4c0c03ca54
Fix the security problem in the CIFS filesystem DNS lookup code in which a
malicious redirect could be installed by a random user by simply adding a
result record into one of their keyrings with add_key() and then invoking a
CIFS CFS lookup [CVE-2010-2524].
This is done by creating an internal keyring specifically for the caching of
DNS lookups. To enforce the use of this keyring, the module init routine
creates a set of override credentials with the keyring installed as the thread
keyring and instructs request_key() to only install lookup result keys in that
keyring.
The override is then applied around the call to request_key().
This has some additional benefits when a kernel service uses this module to
request a key:
(1) The result keys are owned by root, not the user that caused the lookup.
(2) The result keys don't pop up in the user's keyrings.
(3) The result keys don't come out of the quota of the user that caused the
lookup.
The keyring can be viewed as root by doing cat /proc/keys:
2a0ca6c3 I----- 1 perm 1f030000 0 0 keyring .dns_resolver: 1/4
It can then be listed with 'keyctl list' by root.
# keyctl list 0x2a0ca6c3
1 key in keyring:
726766307: --alswrv 0 0 dns_resolver: foo.bar.com
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-and-Tested-by: Jeff Layton <jlayton@redhat.com>
Acked-by: Steve French <smfrench@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
33 lines
1.3 KiB
C
33 lines
1.3 KiB
C
/*
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* fs/cifs/dns_resolve.h -- DNS Resolver upcall management for CIFS DFS
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* Handles host name to IP address resolution
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*
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* Copyright (c) International Business Machines Corp., 2008
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* Author(s): Steve French (sfrench@us.ibm.com)
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*
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* This library is free software; you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as published
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* by the Free Software Foundation; either version 2.1 of the License, or
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* (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
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* the GNU Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public License
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* along with this library; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#ifndef _DNS_RESOLVE_H
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#define _DNS_RESOLVE_H
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#ifdef __KERNEL__
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extern int __init cifs_init_dns_resolver(void);
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extern void __exit cifs_exit_dns_resolver(void);
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extern int dns_resolve_server_name_to_ip(const char *unc, char **ip_addr);
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#endif /* KERNEL */
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#endif /* _DNS_RESOLVE_H */
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