Re: [PATCH net] ipv4: provide stronger user input validation in nl_fib_input()

[David Miller]

From: Eric Dumazet 
Date: Tue, 21 Mar 2017 19:22:28 -0700

> From: Eric Dumazet 
> 
> Alexander reported a KMSAN splat caused by reads of uninitialized
> field (tb_id_in) from user provided struct fib_result_nl
> 
> It turns out nl_fib_input() sanity tests on user input is a bit
> wrong :
> 
> User can pretend nlh->nlmsg_len is big enough, but provide
> at sendmsg() time a too small buffer.
> 
> Reported-by: Alexander Potapenko 
> Signed-off-by: Eric Dumazet 

Applied and queued up for -stable, thanks Eric.

[PATCH net] ipv4: provide stronger user input validation in nl_fib_input()

[Eric Dumazet]

From: Eric Dumazet 

Alexander reported a KMSAN splat caused by reads of uninitialized
field (tb_id_in) from user provided struct fib_result_nl

It turns out nl_fib_input() sanity tests on user input is a bit
wrong :

User can pretend nlh->nlmsg_len is big enough, but provide
at sendmsg() time a too small buffer.

Reported-by: Alexander Potapenko 
Signed-off-by: Eric Dumazet 
---
 net/ipv4/fib_frontend.c |3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index 
42bfd08109dd78ab509493e8d2205d72845bb3eb..8f2133ffc2ff1b94871408a5f934cb938d3462b5
 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -1083,7 +1083,8 @@ static void nl_fib_input(struct sk_buff *skb)
 
net = sock_net(skb->sk);
nlh = nlmsg_hdr(skb);
-   if (skb->len < NLMSG_HDRLEN || skb->len < nlh->nlmsg_len ||
+   if (skb->len < nlmsg_total_size(sizeof(*frn)) ||
+   skb->len < nlh->nlmsg_len ||
nlmsg_len(nlh) < sizeof(*frn))
return;