[PATCH net] igmp: limit igmpv3_newpack() packet size to IP_MAX_MTU

[PATCH net] igmp: limit igmpv3_newpack() packet size to IP_MAX_MTU

[Eric Dumazet]

This is a follow up of commit 915d975b2ffa ("net: deal with integer
overflows in kmalloc_reserve()") based on David Laight feedback.

Back in 2010, I failed to realize malicious users could set dev->mtu
to arbitrary values. This mtu has been since limited to 0x7fffffff but
regardless of how big dev->mtu is, it makes no sense for igmpv3_newpack()
to allocate more than IP_MAX_MTU and risk various skb fields overflows.

Fixes: 57e1ab6eaddc ("igmp: refine skb allocations")
Link: https://lore.kernel.org/netdev/d273628df80f45428e739274ab9ecb72@AcuMS.aculab.com/
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: David Laight <David.Laight@ACULAB.COM>
Cc: Kyle Zeng <zengyhkyle@gmail.com>
---
 net/ipv4/igmp.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index 0c9e768e5628b1c8fd7e87bebe528762ea4a6e1e..418e5fb58fd3f2443f3c88fde5c0776805a832ef 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -353,8 +353,9 @@ static struct sk_buff *igmpv3_newpack(struct net_device *dev, unsigned int mtu)
 	struct flowi4 fl4;
 	int hlen = LL_RESERVED_SPACE(dev);
 	int tlen = dev->needed_tailroom;
-	unsigned int size = mtu;
+	unsigned int size;
 
+	size = min(mtu, IP_MAX_MTU);
 	while (1) {
 		skb = alloc_skb(size + hlen + tlen,
 				GFP_ATOMIC | __GFP_NOWARN);
-- 
2.42.0.283.g2d96d420d3-goog

Re: [PATCH net] igmp: limit igmpv3_newpack() packet size to IP_MAX_MTU

[Simon Horman]

On Tue, Sep 05, 2023 at 04:23:38AM +0000, Eric Dumazet wrote:
> This is a follow up of commit 915d975b2ffa ("net: deal with integer
> overflows in kmalloc_reserve()") based on David Laight feedback.
> 
> Back in 2010, I failed to realize malicious users could set dev->mtu
> to arbitrary values. This mtu has been since limited to 0x7fffffff but
> regardless of how big dev->mtu is, it makes no sense for igmpv3_newpack()
> to allocate more than IP_MAX_MTU and risk various skb fields overflows.
> 
> Fixes: 57e1ab6eaddc ("igmp: refine skb allocations")
> Link: https://lore.kernel.org/netdev/d273628df80f45428e739274ab9ecb72@AcuMS.aculab.com/
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Reported-by: David Laight <David.Laight@ACULAB.COM>
> Cc: Kyle Zeng <zengyhkyle@gmail.com>

Reviewed-by: Simon Horman <horms@kernel.org>

Re: [PATCH net] igmp: limit igmpv3_newpack() packet size to IP_MAX_MTU

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by David S. Miller <davem@davemloft.net>:

On Tue,  5 Sep 2023 04:23:38 +0000 you wrote:
> This is a follow up of commit 915d975b2ffa ("net: deal with integer
> overflows in kmalloc_reserve()") based on David Laight feedback.
> 
> Back in 2010, I failed to realize malicious users could set dev->mtu
> to arbitrary values. This mtu has been since limited to 0x7fffffff but
> regardless of how big dev->mtu is, it makes no sense for igmpv3_newpack()
> to allocate more than IP_MAX_MTU and risk various skb fields overflows.
> 
> [...]

Here is the summary with links:
  - [net] igmp: limit igmpv3_newpack() packet size to IP_MAX_MTU
    https://git.kernel.org/netdev/net/c/c3b704d4a4a2

You are awesome, thank you!
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