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Thu, 24 Jul 2025 14:45:14 +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 grASF/pGgmgEOAAAD6G6ig (envelope-from ); Thu, 24 Jul 2025 14:45:14 +0000 Message-ID: <3be82198-a992-4917-b5ac-b93bb0474ad1@suse.cz> Date: Thu, 24 Jul 2025 16:45:14 +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 , Lorenzo Stoakes Cc: Jann Horn , Andrew Morton , "Liam R. Howlett" , Pedro Falcato , Linux-MM , kernel list References: <16c97e30-19c9-41e8-b73b-c0b3c8eceff3@suse.cz> <702ab3bb-db4c-49cb-bb77-4e864cae610e@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-Rspamd-Action: no action X-Stat-Signature: 1tbczsc11k8paxc54n9x9iaq3k1rfye1 X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 2975EC000F X-Rspam-User: X-HE-Tag: 1753368315-473549 X-HE-Meta: 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 CYAQtd19 DrHRFocLSY4AuZIn5OeArBwAGufIgecRjMdk0Kx5ZBDNgF9K4F6Qd2lBEzrtQIRjrnbWlDrTGB46O2tDUA9vD9cF67uWk0EYbJx/9DsKtIuY6rltcwrjJrd0qbUdE8aTFZE3/J2y1+ldoOjRIZwKTFb893gjVH+qR9rmD+SBPw3dOOzrzHUofozabQlA6VYTuFW22Tl3YJKUliddVBd1vnbeI0COeohU0xVMOOFR8SJY8sSc3WWWq3wwJhk6YD78jbhFUOCBdXMjCigpc4CuAW4AZy+3msR4SNvAtGbgbbE8lYIFUdfTrdRgcI1dcQDDu1meuw7p4XzypmjGY1JDzMomraJ/g8EdHBLOsYjrJbFqPfY0axy4l2jOUxHhA1+fO1VWl 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 16:29, Suren Baghdasaryan wrote: > On Thu, Jul 24, 2025 at 3:53 AM Lorenzo Stoakes > wrote: >> >> On Thu, Jul 24, 2025 at 10:38:06AM +0200, Vlastimil Babka wrote: >> > 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. > > Yes, definitely. > >> > 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? > > Yes. > >> > >> > 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. >> >> Agreed that doing this under RCU seems unwise. >> >> I know PTL relies on this as well as zap PTE page table reclaim, likely these >> wouldn't interact with an mm going away (you'd hope!) but it seems unwise to >> play around with assumptions here. > > __mmdrop_delayed() is a viable option but I would hate adding > mm->delayed_drop for !CONFIG_PREEMPT_RT just for this one case. > Alternatively, we don't need to be in the rcu read section when we > call vma_end_read() inside lock_vma_under_rcu(). We refcounted the > vma, so it's locked and stable, no need for RCU at that point. We can > move rcu_read_unlock() before vma_end_read(). However that's not the Seems correct. > case with the vma_refcount_put() inside vma_start_read(). We could > change vma_start_read() semantics so that it drops rcu_read_lock > before it returns. Looks like there's no other users of vma_start_read() than lock_vma_under_rcu() itself that we need to care about, so seems fine. > That way we could do vma_refcount_put() after > rcu_read_unlock() in both places. The retry case in > lock_vma_under_rcu() would have to reacquire rcu_read_lock() but that > retry is not the usual path, so should not affect overall locking > performance. What do you think about this alternative? Sounds feasible. I guess at that point it would be cleaner to combine vma_start_read() with mas_walk() into a new function that does both and starts with rcu_read_lock() itself so we don't have the ugly scheme of entering under rcu lock and returning without it?