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================================================== ========
==
== Subject: Potential Denial of Service bug in smbd
== CVE ID#: CVE-2007-0452
==
== Versions: Samba 3.0.6 - 3.0.23d (inclusive)
==
== Summary: A logic error in the deferred open code
== can lead to an infinite loop in smbd
==
================================================== ========

===========
Description
===========

Internally Samba's file server daemon, smbd, implements
support for deferred file open calls in an attempt to serve
client requests that would otherwise fail due to a share mode
violation. When renaming a file under certain circumstances
it is possible that the request is never removed from the deferred
open queue. smbd will then become stuck is a loop trying to
service the open request.

This bug may allow an authenticated user to exhaust resources
such as memory and CPU on the server by opening multiple CIFS
sessions, each of which will normally spawn a new smbd process,
and sending each connection into an infinite loop.


==================
Patch Availability
==================

A patch against Samba 3.0.23d has been attached to this
email. This fix has be incorporated into the Samba 3.0.24
release. Patches are also available from at the Samba Security
page (http://www.samba.org/samba/security).


==========
Workaround
==========

The bug is believed to be exploitable only by an authenticated
user. The server's exposure can be alleviated by disabling
any suspect or hostile user accounts.


=======
Credits
=======

This vulnerability was found during internal regression
testing by Samba developers.


================================================== ========
== Our Code, Our Bugs, Our Responsibility.
== The Samba Team
================================================== ========
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diff -urN samba-3.0.23d/source/printing/nt_printing.c samba/source/printing/nt_printing.c
--- samba-3.0.23d/source/printing/nt_printing.c 2006-07-10 11:27:50.000000000 -0500
+++ samba/source/printing/nt_printing.c 2007-01-30 15:00:45.000000000 -0600
@@ -4839,7 +4839,7 @@
pstrcpy( file, s );
driver_unix_convert(file, conn, NULL, &bad_path, &st);
DEBUG(10,("deleting driverfile [%s]\n", s));
- unlink_internals(conn, 0, file, False);
+ unlink_internals(conn, 0, file, False, False);
}
}

@@ -4848,7 +4848,7 @@
pstrcpy( file, s );
driver_unix_convert(file, conn, NULL, &bad_path, &st);
DEBUG(10,("deleting configfile [%s]\n", s));
- unlink_internals(conn, 0, file, False);
+ unlink_internals(conn, 0, file, False, False);
}
}

@@ -4857,7 +4857,7 @@
pstrcpy( file, s );
driver_unix_convert(file, conn, NULL, &bad_path, &st);
DEBUG(10,("deleting datafile [%s]\n", s));
- unlink_internals(conn, 0, file, False);
+ unlink_internals(conn, 0, file, False, False);
}
}

@@ -4866,7 +4866,7 @@
pstrcpy( file, s );
driver_unix_convert(file, conn, NULL, &bad_path, &st);
DEBUG(10,("deleting helpfile [%s]\n", s));
- unlink_internals(conn, 0, file, False);
+ unlink_internals(conn, 0, file, False, False);
}
}

@@ -4882,7 +4882,7 @@
pstrcpy( file, p );
driver_unix_convert(file, conn, NULL, &bad_path, &st);
DEBUG(10,("deleting dependent file [%s]\n", file));
- unlink_internals(conn, 0, file, False);
+ unlink_internals(conn, 0, file, False, False);
}

i++;
diff -urN samba-3.0.23d/source/smbd/nttrans.c samba/source/smbd/nttrans.c
--- samba-3.0.23d/source/smbd/nttrans.c 2006-06-23 08:16:49.000000000 -0500
+++ samba/source/smbd/nttrans.c 2007-01-30 15:00:45.000000000 -0600
@@ -664,7 +664,7 @@
if (lp_acl_check_permissions(SNUM(conn)) && (share_access & FILE_SHARE_DELETE)
&& (access_mask & DELETE_ACCESS)) {
#endif
- status = can_delete(conn, fname, file_attributes, bad_path, True);
+ status = can_delete(conn, fname, file_attributes, bad_path, True, False);
/* We're only going to fail here if it's access denied, as that's the
only error we care about for "can we delete this ?" questions. */
if (!NT_STATUS_IS_OK(status) && (NT_STATUS_EQUAL(status,NT_STATUS_ACCESS_DENIED) ||
@@ -1281,7 +1281,7 @@
/* Setting FILE_SHARE_DELETE is the hint. */
if (lp_acl_check_permissions(SNUM(conn)) && (share_access & FILE_SHARE_DELETE) && (access_mask & DELETE_ACCESS)) {
#endif
- status = can_delete(conn, fname, file_attributes, bad_path, True);
+ status = can_delete(conn, fname, file_attributes, bad_path, True, False);
/* We're only going to fail here if it's access denied, as that's the
only error we care about for "can we delete this ?" questions. */
if (!NT_STATUS_IS_OK(status) && (NT_STATUS_EQUAL(status,NT_STATUS_ACCESS_DENIED) ||
@@ -1888,8 +1888,14 @@

