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Thu, 24 Jul 2025 08:38:06 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id c3gTE+7wgWjURAAAD6G6ig (envelope-from ); Thu, 24 Jul 2025 08:38:06 +0000 Message-ID: <702ab3bb-db4c-49cb-bb77-4e864cae610e@suse.cz> Date: Thu, 24 Jul 2025 10:38:06 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [BUG] hard-to-hit mm_struct UAF due to insufficiently careful vma_refcount_put() wrt SLAB_TYPESAFE_BY_RCU Content-Language: en-US To: Suren Baghdasaryan , Jann Horn Cc: Andrew Morton , "Liam R. Howlett" , Lorenzo Stoakes , Pedro Falcato , Linux-MM , kernel list References: <16c97e30-19c9-41e8-b73b-c0b3c8eceff3@suse.cz> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJnyBr8BQka0IFQAAoJECJPp+fMgqZkqmMQ AIbGN95ptUMUvo6aAdhxaOCHXp1DfIBuIOK/zpx8ylY4pOwu3GRe4dQ8u4XS9gaZ96Gj4bC+ jwWcSmn+TjtKW3rH1dRKopvC07tSJIGGVyw7ieV/5cbFffA8NL0ILowzVg8w1ipnz1VTkWDr 2zcfslxJsJ6vhXw5/npcY0ldeC1E8f6UUoa4eyoskd70vO0wOAoGd02ZkJoox3F5ODM0kjHu Y97VLOa3GG66lh+ZEelVZEujHfKceCw9G3PMvEzyLFbXvSOigZQMdKzQ8D/OChwqig8wFBmV QCPS4yDdmZP3oeDHRjJ9jvMUKoYODiNKsl2F+xXwyRM2qoKRqFlhCn4usVd1+wmv9iLV8nPs 2Db1ZIa49fJet3Sk3PN4bV1rAPuWvtbuTBN39Q/6MgkLTYHb84HyFKw14Rqe5YorrBLbF3rl M51Dpf6Egu1yTJDHCTEwePWug4XI11FT8lK0LNnHNpbhTCYRjX73iWOnFraJNcURld1jL1nV r/LRD+/e2gNtSTPK0Qkon6HcOBZnxRoqtazTU6YQRmGlT0v+rukj/cn5sToYibWLn+RoV1CE Qj6tApOiHBkpEsCzHGu+iDQ1WT0Idtdynst738f/uCeCMkdRu4WMZjteQaqvARFwCy3P/jpK uvzMtves5HvZw33ZwOtMCgbpce00DaET4y/UzsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZ8gcVAUJFhTonwAKCRAiT6fnzIKmZLY8D/9uo3Ut9yi2YCuASWxr7QQZ lJCViArjymbxYB5NdOeC50/0gnhK4pgdHlE2MdwF6o34x7TPFGpjNFvycZqccSQPJ/gibwNA zx3q9vJT4Vw+YbiyS53iSBLXMweeVV1Jd9IjAoL+EqB0cbxoFXvnjkvP1foiiF5r73jCd4PR rD+GoX5BZ7AZmFYmuJYBm28STM2NA6LhT0X+2su16f/HtummENKcMwom0hNu3MBNPUOrujtW khQrWcJNAAsy4yMoJ2Lw51T/5X5Hc7jQ9da9fyqu+phqlVtn70qpPvgWy4HRhr25fCAEXZDp xG4RNmTm+pqorHOqhBkI7wA7P/nyPo7ZEc3L+ZkQ37u0nlOyrjbNUniPGxPxv1imVq8IyycG AN5FaFxtiELK22gvudghLJaDiRBhn8/AhXc642/Z/yIpizE2xG4KU4AXzb6C+o7LX/WmmsWP Ly6jamSg6tvrdo4/e87lUedEqCtrp2o1xpn5zongf6cQkaLZKQcBQnPmgHO5OG8+50u88D9I rywqgzTUhHFKKF6/9L/lYtrNcHU8Z6Y4Ju/MLUiNYkmtrGIMnkjKCiRqlRrZE/v5YFHbayRD dJKXobXTtCBYpLJM4ZYRpGZXne/FAtWNe4KbNJJqxMvrTOrnIatPj8NhBVI0RSJRsbilh6TE m6M14QORSWTLRg== In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Stat-Signature: sria16dns77zh9haoshzne389axdwqwj X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 52F9D80004 X-Rspam-User: X-HE-Tag: 1753346288-604967 X-HE-Meta: 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 p2CSOPxd aFpNKzE9E8BojS7fzVOxMh02N7MbCY/WDqa63TaVhw9zY6+c4f8Aeab6piuxdYJndEcGY0s8W98VVkvFUqc/qdUxMtnBpWFTnKzBdWiKWnQqViNNIPCWtk1E+GXigcSOg6KshYCqDv5NRi22E8lqTHXtgjl/uC2rTsUO0RGV+1N6EbHNGURmyx1+pumg1QSr10kYy4xyCSKV/UUlPrqX7cvMneO4sFuf/PZFniUmg07QmpF1eGb/8WDKJ2TXc1NSHi8wS3kzjaux8Rzzc1ViOm80T1MpaVv1OZVeCNEhQk3Do/5m06yCrQrJ8EgNHdzYK7Sgq5POf85gpxoU= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/24/25 04:30, Suren Baghdasaryan wrote: > So, I think vma_refcount_put() can mmgrab(vma->mm) before calling > __refcount_dec_and_test(), to stabilize that mm and then mmdrop() > after it calls rcuwait_wake_up(). What do you think about this > approach, folks? Yeah except it would be wasteful to do for all vma_refcount_put(). Should be enough to have this version (as Jann suggested) for inval_end_read: part of lock_vma_under_rcu. I think we need it also for the vma_refcount_put() done in vma_start_read() when we fail the seqcount check? I think in that case the same thing can be happening too, just with different race windows? Also as Jann suggested, maybe it's not great (or even safe) to perform __mmdrop() under rcu? And maybe some vma_start_read() users are even more restricted? Maybe then we'd need to make __mmdrop_delayed() not RT-only, and use that. >> >> Vlastimil is right that if A1 was able to successfully elevate vma's >> refcount then: >> 1. vma must be attached to some valid mm. This is true because if the >> vma is detached, vma_start_read() would not be able to elevate its >> refcount. Once vma_start_read() elevates the refcount, vma will not >> detach from under us because vma_mark_detached() will block until no >> readers are using the vma. >> 2. vma->mm can't be destroyed from under us because of that >> exit_mmap()->vma_mark_detached() which again will ensure no readers >> are holding a reference to the vmas of that mm. >> >> So, a special version of vma_refcount_put() that takes mm as a >> parameter and does mmgrab/mmdrop before using that mm might work. I'll >> do some more digging and maybe test this solution with your reproducer >> to see if that works as I would expect. >> Thanks, >> Suren.