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ipv6: mcast: add RCU protection to mld_newpack()

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mld_newpack() can be called without RTNL or RCU being held.

Note that we no longer can use sock_alloc_send_skb() because
ipv6.igmp_sk uses GFP_KERNEL allocations which can sleep.

Instead use alloc_skb() and charge the net->ipv6.igmp_sk
socket under RCU protection.

Fixes: b8ad0cbc58 ("[NETNS][IPV6] mcast - handle several network namespace")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20250212141021.1663666-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet 2025-02-12 14:10:21 +00:00 • committed by Jakub Kicinski
parent 5bef3ac184
commit a527750d87
1 changed files with 10 additions and 4 deletions
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14
net/ipv6/mcast.c
View file

@ -1773,21 +1773,19 @@ static struct sk_buff *mld_newpack(struct inet6_dev *idev, unsigned int mtu)
struct net_device *dev = idev->dev;
int hlen = LL_RESERVED_SPACE(dev);
int tlen = dev->needed_tailroom;
struct net *net = dev_net(dev);
const struct in6_addr *saddr;
struct in6_addr addr_buf;
struct mld2_report *pmr;
struct sk_buff *skb;
unsigned int size;
struct sock *sk;
int err;
struct net *net;
sk = net->ipv6.igmp_sk;
/* we assume size > sizeof(ra) here
* Also try to not allocate high-order pages for big MTU
*/
size = min_t(int, mtu, PAGE_SIZE / 2) + hlen + tlen;
skb = sock_alloc_send_skb(sk, size, 1, &err);
skb = alloc_skb(size, GFP_KERNEL);
if (!skb)
return NULL;
@ -1795,6 +1793,12 @@ static struct sk_buff *mld_newpack(struct inet6_dev *idev, unsigned int mtu)
skb_reserve(skb, hlen);
skb_tailroom_reserve(skb, mtu, tlen);
rcu_read_lock();
net = dev_net_rcu(dev);
sk = net->ipv6.igmp_sk;
skb_set_owner_w(skb, sk);
if (ipv6_get_lladdr(dev, &addr_buf, IFA_F_TENTATIVE)) {
/* <draft-ietf-magma-mld-source-05.txt>:
* use unspecified address as the source address
@ -1806,6 +1810,8 @@ static struct sk_buff *mld_newpack(struct inet6_dev *idev, unsigned int mtu)
ip6_mc_hdr(sk, skb, dev, saddr, &mld2_all_mcr, NEXTHDR_HOP, 0);
rcu_read_unlock();
skb_put_data(skb, ra, sizeof(ra));
skb_set_transport_header(skb, skb_tail_pointer(skb) - skb->data);