commit 7292932d45d55c7199324ab0027cc86e8198aa22
author Nicola Murino <nicola.murino@gmail.com> Sun Dec 15 18:08:57 2024 +0100
committer Gopher Robot <gobot@golang.org> Mon Feb 24 09:39:25 2025 -0800
tree 63ca1b82732708b6d33856c2670d18acae71b2a3
parent f66f74b0a406b5f6909183531ace593857f1646c

ssh: limit the size of the internal packet queue while waiting for KEX

In the SSH protocol, clients and servers execute the key exchange to
generate one-time session keys used for encryption and authentication.
The key exchange is performed initially after the connection is
established and then periodically after a configurable amount of data.
While a key exchange is in progress, we add the received packets to an
internal queue until we receive SSH_MSG_KEXINIT from the other side.
This can result in high memory usage if the other party is slow to
respond to the SSH_MSG_KEXINIT packet, or memory exhaustion if a
malicious client never responds to an SSH_MSG_KEXINIT packet during a
large file transfer.
We now limit the internal queue to 64 packets: this means 2MB with the
typical 32KB packet size.
When the internal queue is full we block further writes until the
pending key exchange is completed or there is a read or write error.

Thanks to Yuichi Watanabe for reporting this issue.

Change-Id: I1ce2214cc16e08b838d4bc346c74c72addafaeec
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/652135
Reviewed-by: Neal Patel <nealpatel@google.com>
Auto-Submit: Gopher Robot <gobot@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>