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Revision 712f3147aee0fbbbbed2da20b21b272c5505125e authored by Linus Torvalds on 13 May 2011, 23:16:41 UTC, committed by Linus Torvalds on 14 May 2011, 17:23:44 UTC 
fbmem: fix remove_conflicting_framebuffers races
 
When a register_framebuffer() call results in us removing old
conflicting framebuffers, the new registration_lock doesn't protect that
situation.  And we can't just add the same locking to the function,
because these functions call each other: register_framebuffer() calls
remove_conflicting_framebuffers, which in turn calls
unregister_framebuffer for any conflicting entry.

In order to fix it, this just creates wrapper functions around all three
functions and makes the versions that actually do the work be called
"do_xxx()", leaving just the wrapper that gets the lock and calls the
worker function.

So the rule becomes simply that "do_xxxx()" has to be called with the
lock held, and now do_register_framebuffer() can just call
do_remove_conflicting_framebuffers(), and that in turn can call
_do_unregister_framebuffer(), and there is no deadlock, and we can hold
the registration lock over the whole sequence, fixing the races.

It also makes error cases simpler, and fixes one situation where we
would return from unregister_framebuffer() without releasing the lock,
pointed out by Bruno Prémont.

Tested-by: Bruno Prémont <bonbons@linux-vserver.org>
Tested-by: Anca Emanuel <anca.emanuel@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Raw File
diag.c 
/*
 *  net/dccp/diag.c
 *
 *  An implementation of the DCCP protocol
 *  Arnaldo Carvalho de Melo <acme@mandriva.com>
 *
 *	This program is free software; you can redistribute it and/or modify it
 *	under the terms of the GNU General Public License version 2 as
 *	published by the Free Software Foundation.
 */


#include <linux/module.h>
#include <linux/inet_diag.h>

#include "ccid.h"
#include "dccp.h"

static void dccp_get_info(struct sock *sk, struct tcp_info *info)
{
	struct dccp_sock *dp = dccp_sk(sk);
	const struct inet_connection_sock *icsk = inet_csk(sk);

	memset(info, 0, sizeof(*info));

	info->tcpi_state	= sk->sk_state;
	info->tcpi_retransmits	= icsk->icsk_retransmits;
	info->tcpi_probes	= icsk->icsk_probes_out;
	info->tcpi_backoff	= icsk->icsk_backoff;
	info->tcpi_pmtu		= icsk->icsk_pmtu_cookie;

	if (dp->dccps_hc_rx_ackvec != NULL)
		info->tcpi_options |= TCPI_OPT_SACK;

	if (dp->dccps_hc_rx_ccid != NULL)
		ccid_hc_rx_get_info(dp->dccps_hc_rx_ccid, sk, info);

	if (dp->dccps_hc_tx_ccid != NULL)
		ccid_hc_tx_get_info(dp->dccps_hc_tx_ccid, sk, info);
}

static void dccp_diag_get_info(struct sock *sk, struct inet_diag_msg *r,
			       void *_info)
{
	r->idiag_rqueue = r->idiag_wqueue = 0;

	if (_info != NULL)
		dccp_get_info(sk, _info);
}

static const struct inet_diag_handler dccp_diag_handler = {
	.idiag_hashinfo	 = &dccp_hashinfo,
	.idiag_get_info	 = dccp_diag_get_info,
	.idiag_type	 = DCCPDIAG_GETSOCK,
	.idiag_info_size = sizeof(struct tcp_info),
};

static int __init dccp_diag_init(void)
{
	return inet_diag_register(&dccp_diag_handler);
}

static void __exit dccp_diag_fini(void)
{
	inet_diag_unregister(&dccp_diag_handler);
}

module_init(dccp_diag_init);
module_exit(dccp_diag_fini);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Arnaldo Carvalho de Melo <acme@mandriva.com>");
MODULE_DESCRIPTION("DCCP inet_diag handler");
MODULE_ALIAS_NET_PF_PROTO_TYPE(PF_NETLINK, NETLINK_INET_DIAG, DCCPDIAG_GETSOCK);
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