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From dd7511a6effe839c73ed8f71ceaa3c53f16ebdbd Mon Sep 17 00:00:00 2001
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From: Eric Blake <eblake@redhat.com>
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Date: Wed, 13 Dec 2017 18:17:30 +0100
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Subject: [PATCH 5/6] nbd/server: CVE-2017-15118 Stack smash on large export
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name
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RH-Author: Eric Blake <eblake@redhat.com>
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Message-id: <20171213181730.1278-3-eblake@redhat.com>
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Patchwork-id: 78393
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O-Subject: [RHEV-7.5 qemu-kvm-rhev PATCH 2/2] nbd/server: CVE-2017-15118 Stack smash on large export name
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Bugzilla: 1516545 1518548
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CVE: CVE-2017-15118/20171128
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RH-Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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RH-Acked-by: John Snow <jsnow@redhat.com>
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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Introduced in commit f37708f6b8 (2.10). The NBD spec says a client
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can request export names up to 4096 bytes in length, even though
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they should not expect success on names longer than 256. However,
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qemu hard-codes the limit of 256, and fails to filter out a client
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that probes for a longer name; the result is a stack smash that can
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potentially give an attacker arbitrary control over the qemu
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process.
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The smash can be easily demonstrated with this client:
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$ qemu-io f raw nbd://localhost:10809/$(printf %3000d 1 | tr ' ' a)
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If the qemu NBD server binary (whether the standalone qemu-nbd, or
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the builtin server of QMP nbd-server-start) was compiled with
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-fstack-protector-strong, the ability to exploit the stack smash
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into arbitrary execution is a lot more difficult (but still
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theoretically possible to a determined attacker, perhaps in
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combination with other CVEs). Still, crashing a running qemu (and
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losing the VM) is bad enough, even if the attacker did not obtain
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full execution control.
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CC: qemu-stable@nongnu.org
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Signed-off-by: Eric Blake <eblake@redhat.com>
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(cherry picked from commit 51ae4f8455c9e32c54770c4ebc25bf86a8128183)
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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nbd/server.c | 4 ++++
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1 file changed, 4 insertions(+)
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diff --git a/nbd/server.c b/nbd/server.c
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index b93cb88..56aed3a 100644
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--- a/nbd/server.c
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+++ b/nbd/server.c
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@@ -393,6 +393,10 @@ static int nbd_negotiate_handle_info(NBDClient *client, uint32_t length,
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msg = "name length is incorrect";
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goto invalid;
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}
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+ if (namelen >= sizeof(name)) {
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+ msg = "name too long for qemu";
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+ goto invalid;
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+ }
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if (nbd_read(client->ioc, name, namelen, errp) < 0) {
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return -EIO;
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}
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--
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1.8.3.1
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