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[PATCH] mm/slab: reject unsupported kmalloc sizes Cc: "Andrew Morton" , "Hao Li" , "Christoph Lameter" , "David Rientjes" , "Roman Gushchin" , "Alan Stern" , "Greg Kroah-Hartman" , , , , , To: "Harry Yoo" , "Vlastimil Babka (SUSE)" From: "Zi Yan" X-Mailer: aerc 0.22.0 References: <20260817-limit_kmalloc_size-v1-1-5bef487701cc@nvidia.com> <82f138f5-11d4-4839-94a3-c226fd982715@kernel.org> In-Reply-To: X-ClientProxiedBy: MN0PR05CA0021.namprd05.prod.outlook.com (2603:10b6:208:52c::16) To IA0PR12MB8374.namprd12.prod.outlook.com (2603:10b6:208:40e::7) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: IA0PR12MB8374:EE_|DS7PR12MB5911:EE_ X-MS-Office365-Filtering-Correlation-Id: dc1c2555-c5cf-41f1-dcda-08df03bc628c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|23010399003|7416014|376014|6133799003|10067099003|11063799006|4143699003|56012099006|22082099003|18002099003; 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physically contiguous memory for kernel >> > allocations. For requests larger than KMALLOC_MAX_CACHE_SIZE, kmalloc = uses >> > the page allocator and can only support up to KMALLOC_MAX_SIZE. For re= quest >> > sizes bigger than KMALLOC_MAX_SIZE, the page allocator can emit a WARN >> > because kmalloc allocates an order greater than MAX_PAGE_ORDER. System= s >> > with panic_on_warn=3D1 crash because of this WARN. Fix it by rejecting= any >> > kmalloc size bigger than KMALLOC_MAX_SIZE. >> >=20 >> > Fixes: aadb4bc4a1f9 ("SLUB: direct pass through of page size or higher= kmalloc requests") >> > Reported-by: syzbot+805630f1453e490427fa@syzkaller.appspotmail.com >> > Closes: https://lore.kernel.org/all/6a820ebc.9ebadd4d.20b15e.001b.GAE@= google.com/ >> > Tested-by: syzbot+805630f1453e490427fa@syzkaller.appspotmail.com >> > Signed-off-by: Zi Yan >> > Cc: stable@vger.kernel.org >> > --- >> > It fixes a page allocator warning (order > MAX_PAGE_ORDER) when gadget= fs >> > requests excessively large memory from kmalloc. Instead of adding >> > __GFP_NOWARN to suppress the warning, as was done for usbfs[1], change >> > kmalloc to return NULL without a warning for this specific issue. >> >=20 >> > [1] commit 4f2629ea67e72 ("USB: usbfs: Don't WARN about excessively la= rge memory allocations") >>=20 >> So I checked and for kvmalloc() we have in __kvmalloc_node_noprof() >>=20 >> /* Don't even allow crazy sizes */ >> if (unlikely(size > INT_MAX)) { >> WARN_ON_ONCE(!(flags & __GFP_NOWARN)); >> return NULL; >> } >>=20 >> This comes from Linus in commit 7661809d493b4. I'd do the same thing her= e >> then. > > But the purpose of this patch is to avoid the warning in the page > allocator. Should we fix this in the caller (gadgetfs) then?=20 It is fixed by: https://lore.kernel.org/all/20260820223719.A4A3C1F000E9@smt= p.kernel.org/ Please disregard this patch, but we can keep the discussion going. > >> Thus there would be a useful warning for e.g. development mistakes >> resulting in the size to be unexpectedly high. >>=20 >> Callers passing size that comes from userspace or similar untrusted sour= ce >> can either pass __GFP_NOWARN or sanitize the size to what they expect to= be >> sane (which is context dependent and I assume actually way lower than >> kmalloc limits in practice). Note that passing even sizes within but clo= se >> to/at the limit, trusting blindly some external source, can succeed the >> allocations but effectively DoS the system with heavy reclaim/compaction= . So >> caller sanitization should still be preferred IMHO. Some of the recent >> arguments from Linus [1] would apply to this too, I think. >>=20 >> [1] >> https://lore.kernel.org/all/CAHk-=3DwiSmgwwLKCqJwGS-dVHnSLU8W+7q1UQq-G9= =3DTBGGZbuhQ@mail.gmail.com/ --=20 Best Regards, Yan, Zi