From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 40C1B13B5B3; Tue, 14 Apr 2026 05:12:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776143523; cv=none; b=jNriGLDA4iiBGLs+9R+/vLbuQQZ8FSSwK6yE3iAj+uA/wXqo19/UMojrX4ZTHbrXTD4YfALEPAZCVgOnegYAkExUYlYj6yLHARBTn3sSc5QZwL22TfZO0btNSiRK0Dq0BFDvZfMdrB99zs5fKMcsvqzO30TWAklPCKpcRgHr1R8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776143523; c=relaxed/simple; bh=1ymNdmqnY1or9+axOYo3oczwWdJzb3tphQwKkeLCLUQ=; h=Date:To:From:Subject:Message-Id; b=aeEKBBAUNE1/F6DJcdE0P+grqOurKshap7M+vVF+32Sv4I2bGaPrHKn3k1AYm5fRBh3ueYw+tCBZfcmFuMhuerV+2OpWCF8QRBS/w5PPvcE0mi9k/809/FltiI+fkvR7Dap8B9Qe2hGILHKGRkZ310bVULpimpbrzhrsA0073Eo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=tqghoyVF; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="tqghoyVF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DBAEBC19425; Tue, 14 Apr 2026 05:12:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1776143522; bh=1ymNdmqnY1or9+axOYo3oczwWdJzb3tphQwKkeLCLUQ=; h=Date:To:From:Subject:From; b=tqghoyVFEQgM8UL4H2nOFGJkRMK+ARutPTnorHOtWgQF+MseRBJ54uhwvEC1KfaSJ f8aJD5Lpk5et11pgJExHped9EU7xcKTdDkazna36rt4IZeDG0k8nsCLDynIx++sKSR YDkrfQ6IlsWaI4r5/InkKhzM1H2pze43D2bhnntA= Date: Mon, 13 Apr 2026 22:11:58 -0700 To: mm-commits@vger.kernel.org,tj@kernel.org,surenb@google.com,stable@vger.kernel.org,shakeel.butt@linux.dev,rppt@kernel.org,mhocko@suse.com,martin.lau@linux.dev,ljs@kernel.org,liam.howlett@oracle.com,josef@toxicpanda.com,inwardvessel@gmail.com,hannes@cmpxchg.org,dennisszhou@gmail.com,david@kernel.org,axboe@kernel.dk,leitao@debian.org,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-blk-cgroup-fix-use-after-free-in-cgwb_release_workfn.patch added to mm-hotfixes-unstable branch Message-Id: <20260414051201.DBAEBC19425@smtp.kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm: blk-cgroup: fix use-after-free in cgwb_release_workfn() has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-blk-cgroup-fix-use-after-free-in-cgwb_release_workfn.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-blk-cgroup-fix-use-after-free-in-cgwb_release_workfn.patch This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: Breno Leitao Subject: mm: blk-cgroup: fix use-after-free in cgwb_release_workfn() Date: Mon, 13 Apr 2026 03:09:19 -0700 cgwb_release_workfn() calls css_put(wb->blkcg_css) and then later accesses wb->blkcg_css again via blkcg_unpin_online(). If css_put() drops the last reference, the blkcg can be freed asynchronously (css_free_rwork_fn -> blkcg_css_free -> kfree) before blkcg_unpin_online() dereferences the pointer to access blkcg->online_pin, resulting in a use-after-free: BUG: KASAN: slab-use-after-free in blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367) Write of size 4 at addr ff11000117aa6160 by task kworker/71:1/531 Workqueue: cgwb_release cgwb_release_workfn Call Trace: blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367) cgwb_release_workfn (mm/backing-dev.c:629) process_scheduled_works (kernel/workqueue.c:3278 kernel/workqueue.c:3385) Freed by task 1016: kfree (./include/linux/kasan.h:235 mm/slub.c:2689 mm/slub.c:6246 mm/slub.c:6561) css_free_rwork_fn (kernel/cgroup/cgroup.c:5542) process_scheduled_works (kernel/workqueue.c:3302 kernel/workqueue.c:3385) ** Stack based on commit 66672af7a095 ("Add linux-next specific files for 20260410") I am seeing this crash sporadically in Meta fleet across multiple kernel versions. A full reproducer is available at: https://github.com/leitao/debug/blob/main/reproducers/repro_blkcg_uaf.sh (The race window is narrow. To make it easily reproducible, inject a msleep(100) between css_put() and blkcg_unpin_online() in cgwb_release_workfn(). With that delay and a KASAN-enabled kernel, the reproducer triggers the splat reliably in less than a second.) Fix this by moving blkcg_unpin_online() before css_put(), so the cgwb's CSS reference keeps the blkcg alive while blkcg_unpin_online() accesses it. Link: https://lkml.kernel.org/r/20260413-blkcg-v1-1-35b72622d16c@debian.org Fixes: 59b57717fff8 ("blkcg: delay blkg destruction until after writeback has finished") Signed-off-by: Breno Leitao Cc: David Hildenbrand Cc: Dennis Zhou Cc: Jens Axboe Cc: Johannes Weiner Cc: Josef Bacik Cc: JP Kobryn Cc: Liam Howlett Cc: Lorenzo Stoakes (Oracle) Cc: Martin KaFai Lau Cc: Michal Hocko Cc: Mike Rapoport Cc: Shakeel Butt Cc: Suren Baghdasaryan Cc: Tejun Heo Cc: Signed-off-by: Andrew Morton --- mm/backing-dev.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/mm/backing-dev.c~mm-blk-cgroup-fix-use-after-free-in-cgwb_release_workfn +++ a/mm/backing-dev.c @@ -618,12 +618,13 @@ static void cgwb_release_workfn(struct w wb_shutdown(wb); css_put(wb->memcg_css); - css_put(wb->blkcg_css); - mutex_unlock(&wb->bdi->cgwb_release_mutex); /* triggers blkg destruction if no online users left */ blkcg_unpin_online(wb->blkcg_css); + css_put(wb->blkcg_css); + mutex_unlock(&wb->bdi->cgwb_release_mutex); + fprop_local_destroy_percpu(&wb->memcg_completions); spin_lock_irq(&cgwb_lock); _ Patches currently in -mm which might be from leitao@debian.org are mm-blk-cgroup-fix-use-after-free-in-cgwb_release_workfn.patch mm-kmemleak-add-config_debug_kmemleak_verbose-build-option.patch kho-add-size-parameter-to-kho_add_subtree.patch kho-rename-fdt-parameter-to-blob-in-kho_add-remove_subtree.patch kho-persist-blob-size-in-kho-fdt.patch kho-fix-kho_in_debugfs_init-to-handle-non-fdt-blobs.patch kho-kexec-metadata-track-previous-kernel-chain.patch kho-kexec-metadata-track-previous-kernel-chain-fix.patch kho-document-kexec-metadata-tracking-feature.patch mm-vmstat-fix-vmstat_shepherd-double-scheduling-vmstat_update.patch kho-fix-error-handling-in-kho_add_subtree.patch mm-vmstat-spread-vmstat_update-requeue-across-the-stat-interval.patch