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Wed, 23 Jul 2025 18:10:58 +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 w/PqGbIlgWgBcQAAD6G6ig (envelope-from ); Wed, 23 Jul 2025 18:10:58 +0000 Message-ID: Date: Wed, 23 Jul 2025 20:10:58 +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: Jann Horn Cc: Andrew Morton , "Liam R. Howlett" , Lorenzo Stoakes , Suren Baghdasaryan , 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: 8bit X-Stat-Signature: btoxe4gjkt7bxr4jb6gz6crwzw6cz9jq X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 0E7334000F X-Rspam-User: X-HE-Tag: 1753294259-756875 X-HE-Meta: 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 u5xEChEz NPDBlo346uPuWSoDniKIPe2JiM9IeSeUC1QfdQid3z3MfCPQWQGdZVHWoZSaI2bvC137NroATvnpb0GjSVafIvF76QVzr3WL1gFuY2Jzs1snXE9/5KZ9hWqXDGcXoXzm3rgMWH7AdNqcj4B9oLJKu2Me0s4V0QACgopwFQkoT1YflGIiCIdKUe4R5uaUSmK5aBW5rN4W+uBjZ+/GfP4kvZ2B7v2UaYuoCr5GO82jMuTksg2dNn9sLlSw/fYpxfTJcIG0gLX0QjCj7O1t3AfrSdbndt78D96tQ1Jguxeej/om1jkDTIpj8ptB74Rc8RSQghXv0JNoDlsPlQ+aRl/yOtKpB/a7RAiR5f0ne 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 7/23/25 19:49, Jann Horn wrote: > On Wed, Jul 23, 2025 at 7:32 PM Vlastimil Babka wrote: >> On 7/23/25 18:26, Jann Horn wrote: >> > There's a racy UAF in `vma_refcount_put()` when called on the >> > `lock_vma_under_rcu()` path because `SLAB_TYPESAFE_BY_RCU` is used >> > without sufficient protection against concurrent object reuse: >> >> Oof. >> >> > I'm not sure what the right fix is; I guess one approach would be to >> > have a special version of vma_refcount_put() for cases where the VMA >> > has been recycled by another MM that grabs an extra reference to the >> > MM? But then dropping a reference to the MM afterwards might be a bit >> > annoying and might require something like mmdrop_async()... >> >> Would we need mmdrop_async()? Isn't this the case for mmget_not_zero() and >> mmput_async()? > > Now I'm not sure anymore if either of those approaches would work, > because they rely on the task that's removing the VMA to wait until we > do __refcount_dec_and_test() before deleting the MM... but I don't > think we have any such guarantee... I think it would be waiting in exit_mmap->vma_mark_detached(), but then AFAIU you're right and we'd really need to work with mmgrab/mmdrop because at that point the mmget_not_zero() would already be failing...