From 4069f8f55d070b5a1eb2bf894a517ea9fb648bbd Mon Sep 17 00:00:00 2001 From: Jon Maloy Date: Tue, 5 Mar 2024 11:36:15 -0500 Subject: [PATCH 2/3] ui/clipboard: mark type as not available when there is no data MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit RH-Author: Jon Maloy RH-MergeRequest: 353: ui/clipboard: mark type as not available when there is no data RH-Jira: RHEL-19628 RH-Acked-by: Marc-André Lureau RH-Acked-by: Gerd Hoffmann RH-Commit: [2/2] fa0edf7a362a16978e2377cf61f36ff227d186b2 (redhat/rhel/src/qemu-kvm/jons-qemu-kvm-2) JIRA: https://issues.redhat.com/browse/RHEL-19628 CVE: CVE-2023-6683 Upstream: Merged Conflicts: - The function g_memdup2() is used by this commit, but is not present in this code version. It looks safe to introduce it in a preceding commit, instead of reverting to the less safe g_memdup(), so that is what we do. - There is a second upstream commit covering this CVE: commit 9c416582611b ("ui/clipboard: add asserts for update and request") which is based on several other previous commits not present in this version. Re-applying these, or trying to adapt the code, is too intrusive and risky given that it only introduces two diagnostic asserts which are not essential for solving the CVE. We therefore omit that commit. commit 405484b29f6548c7b86549b0f961b906337aa68a Author: Fiona Ebner Date: Wed Jan 24 11:57:48 2024 +0100 ui/clipboard: mark type as not available when there is no data With VNC, a client can send a non-extended VNC_MSG_CLIENT_CUT_TEXT message with len=0. In qemu_clipboard_set_data(), the clipboard info will be updated setting data to NULL (because g_memdup(data, size) returns NULL when size is 0). If the client does not set the VNC_ENCODING_CLIPBOARD_EXT feature when setting up the encodings, then the 'request' callback for the clipboard peer is not initialized. Later, because data is NULL, qemu_clipboard_request() can be reached via vdagent_chr_write() and vdagent_clipboard_recv_request() and there, the clipboard owner's 'request' callback will be attempted to be called, but that is a NULL pointer. In particular, this can happen when using the KRDC (22.12.3) VNC client. Another scenario leading to the same issue is with two clients (say noVNC and KRDC): The noVNC client sets the extension VNC_FEATURE_CLIPBOARD_EXT and initializes its cbpeer. The KRDC client does not, but triggers a vnc_client_cut_text() (note it's not the _ext variant)). There, a new clipboard info with it as the 'owner' is created and via qemu_clipboard_set_data() is called, which in turn calls qemu_clipboard_update() with that info. In qemu_clipboard_update(), the notifier for the noVNC client will be called, i.e. vnc_clipboard_notify() and also set vs->cbinfo for the noVNC client. The 'owner' in that clipboard info is the clipboard peer for the KRDC client, which did not initialize the 'request' function. That sounds correct to me, it is the owner of that clipboard info. Then when noVNC sends a VNC_MSG_CLIENT_CUT_TEXT message (it did set the VNC_FEATURE_CLIPBOARD_EXT feature correctly, so a check for it passes), that clipboard info is passed to qemu_clipboard_request() and the original segfault still happens. Fix the issue by handling updates with size 0 differently. In particular, mark in the clipboard info that the type is not available. While at it, switch to g_memdup2(), because g_memdup() is deprecated. Cc: qemu-stable@nongnu.org Fixes: CVE-2023-6683 Reported-by: Markus Frank Suggested-by: Marc-André Lureau Signed-off-by: Fiona Ebner Reviewed-by: Marc-André Lureau Tested-by: Markus Frank Message-ID: <20240124105749.204610-1-f.ebner@proxmox.com> Signed-off-by: Jon Maloy --- ui/clipboard.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/ui/clipboard.c b/ui/clipboard.c index d7b008d62a..b8c795f2e2 100644 --- a/ui/clipboard.c +++ b/ui/clipboard.c @@ -123,9 +123,15 @@ void qemu_clipboard_set_data(QemuClipboardPeer *peer, } g_free(info->types[type].data); - info->types[type].data = g_memdup(data, size); - info->types[type].size = size; - info->types[type].available = true; + if (size) { + info->types[type].data = g_memdup2(data, size); + info->types[type].size = size; + info->types[type].available = true; + } else { + info->types[type].data = NULL; + info->types[type].size = 0; + info->types[type].available = false; + } if (update) { qemu_clipboard_update(info); -- 2.41.0