From 31642e7089df8fd3f54ca7843f7ee2952978cad1 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 24 May 2023 14:14:56 +0000 Subject: netrom: fix info-leak in nr_write_internal() Simon Kapadia reported the following issue: The Online Amateur Radio Community (OARC) has recently been experimenting with building a nationwide packet network in the UK. As part of our experimentation, we have been testing out packet on 300bps HF, and playing with net/rom. For HF packet at this baud rate you really need to make sure that your MTU is relatively low; AX.25 suggests a PACLEN of 60, and a net/rom PACLEN of 40 to go with that. However the Linux net/rom support didn't work with a low PACLEN; the mkiss module would truncate packets if you set the PACLEN below about 200 or so, e.g.: Apr 19 14:00:51 radio kernel: [12985.747310] mkiss: ax1: truncating oversized transmit packet! This didn't make any sense to me (if the packets are smaller why would they be truncated?) so I started investigating. I looked at the packets using ethereal, and found that many were just huge compared to what I would expect. A simple net/rom connection request packet had the request and then a bunch of what appeared to be random data following it: Simon provided a patch that I slightly revised: Not only we must not use skb_tailroom(), we also do not want to count NR_NETWORK_LEN twice. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Co-Developed-by: Simon Kapadia Signed-off-by: Simon Kapadia Signed-off-by: Eric Dumazet Tested-by: Simon Kapadia Reviewed-by: Simon Horman Link: https://lore.kernel.org/r/20230524141456.1045467-1-edumazet@google.com Signed-off-by: Jakub Kicinski --- net/netrom/nr_subr.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) (limited to 'net/netrom') diff --git a/net/netrom/nr_subr.c b/net/netrom/nr_subr.c index 3f99b432ea70..e2d2af924cff 100644 --- a/net/netrom/nr_subr.c +++ b/net/netrom/nr_subr.c @@ -123,7 +123,7 @@ void nr_write_internal(struct sock *sk, int frametype) unsigned char *dptr; int len, timeout; - len = NR_NETWORK_LEN + NR_TRANSPORT_LEN; + len = NR_TRANSPORT_LEN; switch (frametype & 0x0F) { case NR_CONNREQ: @@ -141,7 +141,8 @@ void nr_write_internal(struct sock *sk, int frametype) return; } - if ((skb = alloc_skb(len, GFP_ATOMIC)) == NULL) + skb = alloc_skb(NR_NETWORK_LEN + len, GFP_ATOMIC); + if (!skb) return; /* @@ -149,7 +150,7 @@ void nr_write_internal(struct sock *sk, int frametype) */ skb_reserve(skb, NR_NETWORK_LEN); - dptr = skb_put(skb, skb_tailroom(skb)); + dptr = skb_put(skb, len); switch (frametype & 0x0F) { case NR_CONNREQ: -- cgit v1.2.3