From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from firstgate.proxmox.com (firstgate.proxmox.com [IPv6:2a01:7e0:0:424::9]) by lore.proxmox.com (Postfix) with ESMTPS id 1595F1FF141 for ; Tue, 02 Jun 2026 14:17:05 +0200 (CEST) Received: from firstgate.proxmox.com (localhost [127.0.0.1]) by firstgate.proxmox.com (Proxmox) with ESMTP id 1D126123E5; Tue, 2 Jun 2026 14:17:03 +0200 (CEST) From: Dominik Csapak To: pve-devel@lists.proxmox.com Subject: [PATCH qemu-server v2] fix #7654: prevent use after free Date: Tue, 2 Jun 2026 14:16:12 +0200 Message-ID: <20260602121659.2497188-1-d.csapak@proxmox.com> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-SPAM-LEVEL: Spam detection results: 0 AWL 0.049 Adjusted score from AWL reputation of From: address BAYES_00 -1.9 Bayes spam probability is 0 to 1% DMARC_MISSING 0.1 Missing DMARC policy KAM_DMARC_STATUS 0.01 Test Rule for DKIM or SPF Failure with Strict Alignment SPF_HELO_NONE 0.001 SPF: HELO does not publish an SPF Record SPF_PASS -0.001 SPF: sender matches SPF record Message-ID-Hash: QJIC54ACS7DFWHGIZ5NJ2NHEASASF7GM X-Message-ID-Hash: QJIC54ACS7DFWHGIZ5NJ2NHEASASF7GM X-MailFrom: d.csapak@proxmox.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; loop; banned-address; emergency; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header X-Mailman-Version: 3.3.10 Precedence: list List-Id: Proxmox VE development discussion List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: to prevent a use after free on a client struct, instead of freeing it inline in 'cleanup_client', only set a boolean flag 'pending_free' and free it in the main 'handle_client' function. the call graphs look like this: handle_client `-> cleanup_client `-> handle_qmp_handshake `-> cleanup_client `-> send_qmp_cmd `-> cleanup_client `-> handle_qmp_event `-> terminate_check `-> send_qmp_cmd `-> cleanup_client `-> handle_qmp_return `-> terminate_check `-> send_qmp_cmd `-> cleanup_client In addition, if we cleanup a 'vzdump' client, the corresponding VM client will be looked up and 'terminate_check' will be called for it. If that resulted in a cleanup, we have to free that immediately. cleanup_client will not be called in other paths, so handling the freeing in handle_client should suffice. Signed-off-by: Dominik Csapak Reviewed-by: Fiona Ebner --- changes from v1: * picked up r-b trailer from fiona (thanks!) * fixed commit message typo and nits src/qmeventd/qmeventd.c | 17 ++++++++++++++++- src/qmeventd/qmeventd.h | 1 + 2 files changed, 17 insertions(+), 1 deletion(-) diff --git a/src/qmeventd/qmeventd.c b/src/qmeventd/qmeventd.c index 1d9eb74a..5c873e88 100644 --- a/src/qmeventd/qmeventd.c +++ b/src/qmeventd/qmeventd.c @@ -405,6 +405,13 @@ void cleanup_client(struct Client *client) { VERBOSE_PRINT("%s: backup ended\n", client->vzdump.vmid); vmc->qemu.backup = false; terminate_check(vmc); + + // we cleaned up a vm client while handling a vzdump client, so we + // have to free it here directly. the nested cleanup call must have + // removed it from the vm_clients hash table already in that case. + if (vmc->pending_free) { + free(vmc); + } } break; @@ -418,7 +425,7 @@ void cleanup_client(struct Client *client) { } VERBOSE_PRINT("removing %s from forced cleanups\n", client->qemu.vmid); forced_cleanups = g_slist_remove(forced_cleanups, client); - free(client); + client->pending_free = true; } void terminate_client(struct Client *client) { @@ -478,11 +485,13 @@ void handle_client(struct Client *client) { if (!(errno == EAGAIN || errno == EWOULDBLOCK)) { log_neg((int)len, "read"); cleanup_client(client); + free(client); } return; } else if (len == 0) { VERBOSE_PRINT("pid%d: got EOF\n", client->pid); cleanup_client(client); + free(client); return; } @@ -530,6 +539,12 @@ void handle_client(struct Client *client) { break; } json_object_put(jobj); + + // if the client was cleaned up, we have to free it here + if (client->pending_free) { + free(client); + break; + } } json_tokener_free(tok); } diff --git a/src/qmeventd/qmeventd.h b/src/qmeventd/qmeventd.h index bb372077..6a293b84 100644 --- a/src/qmeventd/qmeventd.h +++ b/src/qmeventd/qmeventd.h @@ -66,6 +66,7 @@ struct Client { pid_t pid; int pidfd; time_t timeout; + bool pending_free; ClientType type; ClientState state; -- 2.47.3