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ipmr: Use MAXVIFS in mroute_msgsize().

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mroute_msgsize() calculates skb size needed for ipmr_fill_mroute().

The size differs based on mrt->maxvif.

We will drop RTNL for ipmr_rtm_getroute() and mrt->maxvif may
change under RCU.

To avoid -EMSGSIZE, let's calculate the size with the maximum
value of mrt->maxvif, MAXVIFS.

struct rtnexthop is 8 bytes and MAXVIFS is 32, so the maximum delta
is 256 bytes, which is small enough.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20260228221800.1082070-5-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Kuniyuki Iwashima
2026-02-28 22:17:22 +00:00
committed by Jakub Kicinski
parent 402a8111d7
commit 2bd6c9d600
1 changed files with 4 additions and 5 deletions
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9
net/ipv4/ipmr.c
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@@ -2510,7 +2510,7 @@ static int _ipmr_fill_mroute(struct mr_table *mrt, struct sk_buff *skb,
cmd, flags);
}
static size_t mroute_msgsize(bool unresolved, int maxvif)
static size_t mroute_msgsize(bool unresolved)
{
size_t len =
NLMSG_ALIGN(sizeof(struct rtmsg))
@@ -2523,7 +2523,7 @@ static size_t mroute_msgsize(bool unresolved, int maxvif)
len = len
+ nla_total_size(4) /* RTA_IIF */
+ nla_total_size(0) /* RTA_MULTIPATH */
+ maxvif * NLA_ALIGN(sizeof(struct rtnexthop))
+ MAXVIFS * NLA_ALIGN(sizeof(struct rtnexthop))
/* RTA_MFC_STATS */
+ nla_total_size_64bit(sizeof(struct rta_mfc_stats))
;
@@ -2538,8 +2538,7 @@ static void mroute_netlink_event(struct mr_table *mrt, struct mfc_cache *mfc,
struct sk_buff *skb;
int err = -ENOBUFS;
skb = nlmsg_new(mroute_msgsize(mfc->_c.mfc_parent >= MAXVIFS,
mrt->maxvif),
skb = nlmsg_new(mroute_msgsize(mfc->_c.mfc_parent >= MAXVIFS),
GFP_ATOMIC);
if (!skb)
goto errout;
@@ -2711,7 +2710,7 @@ static int ipmr_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh,
goto errout_free;
}
skb = nlmsg_new(mroute_msgsize(false, mrt->maxvif), GFP_KERNEL);
skb = nlmsg_new(mroute_msgsize(false), GFP_KERNEL);
if (!skb) {
err = -ENOBUFS;
goto errout_free;