 1970	(empty, because file is newly added)
+++ head/devel/gamin/files/patch-libgamin_gam_fork.c	Fri Mar 22 16:30:36 2013	(r314945)
@@ -0,0 +1,95 @@
+--- libgamin/gam_fork.c.orig	2007-07-04 06:36:48.000000000 -0700
++++ libgamin/gam_fork.c	2013-02-16 20:37:31.298176973 -0800
+@@ -42,6 +42,78 @@
+     return NULL;
+ }
+ 
++#ifdef RUN_AS_EUID
++/**
++ * gamin_drop_privileges
++ *
++ * Attempt to drop privileges to another user and group before forking
++ * a copy of the gam server
++ * 
++ * Return 0 in case of success or -1 in case of detected error.
++ */
++int
++gamin_drop_privileges(int to_uid, int to_gid)
++{
++    GAM_DEBUG(DEBUG_INFO, "Dropping privileges to %d:%d before forking server\n", to_uid, to_gid);
++
++    /* Get the current real user and group */
++    int from_uid = getuid();
++    int from_gid = getgid();
++
++    /* Make sure we were able to get the user and group values */
++    if ( from_uid == -1 || to_uid == -1 || from_gid == -1 || to_gid == -1 ) {
++        gam_error(DEBUG_INFO, "failed to get user or group info, unable to drop privileges\n");
++        return(-1);
++    }
++
++    /* Refuse to run setuid if it would escalate privileges */
++    if ( from_uid != 0 && to_uid == 0 )
++    {
++        gam_error(DEBUG_INFO, "refusing to escalate user privileges from=%d to=%d\n", from_uid, to_uid);
++        return(-1);
++    }
++
++    /* Refuse to run setgid if it would escalate privileges */
++    if ( from_gid != 0 && to_gid == 0 )
++    {
++        gam_error(DEBUG_INFO, "refusing to escalate group privileges from=%d to=%d\n", from_gid, to_gid);
++        return(-1);
++    }
++
++    /* Run setuid to drop privileges to the effective user */
++    if ( from_uid != to_uid ) {
++        GAM_DEBUG(DEBUG_INFO, "Attempting setuid from=%d to=%d\n", from_uid, to_uid);
++
++        /* run setuid and check for errors */
++        if (setuid(to_uid) == -1) {
++            gam_error(DEBUG_INFO, "failed to run setuid from=%d to=%d\n", from_uid, to_uid);
++            return(-1);
++        }
++    }
++    else {
++        GAM_DEBUG(DEBUG_INFO, "Already running as effective user, skipping setuid\n");
++    }
++
++    /* Run setgid to drop privileges to the effective group */
++    if ( from_gid != to_gid ) {
++        GAM_DEBUG(DEBUG_INFO, "Attempting setgid from=%d to=%d\n", from_gid, to_gid);
++
++        /* run setuid and check for errors */
++        if (setgid(to_gid) == -1) {
++            gam_error(DEBUG_INFO, "failed to run setgid from=%d to=%d\n", from_gid, to_gid);
++            return(-1);
++        }
++    }
++    else {
++        GAM_DEBUG(DEBUG_INFO, "Already running as effective group, skipping setgid\n");
++    }
++
++    GAM_DEBUG(DEBUG_INFO, "Succeeded in dropping privileges from %d:%d to %d:%d\n", from_uid, from_gid, to_uid, to_gid);
++
++    return(0);
++}
++#endif
++
+ /**
+  * gamin_fork_server:
+  * @fam_client_id: the client ID string to use
+@@ -71,6 +143,13 @@
+         long open_max;
+ 	long i;
+ 
++#ifdef RUN_AS_EUID
++        /* Drop privileges to the current effective uid/gid and return on failure */
++        if(gamin_drop_privileges( geteuid(), getegid() ) == -1) {
++            return(-1);
++        }
++#endif
++
+         /* don't hold open fd opened from the client of the library */
+ 	open_max = sysconf (_SC_OPEN_MAX);
+ 	for (i = 0; i < open_max; i++)

Added: head/devel/gamin/files/patch-libgamin_gam_fork.h
==============================================================================
--- /dev/null	00:00:00 1970	(empty, because file is newly added)
+++ head/devel/gamin/files/patch-libgamin_gam_fork.h	Fri Mar 22 16:30:36 2013	(r314945)
@@ -0,0 +1,12 @@
+--- libgamin/gam_fork.h.orig	2007-07-04 06:36:48.000000000 -0700
++++ libgamin/gam_fork.h	2013-02-16 20:38:00.328594608 -0800
+@@ -32,6 +32,9 @@
+ #endif
+ 
+ int		gamin_fork_server	(const char *fam_client_id);
++#ifdef RUN_AS_EUID
++int		gamin_drop_privileges	(int to_uid, int to_gid);
++#endif
+ 
+ #ifdef __cplusplus
+ }
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Comment 6 Koop Mast freebsd_committer freebsd_triage 2013-03-22 16:31:07 UTC
State Changed
From-To: open->closed

Committed, thanks!