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 CD0673C0635; Thu, 10 Sep 2026 10:19:57 +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=1789035599; cv=none; b=g94ic0GTBgYtWTD3D7tgp78lEH6TSAFXTPVuNDF4gcrd7meMVUmPcY9tKkPj28sF4Mo49cy8QbzNbmkAmdaNTG/BWi/+ZXiSD+13Dvumgif/YP4ahCT905fpcWjfowLKAh8NxfzVDWhscDZITDreCVIcemwUn1A7E8DFi0eveiA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789035599; c=relaxed/simple; bh=AGMXOz9WooLtmxCka5jf4X5QiuyLIh02VQs1iSo0TnA=; h=From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type:Date; b=KKUieZI2zMQ2GVJFL2KWJAE06rDFPUDCx8Dw6qmLqPMBHkc1+sedbIeBSYAC4hHeAg8y9uQ0CZv2lNVFr5Bhh1EBHOGZVHCtbTzsxJRJdwkwY4g4tNURIs2klxSBOtBc4uuStrZRS8V+EPzW40Nxs3ktTxGyvJbnTaeWrHnavPE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Mwp/OYZ+; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Mwp/OYZ+" Received: by smtp.kernel.org (Postfix) with UTF8SMTPSA id E85261F000FF; Thu, 10 Sep 2026 10:19:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789035597; bh=1td4zs8wZKlsu/Ec/TS1O57yTzxpXdAFyxHvF+VC3sE=; h=From:To:Cc:Subject:Date; b=Mwp/OYZ+jSKHM/OkdunoCw336mPjlitqLIODgIYIR/EV/Oud6w1dYZjb2f+txl6zA njkUaSgRFgnFjlSYlVxha3EUTr8kTJsSnxldUJa6stxfmwWuX+eyeBS+1V09cAa8ug vsJsjpKdl8BW4HPlfBYRd5ygOd8ipFnLeaP39jM5U8dwSTj0fb+S1is56rWFBCG93E hhhHOHcIxZjG99GMlnF4RafvjI4OWpRXHP1i32c8JcX/1aycpzgMKCcVY6lTKivgqu MNq02pH3990xDjcTbci5SLxINHvkjz34FclzT6uqcjV5l3uJWh3wWvRCOACFKVfkSV 1iVkVsZib509g== From: "syzbot" To: syzkaller-bugs@googlegroups.com, Krystian Kaniewski , "Jens Axboe" , , "Nilay Shroff" Cc: linux-kernel@vger.kernel.org, syzbot@lists.linux.dev Subject: [PATCH] blk-mq: fix out-of-bounds read in blk_mq_free_rqs Message-ID: Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Date: Thu, 10 Sep 2026 10:19:56 +0000 (UTC) From: Krystian Kaniewski A KASAN slab-out-of-bounds read can occur in blk_mq_free_rqs() when there is a mismatch between the number of hardware queues allocated for the IO scheduler (et->nr_hw_queues) and the number of hardware queues in the block tag set (set->nr_hw_queues). This mismatch can happen if blk_mq_update_nr_hw_queues() fails halfway through (e.g., due to memory pressure during blk_mq_prealloc_tag_set_tags()). In this error path, the elevator is restored with a larger number of hardware queues than the block tag set actually has. When the elevator is later freed, blk_mq_free_sched_tags() iterates up to the new et->nr_hw_queues and calls blk_mq_free_rqs(). In blk_mq_free_rqs(), it attempts to access set->tags[hctx_idx] to get the driver tags. Because set->nr_hw_queues was not updated due to the earlier failure, set->tags still has the old (smaller) size, leading to an out-of-bounds read. BUG: KASAN: slab-out-of-bounds in blk_mq_free_rqs+0xde/0x680 Read of size 8 at addr ffff88818d67fc28 by task syz-executor117/5839 Call Trace: blk_mq_free_rqs+0xde/0x680 blk_mq_free_map_and_rqs+0x40/0xf0 blk_mq_free_sched_tags blk_mq_free_sched_res+0xeb/0x280 elevator_change_done+0x1d2/0x5c0 elevator_change+0x34f/0x480 elv_iosched_store+0x504/0x630 queue_attr_store+0x207/0x2b0 To fix this, explicitly check if hctx_idx < set->nr_hw_queues before accessing set->tags[hctx_idx]. If hctx_idx >= set->nr_hw_queues, the hardware queue doesn't exist in the tag set, meaning there are no driver tags to clear mappings from. In this case, safely set drv_tags to NULL. The subsequent call to blk_mq_clear_rq_mapping() already handles a NULL drv_tags pointer and will safely return. This fix also prevents a similar out-of-bounds read in the failure path of blk_mq_alloc_rqs(), where a failure during new driver tag allocation could lead to blk_mq_free_rqs() being called with an hctx_idx greater than or equal to set->nr_hw_queues. Fixes: 04225d13aef1 ("block: fix potential deadlock while running nr_hw_queue update") Assisted-by: Gemini:gemini-3.5-flash Gemini:gemini-3.1-pro-preview syzbot Reported-by: syzbot+e90526cab23b9efcd03c@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=e90526cab23b9efcd03c Link: https://syzkaller.appspot.com/ai_job?id=827b5760-86a0-4f44-9c69-430b572eac12 Signed-off-by: Krystian Kaniewski --- diff --git a/block/blk-mq.c b/block/blk-mq.c index 2c850330a..8e6726b37 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -3473,8 +3473,10 @@ void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags, if (blk_mq_is_shared_tags(set->flags)) drv_tags = set->shared_tags; - else + else if (hctx_idx < set->nr_hw_queues) drv_tags = set->tags[hctx_idx]; + else + drv_tags = NULL; if (tags->static_rqs && set->ops->exit_request) { int i; base-commit: 075b74841bd0065a3bda3440873c747938e69b68 -- See https://goo.gle/syzbot-ai-patches for information about AI-generated patches. The person who has signed off on the patch is responsible for addressing comments. syzbot engineers can be reached at syzkaller@googlegroups.com.