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Thu, 21 Nov 2024 06:18:21 -0800 (PST) MIME-Version: 1.0 References: <20241121124113.66166-1-aha310510@gmail.com> <26b82074-891f-4e26-b0a7-328ee2fa08d3@redhat.com> <25ead85f-2716-4362-8fb5-3422699e308c@redhat.com> In-Reply-To: <25ead85f-2716-4362-8fb5-3422699e308c@redhat.com> From: Jeongjun Park Date: Thu, 21 Nov 2024 23:18:12 +0900 Message-ID: Subject: Re: [PATCH] mm/huge_memory: Fix to make vma_adjust_trans_huge() use find_vma() correctly To: David Hildenbrand Cc: akpm@linux-foundation.org, dave@stgolabs.net, willy@infradead.org, Liam.Howlett@oracle.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Lorenzo Stoakes Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 0B38F1C000A X-Stat-Signature: omrfhty6s3qei4ag8ii355kroenbcpt7 X-HE-Tag: 1732198636-323297 X-HE-Meta: U2FsdGVkX1/1CAhSPy9Rlp7JUgV5+uTtPRemROP0Qh06nhPpHOkVYVOtNYPNabvloHg1vm7mnaUY5AuLIhl/P0kW3OCHIJkDsVoKGf4rlbIzQ6kXhFpF024fQ7IKQy77M49+wttkVGKkmJgkWs/8UNRXHosZzKInH3XZ04qmrgvtDy/TKbTzIrgLJ7MUyGTuzLxNUHQhuobQuV8FdlYnK5cKyugkn8Ajy9qPKiwijxvzlyPigIO90IXOIe6cuypHWpu7RpAaPwpFp96o/8C2DunJYSJlr7P7LXmMaU3RaQTxIIiTGK7vXio015pw8xQyFZFObQIY9E+s8Z7ncei6pt5cm9ofW8IoovGflXxZhEGFTx/5mB23vfvfi4nX3EV7Y4a6b1LxuCW+TxHroqNKjxY/LHEoMVZU3zaQtxob2XHnW3pQLoAYNIsj9iFOwSw3dDFa+09sd3u9/1xJjj5JLLO4p2WfsnoZX+kh5mY44Qj+bLW+QNtDgTsd3bqXx4aA+QSTE9rmIV6FcTGl02EanMn8l1/OvteYIyWPyiRxZgYYUhU/0A962ig45X9uU76neuRYf5knywyoYxU3RBm9ZZrD571B+mkP/Kv4wOLOzKdxHdx2mJOUPBkaLcoU2taWYPiEOQrcqrKXZqXo+7JIZsjkJSarpyqjXAfqsG2d6DNEpZyYoHddmwbYQ2GbxdVZ7QW9nMrt7ErVTBQZ7hRuQ3fA8OCFaCIZr0qTyCk+OajptN+nTjioUyzobplxsQcn2FrmjwWrWRoDF8Pec9y3TK4D7rpcg+/FiZ5I+UkC++C8m2F6AcNTwbn8IBdn1tsmpfwT8f7QboFX4OuLlXbFb034rf3G3svgkGBlfkHGxDCR/l/c+ntyPIVvyFt9C0PtAQxH2i+1ffc1jiXMWC5h+UTguMXB/6wlrK4JUXeW7nb3hhGZMKL+NJ8ni+oOVK2tlsHLaoNv2FjyzeR4UtY rATz6opJ 9hhRcoAlGaS1wYJkYDEMTf4VVSA1M/TDIPLhY0SfX9iUynsGZmrMCA5ZiLstWGHb3UUnN8BF43apB3jguOWyAqggO1SyFTm0MSeWUF6SDcfFP+TMS/xq+CMhtb6HrCWAAQTf8uTg3MQGx/YULiv9OMFE5VS403aSUhUnA+mC+i7YcDtzsjiomiO548/K66STyaixiZxakdJAvVjMx/NJ6FJVu9kj6OHiJYvWmTKHTmkNF1LzKB85Z+NNN7+/M9YrTn9e2NhmLRWeqBY/ldasiYeT+9IDGndzPTNFGSALU2DIO1jsczEGFcot0LGM7BIRPbQuda+7fAq5eT5D7ficN8qL8Rk9VBkVxa6mt6AZza0qsq4UZrKsxFuWnIIgANnfwclfMRnHy8hiBGYQgyxq+4gQZBg/v6sTqK4mA X-Bogosity: Ham, tests=bogofilter, spamicity=0.000176, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: David Hildenbrand wrote: > > On 21.11.24 14:44, David Hildenbrand wrote: > > On 21.11.24 13:41, Jeongjun Park wrote: > >> vma_adjust_trans_huge() uses find_vma() to get the VMA, but find_vma() uses > >> the returned pointer without any verification, even though it may return NULL. > >> In this case, NULL pointer dereference may occur, so to prevent this, > >> vma_adjust_trans_huge() should be fix to verify the return value of find_vma(). > >> > >> Cc: > >> Fixes: 685405020b9f ("mm/khugepaged: stop using vma linked list") > > > > If that's an issue, wouldn't it have predated that commit? > > > > struct vm_area_struct *next = vma->vm_next; > > unsigned long nstart = next->vm_start; > > > > Would have also assumed that there is a next VMA that can be > > dereferenced, no? > > > > And looking into the details, we only assume that there is a next VMA if > we are explicitly told to by the caller of vma_adjust_trans_huge() using > "adjust_next". > > There is only one such caller, > vma_merge_existing_range()->commit_merge() where we set adj_start -> > "adjust_next" where we seem to have a guarantee that there is a next VMA. I also thought that it would not be a problem in general cases, but I think that there may be a special case (for example, a race condition...?) that can occur in certain conditions, although I have not found it yet. In addition, most functions except this one unconditionally check the return value of find_vma(), so I think it would be better to handle the return value of find_vma() consistently in this function as well, rather than taking the risk and leaving it alone just because it seems to be okay. Regards, Jeongjun Park > > So I don't think there is an issue here (although the code does look > confusing ...). > > Not sure, though, if a > > if (WARN_ON_ONCE(!next)) > return; > > would be reasonable. > > -- > Cheers, > > David / dhildenb >