[PATCH 4.4 39/54] AX.25: Prevent out-of-bounds read in ax25_sendmsg()

Greg Kroah-Hartman
2020-07-30T08:14:04Z

From: Peilin Ye <yepeilin.cs@gmail.com>

[ Upstream commit 8885bb0621f01a6c82be60a91e5fc0f6e2f71186 ]

Checks on `addr_len` and `usax->sax25_ndigis` are insufficient.
ax25_sendmsg() can go out of bounds when `usax->sax25_ndigis` equals to 7
or 8. Fix it.

It is safe to remove `usax->sax25_ndigis > AX25_MAX_DIGIS`, since
`addr_len` is guaranteed to be less than or equal to
`sizeof(struct full_sockaddr_ax25)`

Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ax25/af_ax25.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -1512,7 +1512,8 @@ static int ax25_sendmsg(struct socket *s
struct full_sockaddr_ax25 *fsa = (struct full_sockaddr_ax25 *)usax;

/* Valid number of digipeaters ? */
- if (usax->sax25_ndigis < 1 || usax->sax25_ndigis > AX25_MAX_DIGIS) {
+ if (usax->sax25_ndigis < 1 || addr_len < sizeof(struct sockaddr_ax25) +
+ sizeof(ax25_address) * usax->sax25_ndigis) {
err = -EINVAL;
goto out;
}