From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 587C73B840B for ; Fri, 4 Sep 2026 15:59:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788537580; cv=none; b=L0zsWKynZM06lMcWeiuYJwEmxT7xFkdORKMxOoa43or3IovqD0rQZlB8cMUkfWfTR/WdVNp+Jg2Jr0c79jshHRNggMY7UeTBdj76Qc0PxSUnrIMZ0pPOzaI9GHjDe14IJspIx8aMsSQU9/4BVne7DmxB/Ot8Io8YV7qiM0SPKaM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788537580; c=relaxed/simple; bh=slJ2zNT5C+QE5Jxxw/c+6GaI2p8IuNo7ajDO03MAEhg=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=caUc+GrsXi0Y3oAZ8YpwmVeAmNq+59MvGLD7/PnL9X8qe/ZthMSmAtXS8vBmijBMFpPrjVp8FIy7uvwCkJkGxJDNvjOmdZ9LzJo7IszJRHQVCHOBnEy2eyOQ8JSaJAAFL7v6rjmSdjO8Jrt7sFyB0AIUwvK9MI0wJPCu02y4f9I= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=YLXgLRAc; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="YLXgLRAc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4E3181F0156F; Fri, 4 Sep 2026 15:59:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1788537579; bh=m8D3bMM/m+LOtQkHjR0I/Bq4MlEwU4EqRQmPeRZGEBI=; h=From:To:Cc:Subject:Date:Reply-To; b=YLXgLRAcSNI0lF7wvg4UxiSsTi9rjp8DM0mXIpVgMampm4+QBDFzma0m/I+PHplEq voFkAaYML+7jwsIM4kzvlxlpZH+ucivCVoKR+qU7miXWS8AmLUsdNCln8xA29QQC4J aXnqal75ZdI8oAPByezh70rKGH3mPBatppMcuuGI= From: Greg Kroah-Hartman To: linux-cve-announce@vger.kernel.org Cc: Greg Kroah-Hartman Subject: CVE-2026-80842: net: bridge: mcast: fix use-after-free of a master VLAN's multicast context Date: Fri, 4 Sep 2026 17:53:09 +0200 Message-ID: <2026090458-CVE-2026-80842-d74a@gregkh> X-Mailer: git-send-email 2.55.0 Reply-To: , Precedence: bulk X-Mailing-List: linux-cve-announce@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=5158; i=gregkh@linuxfoundation.org; h=from:subject:message-id; bh=B6C/Q2pO4HNo9y6duvRb/JFlFWCHPLFASXhmIyM1SqY=; b=owGbwMvMwCRo6H6F97bub03G02pJDFmzXkZd/16dWtAV1Cnqc1/4e8nfiP2xTdOU5fiFTB6IL w9ic7HriGVhEGRikBVTZPmyjefo/opDil6Gtqdh5rAygQxh4OIUgIkYODEsOHZyNs+FPr4btatz Pz1bpFQ1z1/UjWHBxvevHST+Wsk8qDu5MifQNvV/vNx7AA== X-Developer-Key: i=gregkh@linuxfoundation.org; a=openpgp; fpr=F4B60CC5BF78C2214A313DCB3147D40DDB2DFB29 Content-Transfer-Encoding: 8bit From: Greg Kroah-Hartman Description =========== In the Linux kernel, the following vulnerability has been resolved: net: bridge: mcast: fix use-after-free of a master VLAN's multicast context br_multicast_toggle_one_vlan() clears BR_VLFLAG_MCAST_ENABLED under br->multicast_lock before stopping a VLAN's multicast context. That is the teardown handshake: lockless readers gate on the flag through br_multicast_ctx_should_use() -> br_multicast_ctx_vlan_disabled(), so once it is cleared under the lock no reader can arm the context again. For a master VLAN the handshake never runs. __vlan_del() clears BRIDGE_VLAN_INFO_BRENTRY before calling br_vlan_put_master(), so br_multicast_toggle_one_vlan(masterv, false) returns early on !br_vlan_is_brentry(vlan): the flag stays set and br->multicast_lock is never taken. br_vlan_put_master() then drains the context in br_multicast_ctx_deinit() and frees the VLAN through call_rcu(), while a reader still inside rcu_read_lock() sees the context as enabled and re-arms it. The port and port-VLAN branch of the function has no br_vlan_is_brentry() test and flips the flag under br->multicast_lock, so it is not affected. The reader is the bridge transmit path. For a master VLAN br_multicast_rcv() selects brmctx = &vlan->br_mcast_ctx with pmctx = NULL, so IGMP sent to the bridge device re-arms the context's timers after br_multicast_ctx_deinit() has already stopped them. BUG: KASAN: slab-use-after-free