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client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C Received: from SATLEXMB04.amd.com (165.204.84.17) by CH1PEPF0000AD81.mail.protection.outlook.com (10.167.244.89) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.8511.15 via Frontend Transport; Wed, 5 Mar 2025 03:54:42 +0000 Received: from [10.252.205.52] (10.180.168.240) by SATLEXMB04.amd.com (10.181.40.145) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.39; Tue, 4 Mar 2025 21:54:37 -0600 Message-ID: <6409142e-d535-4ddd-b58d-41ea793f61b4@amd.com> Date: Wed, 5 Mar 2025 09:24:34 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] sched/fair: Fix potential memory corruption in child_cfs_rq_on_list To: Zecheng Li , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot CC: Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Josh Don , References: <20250304214031.2882646-1-zecheng@google.com> Content-Language: en-US From: K Prateek Nayak In-Reply-To: <20250304214031.2882646-1-zecheng@google.com> Content-Type: text/plain; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 05 Mar 2025 03:54:42.3057 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 62fb8a89-0659-4f04-5caf-08dd5b9975f6 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: CH1PEPF0000AD81.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR12MB9148 Hello Li, On 3/5/2025 3:10 AM, Zecheng Li wrote: > child_cfs_rq_on_list attempts to convert a 'prev' pointer to a cfs_rq. > This 'prev' pointer can originate from struct rq's leaf_cfs_rq_list, > making the conversion invalid and potentially leading to memory > corruption. Depending on the relative positions of leaf_cfs_rq_list and > the task group (tg) pointer within the struct, this can cause a memory > fault or access garbage data. > > The issue arises in list_add_leaf_cfs_rq, where both > cfs_rq->leaf_cfs_rq_list and rq->leaf_cfs_rq_list are added to the same > leaf list. Also, rq->tmp_alone_branch can be set to rq->leaf_cfs_rq_list. > > This adds a check `if (prev == &rq->leaf_cfs_rq_list)` after the main > conditional in child_cfs_rq_on_list. This ensures that the container_of > operation will convert a correct cfs_rq struct. > > This check is sufficient because only cfs_rqs on the same CPU are added > to the list, so verifying the 'prev' pointer against the current rq's list > head is enough. > > Fixes a potential memory corruption issue that due to current struct > layout might not be manifesting as a crash but could lead to unpredictable > behavior when the layout changes. > > Signed-off-by: Zecheng Li > --- > kernel/sched/fair.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 857808da23d8..9dafb374d76d 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4061,15 +4061,17 @@ static inline bool child_cfs_rq_on_list(struct cfs_rq *cfs_rq) > { > struct cfs_rq *prev_cfs_rq; > struct list_head *prev; > + struct rq *rq = rq_of(cfs_rq); > > if (cfs_rq->on_list) { > prev = cfs_rq->leaf_cfs_rq_list.prev; > } else { > - struct rq *rq = rq_of(cfs_rq); > - > prev = rq->tmp_alone_branch; > } A "SCHED_WARN_ON(prev == &rq->leaf_cfs_rq_list)" here is easily tripped during early boot on my setup before this fix. Only nit. is perhaps that return can go into the else clause above since "cfs_rq->on_list" case will guarantee a "leaf_cfs_rq_list" pointer that is embedded in a valid cfs_rq struct but I've no strong feelings. Feel free to add: Reviewed-and-tested-by: K Prateek Nayak -- Thanks and Regards, Prateek > > + if (prev == &rq->leaf_cfs_rq_list) > + return false; > + > prev_cfs_rq = container_of(prev, struct cfs_rq, leaf_cfs_rq_list); > > return (prev_cfs_rq->tg->parent == cfs_rq->tg); > > base-commit: 7ab02bd36eb444654183ad6c5b15211ddfa32a8f