[Linux-kernel-mentees] [PATCH net] AX.25: Prevent out-of-bounds read in ax25_sendmsg()

[Peilin Ye]

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...@gmail.com>
---
 net/ax25/af_ax25.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c
index ef5bf116157a..0862fe49d434 100644
--- a/net/ax25/af_ax25.c
+++ b/net/ax25/af_ax25.c
@@ -1509,7 +1509,8 @@ static int ax25_sendmsg(struct socket *sock, struct 
msghdr *msg, size_t len)
                        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;
                        }
-- 
2.25.1