in detach_if_pending+0x412/0x4a0 Write of size 8 at addr ffff88810ac39918 by task brmc/601 __mod_timer+0x51a/0xc50 br_multicast_host_join+0x25b/0x390 __br_multicast_add_group+0x468/0x530 br_ip4_multicast_add_group+0x1a0/0x260 br_multicast_rcv+0x2cda/0x61e0 br_dev_xmit+0x6c4/0x1540 Allocated by task 610: br_vlan_add+0x111/0xb40 br_vlan_info+0x370/0x3e0 Freed by task 0: kfree+0x1a7/0x4f0 rcu_core+0x7dc/0x10a0 Only test br_vlan_is_brentry() when enabling, like the br_multicast_ctx_vlan_global_disabled() test next to it. Disabling then always clears BR_VLFLAG_MCAST_ENABLED under br->multicast_lock before br_multicast_ctx_deinit() drains the context. The Linux kernel CVE team has assigned CVE-2026-80842 to this issue. Affected and fixed versions =========================== Issue introduced in 5.15 with commit 7b54aaaf53cb784411426c64482af0435f7c845e and fixed in 5.15.220 with commit 3afaaee2f972aec9059110953adb62fa3cf5c4bd Issue introduced in 5.15 with commit 7b54aaaf53cb784411426c64482af0435f7c845e and fixed in 6.1.187 with commit 22226a2c3b90f15b0925f1464470d3baa6c5677e Issue introduced in 5.15 with commit 7b54aaaf53cb784411426c64482af0435f7c845e and fixed in 6.6.156 with commit 7c54fd8cfbcf371a5ef50db5c53fe6e85fb76686 Issue introduced in 5.15 with commit 7b54aaaf53cb784411426c64482af0435f7c845e and fixed in 6.12.108 with commit 3a0ad4fcdfa0b7dba1876de14a12cb65c8b5ca50 Issue introduced in 5.15 with commit 7b54aaaf53cb784411426c64482af0435f7c845e and fixed in 6.18.49 with commit c069f29da72324697aa4b7cab5b3647a7d24a575 Issue introduced in 5.15 with commit 7b54aaaf53cb784411426c64482af0435f7c845e and fixed in 7.1.13 with commit 3f4752996735e0628af559aa8da1d872c2fac13b Issue introduced in 5.15 with commit 7b54aaaf53cb784411426c64482af0435f7c845e and fixed in 7.2.3 with commit 57f94d3f4dee8b54d63cefddf1112be4656ef9e6 Issue introduced in 5.15 with commit 7b54aaaf53cb784411426c64482af0435f7c845e and fixed in 7.3-rc1 with commit 50e5c6605cc9c2dd57bd2d1b3459674d19738983 Please see https://www.kernel.org for a full list of currently supported kernel versions by the kernel community. Unaffected versions might change over time as fixes are backported to older supported kernel versions. The official CVE entry at https://cve.org/CVERecord/?id=CVE-2026-80842 will be updated if fixes are backported, please check that for the most up to date information about this issue. Affected files ============== The file(s) affected by this issue are: net/bridge/br_multicast.c Mitigation ========== The Linux kernel CVE team recommends that you update to the latest stable kernel version for this, and many other bugfixes. Individual changes are never tested alone, but rather are part of a larger kernel release. Cherry-picking individual commits is not recommended or supported by the Linux kernel community at all. If however, updating to the latest release is impossible, the individual changes to resolve this issue can be found at these commits: https://git.kernel.org/stable/c/3afaaee2f972aec9059110953adb62fa3cf5c4bd https://git.kernel.org/stable/c/22226a2c3b90f15b0925f1464470d3baa6c5677e https://git.kernel.org/stable/c/7c54fd8cfbcf371a5ef50db5c53fe6e85fb76686 https://git.kernel.org/stable/c/3a0ad4fcdfa0b7dba1876de14a12cb65c8b5ca50 https://git.kernel.org/stable/c/c069f29da72324697aa4b7cab5b3647a7d24a575 https://git.kernel.org/stable/c/3f4752996735e0628af559aa8da1d872c2fac13b https://git.kernel.org/stable/c/57f94d3f4dee8b54d63cefddf1112be4656ef9e6 https://git.kernel.org/stable/c/50e5c6605cc9c2dd57bd2d1b3459674d19738983