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Commit 78c2e502 authored by Pavel Emelyanov's avatar Pavel Emelyanov Committed by David S. Miller
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[IPV6]: Fix race in ipv6_flowlabel_opt() when inserting two labels 



In the IPV6_FL_A_GET case the hash is checked for flowlabels
with the given label. If it is not found, the lock, protecting 
the hash, is dropped to be re-get for writing. After this a
newly allocated entry is inserted, but no checks are performed
to catch a classical SMP race, when the conflicting label may 
be inserted on another cpu.

Use the (currently unused) return value from fl_intern() to
return the conflicting entry (if found) and re-check, whether
we can reuse it (IPV6_FL_F_EXCL) or return -EEXISTS.

Also add the comment, about why not re-lookup the current
sock for conflicting flowlabel entry.

Signed-off-by: default avatarPavel Emelyanov <xemul@openvz.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent bd0bf577

net/ipv6/ip6_flowlabel.c

+25 −9
Original line number Diff line number Diff line
@@ -154,8 +154,10 @@ static void ip6_fl_gc(unsigned long dummy) 
	write_unlock(&ip6_fl_lock);

}



static int fl_intern(struct ip6_flowlabel *fl, __be32 label)

static struct ip6_flowlabel *fl_intern(struct ip6_flowlabel *fl, __be32 label)

{

	struct ip6_flowlabel *lfl;



	fl->label = label & IPV6_FLOWLABEL_MASK;



	write_lock_bh(&ip6_fl_lock);
@@ -163,12 +165,26 @@ static int fl_intern(struct ip6_flowlabel *fl, __be32 label) 
		for (;;) {

			fl->label = htonl(net_random())&IPV6_FLOWLABEL_MASK;

			if (fl->label) {

				struct ip6_flowlabel *lfl;

				lfl = __fl_lookup(fl->label);

				if (lfl == NULL)

					break;

			}

		}

	} else {

		/*

		 * we dropper the ip6_fl_lock, so this entry could reappear

		 * and we need to recheck with it.

		 *

		 * OTOH no need to search the active socket first, like it is

		 * done in ipv6_flowlabel_opt - sock is locked, so new entry

		 * with the same label can only appear on another sock

		 */

		lfl = __fl_lookup(fl->label);

		if (lfl != NULL) {

			atomic_inc(&lfl->users);

			write_unlock_bh(&ip6_fl_lock);

			return lfl;

		}

	}



	fl->lastuse = jiffies;
@@ -176,7 +192,7 @@ static int fl_intern(struct ip6_flowlabel *fl, __be32 label) 
	fl_ht[FL_HASH(fl->label)] = fl;

	atomic_inc(&fl_size);

	write_unlock_bh(&ip6_fl_lock);

	return 0;

	return NULL;

}
@@ -429,7 +445,8 @@ int ipv6_flowlabel_opt(struct sock *sk, char __user *optval, int optlen) 
	struct in6_flowlabel_req freq;

	struct ipv6_fl_socklist *sfl1=NULL;

	struct ipv6_fl_socklist *sfl, **sflp;

	struct ip6_flowlabel *fl;

	struct ip6_flowlabel *fl, *fl1 = NULL;





	if (optlen < sizeof(freq))

		return -EINVAL;
@@ -485,8 +502,6 @@ int ipv6_flowlabel_opt(struct sock *sk, char __user *optval, int optlen) 
		sfl1 = kmalloc(sizeof(*sfl1), GFP_KERNEL);



		if (freq.flr_label) {

			struct ip6_flowlabel *fl1 = NULL;



			err = -EEXIST;

			read_lock_bh(&ip6_sk_fl_lock);

			for (sfl = np->ipv6_fl_list; sfl; sfl = sfl->next) {
@@ -505,6 +520,7 @@ int ipv6_flowlabel_opt(struct sock *sk, char __user *optval, int optlen) 
			if (fl1 == NULL)

				fl1 = fl_lookup(freq.flr_label);

			if (fl1) {

recheck:

				err = -EEXIST;

				if (freq.flr_flags&IPV6_FL_F_EXCL)

					goto release;
@@ -543,9 +559,9 @@ int ipv6_flowlabel_opt(struct sock *sk, char __user *optval, int optlen) 
		if (sfl1 == NULL || (err = mem_check(sk)) != 0)

			goto done;



		err = fl_intern(fl, freq.flr_label);

		if (err)

			goto done;

		fl1 = fl_intern(fl, freq.flr_label);

		if (fl1 != NULL)

			goto recheck;



		if (!freq.flr_label) {

			if (copy_to_user(&((struct in6_flowlabel_req __user *) optval)->flr_label,