On Thu, Jul 23, 2020 at 11:13:55AM -0400, Peilin Ye wrote:As a long-term user (25 years) of kernel ax25 I appreciate any and all efforts to improve the code (which I mostly don't understand), and I applaud those individuals rising to the task.
On Thu, Jul 23, 2020 at 05:28:15PM +0300, Dan Carpenter wrote:No problem. You had the right approach to look for ways to clean things
On Wed, Jul 22, 2020 at 11:19:01AM -0400, Peilin Ye wrote:Thank you for fixing this up! I did some math but I didn't think of
Checks on `addr_len` and `fsa->fsa_ax25.sax25_ndigis` are insufficient.The "sizeof(ax25_address) * fsa->fsa_ax25.sax25_ndigis" can have an
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@xxxxxxxxxxxxxxxxxxxxxxxxx
Link: https://syzkaller.appspot.com/bug?id=55ef9d629f3b3d7d70b69558015b63b48d01af66
Signed-off-by: Peilin Ye <yepeilin.cs@xxxxxxxxx>
---
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) {
integer overflow so you still need the
"fsa->fsa_ax25.sax25_ndigis > AX25_MAX_DIGIS" check.
that. Will be more careful when removing things.
up.
Your patches make me happy because you're trying to fix important bugs.
regards,
dan carpenter