On Wed, Jul 22, 2020 at 11:19:01AM -0400, Peilin Ye wrote: > 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+c82752228ed975b0a...@syzkaller.appspotmail.com > Link: > https://syzkaller.appspot.com/bug?id=55ef9d629f3b3d7d70b69558015b63b48d01af66 > Signed-off-by: Peilin Ye <yepeilin...@gmail.com> > --- > net/ax25/af_ax25.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/net/ax25/af_ax25.c b/net/ax25/af_ax25.c > index fd91cd34f25e..ef5bf116157a 100644 > --- 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) {
The "sizeof(ax25_address) * fsa->fsa_ax25.sax25_ndigis" can have an integer overflow so you still need the "fsa->fsa_ax25.sax25_ndigis > AX25_MAX_DIGIS" check. regards, dan carpenter
