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Mon, 28 Jul 2025 17:39:08 +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 Ulj7Mry1h2jZTQAAD6G6ig (envelope-from ); Mon, 28 Jul 2025 17:39:08 +0000 Message-ID: <97938dc6-5dfe-4591-ba53-3729934c1235@suse.cz> Date: Mon, 28 Jul 2025 19:39:08 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] mm: fix a UAF when vma->mm is freed after vma->vm_refcnt got dropped Content-Language: en-US To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, jannh@google.com, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, pfalcato@suse.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20250728170950.2216966-1-surenb@google.com> <3f8c28f4-6935-4581-83ec-d3bc1e6c400e@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-Rspam-User: X-Rspamd-Queue-Id: 8C5BA40005 X-Rspamd-Server: rspam06 X-Stat-Signature: 7mhmbk4wt6rmydphs6em64obddp8frie X-HE-Tag: 1753724351-223635 X-HE-Meta: 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 3I5kshtk K7INXvAjN0iA1ILLtiZ1DNcpFkcqCT22/CGL4CTK8tp5+9QZ22CHkEi1SFMz0kgNqJOIkZcQ2YOqLT/3zMulXPre61ZOvQdCqvDkTaYfhO+i4co2A3jmsUFtGfnGB58iyroceYgQPiCfij/MLTiBa6oM8TQ65BcQNHz9Dul8kHhkXs2qX/uBPFdF09hiuHkAkBOlflHxqjqrN8mzOyKFXCc78iKwKTrWwrB28c/YJ8UagEb++fEbMpT+w0Se7mSWKiy48+6ILqECpfYOjhwd7lqtFLMP8NPZ6WtJfA0tVg88A80wd7dPmhjNCCxaKApfthT/3oxM5rcjrj4QSDNWIO3mtj2IwSJ3dPPcV 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 7/28/25 19:37, Suren Baghdasaryan wrote: > On Mon, Jul 28, 2025 at 10:19 AM Vlastimil Babka wrote: >> > + */ >> > + if (unlikely(vma->vm_mm != mm)) { >> > + /* >> > + * __mmdrop() is a heavy operation and we don't need RCU >> > + * protection here. Release RCU lock during these operations. >> > + */ >> > + rcu_read_unlock(); >> > + mmgrab(vma->vm_mm); >> > + vma_refcount_put(vma); >> >> The vma can go away here. > > No, the vma can't go away here because we are holding vm_refcnt. So, > the vma and its mm are stable up until vma_refcount_put() drops > vm_refcnt. But that's exactly what we're doing here? >> >> > + mmdrop(vma->vm_mm); And here we reference the vma again? >> So we need to copy the vma->vm_mm first? >> >> > + rcu_read_lock(); >> > + return NULL; >> > + } >> > + >> > /* >> > * Overflow of vm_lock_seq/mm_lock_seq might produce false locked result. >> > * False unlocked result is impossible because we modify and check