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authorEric Dumazet <edumazet@google.com>2023-05-24 17:14:56 +0300
committerJakub Kicinski <kuba@kernel.org>2023-05-26 07:02:29 +0300
commit31642e7089df8fd3f54ca7843f7ee2952978cad1 (patch)
treee0c1b0669ada69fc25856ac95eeec8bf29c4b4f6 /net/netrom
parentffb3322181d9e8db880202e4f00991764a35d812 (diff)
downloadlinux-31642e7089df8fd3f54ca7843f7ee2952978cad1.tar.xz
netrom: fix info-leak in nr_write_internal()
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: 1da177e4c3f4 ("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>
Diffstat (limited to 'net/netrom')
-rw-r--r--net/netrom/nr_subr.c7
1 files changed, 4 insertions, 3 deletions
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: