Messages in this thread | | | Date | Thu, 23 Jul 2020 11:13:55 -0400 | From | Peilin Ye <> | Subject | Re: [Linux-kernel-mentees] [PATCH net] AX.25: Fix out-of-bounds read in ax25_connect() |
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On Thu, Jul 23, 2020 at 05:28:15PM +0300, Dan Carpenter wrote: > 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+c82752228ed975b0a623@syzkaller.appspotmail.com > > Link: https://syzkaller.appspot.com/bug?id=55ef9d629f3b3d7d70b69558015b63b48d01af66 > > Signed-off-by: Peilin Ye <yepeilin.cs@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.
Thank you for fixing this up! I did some math but I didn't think of that. Will be more careful when removing things.
Peilin Ye
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