From: Eric Dumazet <edumazet@xxxxxxxxxx>
[ Upstream commit 31642e7089df8fd3f54ca7843f7ee2952978cad1 ]
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@xxxxxxxxxx>
Signed-off-by: Simon Kapadia <szymon@xxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Tested-by: Simon Kapadia <szymon@xxxxxxxxxx>
Reviewed-by: Simon Horman <simon.horman@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230524141456.1045467-1-edumazet@xxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
net/netrom/nr_subr.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/net/netrom/nr_subr.c b/net/netrom/nr_subr.c
index 3f99b432ea707..e2d2af924cff4 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:
--
2.39.2