status = rename_internals(conn, fsp->fsp_name,
new_name, 0, replace_if_exists, path_contains_wcard);
- if (!NT_STATUS_IS_OK(status))
+
+ if (!NT_STATUS_IS_OK(status)) {
+ if (open_was_deferred(SVAL(inbuf,smb_mid))) {
+ /* We have re-scheduled this call. */
+ return -1;
+ }
return ERROR_NT(status);
+ }

/*
* Rename was successful.
diff -urN samba-3.0.23d/source/smbd/reply.c samba/source/smbd/reply.c
--- samba-3.0.23d/source/smbd/reply.c 2006-06-23 08:16:49.000000000 -0500
+++ samba/source/smbd/reply.c 2007-01-30 15:00:45.000000000 -0600
@@ -1865,7 +1865,7 @@
Check if a user is allowed to delete a file.
************************************************** ******************/

-NTSTATUS can_delete(connection_struct *conn, char *fname, uint32 dirtype, BOOL bad_path, BOOL check_is_at_open)
+NTSTATUS can_delete(connection_struct *conn, char *fname, uint32 dirtype, BOOL bad_path, BOOL check_is_at_open, BOOL can_defer)
{
SMB_STRUCT_STAT sbuf;
uint32 fattr;
@@ -1938,7 +1938,7 @@
FILE_OPEN,
0,
FILE_ATTRIBUTE_NORMAL,
- 0,
+ can_defer ? 0 : INTERNAL_OPEN_ONLY,
NULL);

if (!fsp) {
@@ -1960,7 +1960,7 @@
code.
************************************************** **************************/

-NTSTATUS unlink_internals(connection_struct *conn, uint32 dirtype, char *name, BOOL has_wild)
+NTSTATUS unlink_internals(connection_struct *conn, uint32 dirtype, char *name, BOOL has_wild, BOOL can_defer)
{
pstring directory;
pstring mask;
@@ -2000,7 +2000,7 @@
if (!has_wild) {
pstrcat(directory,"/");
pstrcat(directory,mask);
- error = can_delete(conn,directory,dirtype,bad_path,False);
+ error = can_delete(conn,directory,dirtype,bad_path,False,c an_defer);
if (!NT_STATUS_IS_OK(error))
return error;

@@ -2058,7 +2058,7 @@
}

slprintf(fname,sizeof(fname)-1, "%s/%s",directory,dname);
- error = can_delete(conn,fname,dirtype,bad_path,False);
+ error = can_delete(conn,fname,dirtype,bad_path,False,False );
if (!NT_STATUS_IS_OK(error)) {
continue;
}
@@ -2104,7 +2104,7 @@

DEBUG(3,("reply_unlink : %s\n",name));

- status = unlink_internals(conn, dirtype, name, path_contains_wcard);
+ status = unlink_internals(conn, dirtype, name, path_contains_wcard, True);
if (!NT_STATUS_IS_OK(status)) {
if (open_was_deferred(SVAL(inbuf,smb_mid))) {
/* We have re-scheduled this call. */
diff -urN samba-3.0.23d/source/smbd/trans2.c samba/source/smbd/trans2.c
--- samba-3.0.23d/source/smbd/trans2.c 2006-11-14 08:42:12.000000000 -0600
+++ samba/source/smbd/trans2.c 2007-01-30 15:00:35.000000000 -0600
@@ -4446,9 +4446,15 @@
fname, newname ));
status = rename_internals(conn, fname, base_name, 0, overwrite, False);
}
+
if (!NT_STATUS_IS_OK(status)) {
+ if (open_was_deferred(SVAL(inbuf,smb_mid))) {
+ /* We have re-scheduled this call. */
+ return -1;
+ }
return ERROR_NT(status);
}
+
process_pending_change_notify_queue((time_t)0);
SSVAL(params,0,0);
send_trans2_replies(outbuf, bufsize, params, 2, *ppdata, 0);












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