AX.25: Fix out-of-bounds read in ax25_connect()

Checks on `addr_len` and `fsa->fsa_ax25.sax25_ndigis` are insufficient.
ax25_connect() can go out of bounds when `fsa->fsa_ax25.sax25_ndigis`
equals to 7 or 8. Fix it.

This issue has been reported as a KMSAN uninit-value bug, because in such
a case, ax25_connect() reaches into the uninitialized portion of the
`struct sockaddr_storage` statically allocated in __sys_connect().

It is safe to remove `fsa->fsa_ax25.sax25_ndigis > AX25_MAX_DIGIS` because
`addr_len` is guaranteed to be less than or equal to
`sizeof(struct full_sockaddr_ax25)`.

Reported-by: syzbot+c82752228ed975b0a623@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?id=55ef9d629f3b3d7d70b69558015b63b48d01af66
Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index fd91cd34f25e03d0178cbe66568ed392a7013f4e..ef5bf116157a5dd61f71473b660267af2a5b7533 100644 (file)
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -1187,7 +1187,9 @@ static int __must_check ax25_connect(struct socket *sock,
        if (addr_len > sizeof(struct sockaddr_ax25) &&
            fsa->fsa_ax25.sax25_ndigis != 0) {
                /* Valid number of digipeaters ? */
-               if (fsa->fsa_ax25.sax25_ndigis < 1 || fsa->fsa_ax25.sax25_ndigis > AX25_MAX_DIGIS) {
+               if (fsa->fsa_ax25.sax25_ndigis < 1 ||
+                   addr_len < sizeof(struct sockaddr_ax25) +
+                   sizeof(ax25_address) * fsa->fsa_ax25.sax25_ndigis) {
                        err = -EINVAL;
                        goto out_release;
                }