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netrom: fix info-leak in nr_write_internal()

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Simon Kapadia reported the following issue:

<quote>

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:

</quote>

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: 1da177e4c3 ("Linux-2.6.12-rc2")
Co-Developed-by: Simon Kapadia <szymon@kapadia.pl>
Signed-off-by: Simon Kapadia <szymon@kapadia.pl>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Simon Kapadia <szymon@kapadia.pl>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/20230524141456.1045467-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet 2023-05-24 14:14:56 +00:00 committed by Jakub Kicinski
parent ffb3322181
commit 31642e7089
1 changed files with 4 additions and 3 deletions
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7
net/netrom/nr_subr.c
View File

@ -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: