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[178.24.249.8]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5bebbbe26desm5475428a12.11.2024.08.19.05.49.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 19 Aug 2024 05:49:57 -0700 (PDT) Message-ID: <5424dfa3-03db-4a82-a08e-fb31285774b3@redhat.com> Date: Mon, 19 Aug 2024 14:49:55 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 3/4] mm: BUG_ON to avoid NULL deference while __GFP_NOFAIL fails To: Barry Song <21cnbao@gmail.com> Cc: akpm@linux-foundation.org, linux-mm@kvack.org, 42.hyeyoo@gmail.com, cl@linux.com, hailong.liu@oppo.com, hch@infradead.org, iamjoonsoo.kim@lge.com, mhocko@suse.com, penberg@kernel.org, rientjes@google.com, roman.gushchin@linux.dev, torvalds@linux-foundation.org, urezki@gmail.com, v-songbaohua@oppo.com, vbabka@suse.cz, virtualization@lists.linux.dev, Christoph Hellwig , Lorenzo Stoakes , Kees Cook , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Jason Wang , Maxime Coquelin , "Michael S. Tsirkin" , Xuan Zhuo References: <20240817062449.21164-1-21cnbao@gmail.com> <20240817062449.21164-4-21cnbao@gmail.com> <5654b71c-1d9d-4c48-b28b-664662da8897@redhat.com> <416ac265-ced2-4f90-a347-0a256edf7fdf@redhat.com> <54a4619d-e826-465e-9a0f-0a8f37798e15@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; 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Since >>>>>>> they don't check the return, we are exposed to the security risks for NULL >>>>>>> deference. >>>>>>> >>>>>>> Though BUG_ON() is not encouraged by Linus, this is an unrecoverable >>>>>>> situation. >>>>>>> >>>>>>> Christoph Hellwig: >>>>>>> The whole freaking point of __GFP_NOFAIL is that callers don't handle >>>>>>> allocation failures. So in fact a straight BUG is the right thing >>>>>>> here. >>>>>>> >>>>>>> Vlastimil Babka: >>>>>>> It's just not a recoverable situation (WARN_ON is for recoverable >>>>>>> situations). The caller cannot handle allocation failure and at the same >>>>>>> time asked for an impossible allocation. BUG_ON() is a guaranteed oops >>>>>>> with stracktrace etc. We don't need to hope for the later NULL pointer >>>>>>> dereference (which might if really unlucky happen from a different >>>>>>> context where it's no longer obvious what lead to the allocation failing). >>>>>>> >>>>>>> Michal Hocko: >>>>>>> Linus tends to be against adding new BUG() calls unless the failure is >>>>>>> absolutely unrecoverable (e.g. corrupted data structures etc.). I am >>>>>>> not sure how he would look at simply incorrect memory allocator usage to >>>>>>> blow up the kernel. Now the argument could be made that those failures >>>>>>> could cause subtle memory corruptions or even be exploitable which might >>>>>>> be a sufficient reason to stop them early. >>>>>>> >>>>>>> Signed-off-by: Barry Song >>>>>>> Reviewed-by: Christoph Hellwig >>>>>>> Acked-by: Vlastimil Babka >>>>>>> Acked-by: Michal Hocko >>>>>>> Cc: Uladzislau Rezki (Sony) >>>>>>> Cc: Lorenzo Stoakes >>>>>>> Cc: Christoph Lameter >>>>>>> Cc: Pekka Enberg >>>>>>> Cc: David Rientjes >>>>>>> Cc: Joonsoo Kim >>>>>>> Cc: Roman Gushchin >>>>>>> Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com> >>>>>>> Cc: Linus Torvalds >>>>>>> Cc: Kees Cook >>>>>>> Cc: "Eugenio Pérez" >>>>>>> Cc: Hailong.Liu >>>>>>> Cc: Jason Wang >>>>>>> Cc: Maxime Coquelin >>>>>>> Cc: "Michael S. Tsirkin" >>>>>>> Cc: Xuan Zhuo >>>>>>> --- >>>>>>> include/linux/slab.h | 4 +++- >>>>>>> mm/page_alloc.c | 4 +++- >>>>>>> mm/util.c | 1 + >>>>>>> 3 files changed, 7 insertions(+), 2 deletions(-) >>>>>>> >>>>>>> diff --git a/include/linux/slab.h b/include/linux/slab.h >>>>>>> index c9cb42203183..4a4d1fdc2afe 100644 >>>>>>> --- a/include/linux/slab.h >>>>>>> +++ b/include/linux/slab.h >>>>>>> @@ -827,8 +827,10 @@ kvmalloc_array_node_noprof(size_t n, size_t size, gfp_t flags, int node) >>>>>>> { >>>>>>> size_t bytes; >>>>>>> >>>>>>> - if (unlikely(check_mul_overflow(n, size, &bytes))) >>>>>>> + if (unlikely(check_mul_overflow(n, size, &bytes))) { >>>>>>> + BUG_ON(flags & __GFP_NOFAIL); >>>>>>> return NULL; >>>>>>> + } >>>>>>> >>>>>>> return kvmalloc_node_noprof(bytes, flags, node); >>>>>>> } >>>>>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>>>>>> index 60742d057b05..d2c37f8f8d09 100644 >>>>>>> --- a/mm/page_alloc.c >>>>>>> +++ b/mm/page_alloc.c >>>>>>> @@ -4668,8 +4668,10 @@ struct page *__alloc_pages_noprof(gfp_t gfp, unsigned int order, >>>>>>> * There are several places where we assume that the order value is sane >>>>>>> * so bail out early if the request is out of bound. >>>>>>> */ >>>>>>> - if (WARN_ON_ONCE_GFP(order > MAX_PAGE_ORDER, gfp)) >>>>>>> + if (WARN_ON_ONCE_GFP(order > MAX_PAGE_ORDER, gfp)) { >>>>>>> + BUG_ON(gfp & __GFP_NOFAIL); >>>>>>> return NULL; >>>>>>> + } >>>>>>> >>>>>>> gfp &= gfp_allowed_mask; >>>>>>> /* >>>>>>> diff --git a/mm/util.c b/mm/util.c >>>>>>> index ac01925a4179..678c647b778f 100644 >>>>>>> --- a/mm/util.c >>>>>>> +++ b/mm/util.c >>>>>>> @@ -667,6 +667,7 @@ void *__kvmalloc_node_noprof(DECL_BUCKET_PARAMS(size, b), gfp_t flags, int node) >>>>>>> >>>>>>> /* Don't even allow crazy sizes */ >>>>>>> if (unlikely(size > INT_MAX)) { >>>>>>> + BUG_ON(flags & __GFP_NOFAIL); >>>>>> >>>>>> No new BUG_ON please. WARN_ON_ONCE() + recovery code might be suitable here. >>>>> >>>>> Hi David, >>>>> WARN_ON_ONCE() might be fine but I don't see how it is possible to recover. >>>> >>>> Just return NULL? "shit in shit out" :) ? >>> >>> Returning NULL is perfectly right if gfp doesn't include __GFP_NOFAIL, >>> as it's the caller's responsibility to check the return value. However, with >>> __GFP_NOFAIL, users will directly dereference *(p + offset) even when >>> p == NULL. It is how __GFP_NOFAIL is supposed to work. >> >> If the caller is not supposed to pass that flag combination (shit in), >> we are not obligated to give a reasonable result (shit out). >> >> My point is that we should let the caller (possibly?) crash -- the one >> that did something that is wrong -- instead of forcing a crash using >> BUG_ON in this code here. >> >> It should all be caught during testing either way. And if some OOT >> module does something nasty, that's not our responsibility. >> >> BUG_ON is not a way to write assertions into the code. > > It seems there was a misunderstanding regarding the purpose of > this change. we actually have many details in changelog. > > Its aim is not to write an assertion, but rather to prevent exposing > a security vulnerability. > > Returning NULL doesn't necessarily crash the caller's process, p->field, > *(p + offset) deference could be used by hackers to exploit the system. See my other reply to Michal: why do we even allow to specify them separately and not simply let one enforce the other? That might result in an issue elsewhere, but likely no security vulnerability? I really hate each and every BUG_ON I have to stare at. -- Cheers, David / dhildenb