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Fri, 9 Jan 2026 18:04:21 +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 OH/4LyVDYWkRAgAAD6G6ig (envelope-from ); Fri, 09 Jan 2026 18:04:21 +0000 Message-ID: <4de2c1e7-73f3-4aa9-81ac-4de39f60c95e@suse.cz> Date: Fri, 9 Jan 2026 19:04:21 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/4] mm/vma: fix anon_vma UAF on mremap() faulted, unfaulted merge Content-Language: en-US To: Lorenzo Stoakes , Andrew Morton Cc: "Liam R . Howlett" , Jann Horn , Pedro Falcato , Yeoreum Yun , linux-mm@kvack.org, linux-kernel@vger.kernel.org, David Hildenbrand , Jeongjun Park , Rik van Riel , Harry Yoo References: 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-Stat-Signature: o9jaz4os1pkfjtxm6hmmncinncxe6xoi X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 7D71E20011 X-Rspam-User: X-HE-Tag: 1767981865-411569 X-HE-Meta: U2FsdGVkX18Imx1AYeDjGz16rmNtBbIk9ymeJ6nlRmFEuEiudEuX/jJdFJQcJV9tjHlm+w3E13C/eva+Y2nn3RHPDRLvLjlU0yPPlzKuaPY6aTNSdL4bh4WtpxHnkkDMIJs0eFzPo4FvLk1iQ6G+Dpl119G/PzJS17jkIUz9wf6FSR/zNAC+ygrbQBIg7q8vznGTr4U8XQTHNnY2f5pD13RFuG6UAFvpJ3G/JtSbIAxp3cqwZdU6YSsiAhrhmt9rfSyk78gD3lmaGFQIvOkGRh69/QK5+l17cSrRE98H5oNOWAnp/K47HwdsJEDAfzmtihxbMcEaySEENHMLH85VZfVtYoxq/xDdkz74mj4gH0vrT3lGwhC11+L/sFeldaqLTSOvNDQ17tAhghfD/VbbXzq10do7dYMR2ghUeRZ0RwAskTYsCmzYc3hSdDVz8Tn3c2OE16NskJRhXqMQn1UJif3uR2HGx40lCyeJgrWUPfXdwr94WRECAKLdWQp3a3BOheDWCr8ekVTc7cGU3FOJwjIdGlf0ZmRjMGpBhZs2oCLYWFPIZhfusk9GHCelfhvIPX5+ucDtTqDkhS/FM+0szk0Spz2J92JtLRejZqeCrN8ix82Tk/sJWhmV7i6mLeu7tWUz49klsBL0hVt0V9p3nqRJWkxkO2q71MtB5AXybXRo45ncU8ys4FwBX/Ki1pF8mz2/RcEpfvv4pQBlnkqAJP/gSu6be7vsX0lOp7+49S1/NSHyZdSPFVQi2TbOqbUD9YBNi9AZmzcGVTnwl3h7MuMsuUr0xnxHi2dGhuGn67K5ZXGSYYjJcK45/txpup1Yx6AD2gWYCzze5LokVOCN3TpDdTfcYiKknJIOZCrmVFeNyoSFzt5yrRSBM8r1aEUgX2Nb7htOYC6JxGOc6nu9llI8kOwDeRNT7YK5lE6jQvPJHRIamTVOVGH/WWuYbmr+Xpot2TMdwpVlBwCrLVB hOwfL692 Wl938wOneSkIXZvBOLA2/Sq72TU5T7uSwoLyd7sbxATr+Ie6ysM/8skPlWi681pmp8qlSbviDcyH1zRaBN+gqxPJXies2hQ+44q6VGGDrapd9YREJdWyPehjIe/11KbEJu518qtHci7wsgnGlE649o4VtQIGOrcOap+bikTyc8I0ztY4liv3951fjzOZMLs4xj8ZNmbIRkiU0RDUhcMsCg+Q7oJHkzs8UqJ+x14CLQmRoxErbjDKk7P7ZzVSnukk05YLJMz3dYs/L8CCE2hCr6bPiQ7LNbfxGhINfU8r+niWQWzxr0G8jzl51qEEBpJ/UwHUddmAOPq1tBtkKnUBn17p9YxTQTJ2M5NZ6a4FszElnluExXI7usHQM7Pnvyrf8927XmeTbzTzVt0nE1h694NiBC7tfOiI0lrAKg/jFV7038BqibrzNAtvmOOpX3JHNGrC8YonIz0eaCygVUbGw8euVeA== 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 1/5/26 21:11, Lorenzo Stoakes wrote: > This bug was discovered via a syzbot report, which this patch resolves. > > We further make a change to update the mergeable anon_vma check to assert > the copied-from anon_vma did not have CoW parents, as otherwise > dup_anon_vma() might incorrectly propagate CoW ancestors from the next VMA > in case 4 despite the anon_vma's being identical for both VMAs. > > Signed-off-by: Lorenzo Stoakes > Fixes: 879bca0a2c4f ("mm/vma: fix incorrectly disallowed anonymous VMA merges") > Reported-by: syzbot+b165fc2e11771c66d8ba@syzkaller.appspotmail.com > Closes: https://lore.kernel.org/all/694a2745.050a0220.19928e.0017.GAE@google.com/ > Cc: stable@kernel.org Acked-by: Vlastimil Babka Nit below: > @@ -1117,46 +1146,52 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg) > int vma_expand(struct vma_merge_struct *vmg) > { > struct vm_area_struct *anon_dup = NULL; > - bool remove_next = false; > struct vm_area_struct *target = vmg->target; > struct vm_area_struct *next = vmg->next; > + bool remove_next = false; > vm_flags_t sticky_flags; > - > - sticky_flags = vmg->vm_flags & VM_STICKY; > - sticky_flags |= target->vm_flags & VM_STICKY; > - > - VM_WARN_ON_VMG(!target, vmg); > + int ret = 0; > > mmap_assert_write_locked(vmg->mm); > - > vma_start_write(target); > - if (next && (target != next) && (vmg->end == next->vm_end)) { > - int ret; > > - sticky_flags |= next->vm_flags & VM_STICKY; > + if (next && target != next && vmg->end == next->vm_end) > remove_next = true; > - /* This should already have been checked by this point. */ > - VM_WARN_ON_VMG(!can_merge_remove_vma(next), vmg); > - vma_start_write(next); > - /* > - * In this case we don't report OOM, so vmg->give_up_on_mm is > - * safe. > - */ > - ret = dup_anon_vma(target, next, &anon_dup); > - if (ret) > - return ret; > - } > > + /* We must have a target. */ > + VM_WARN_ON_VMG(!target, vmg); > + /* This should have already been checked by this point. */ > + VM_WARN_ON_VMG(remove_next && !can_merge_remove_vma(next), vmg); > /* Not merging but overwriting any part of next is not handled. */ > VM_WARN_ON_VMG(next && !remove_next && > next != target && vmg->end > next->vm_start, vmg); > - /* Only handles expanding */ > + /* Only handles expanding. */ > VM_WARN_ON_VMG(target->vm_start < vmg->start || > target->vm_end > vmg->end, vmg); > > + sticky_flags = vmg->vm_flags & VM_STICKY; > + sticky_flags |= target->vm_flags & VM_STICKY; > if (remove_next) > - vmg->__remove_next = true; > + sticky_flags |= next->vm_flags & VM_STICKY; > > + /* > + * If we are removing the next VMA or copying from a VMA > + * (e.g. mremap()'ing), we must propagate anon_vma state. > + * > + * Note that, by convention, callers ignore OOM for this case, so > + * we don't need to account for vmg->give_up_on_mm here. It's called "give_up_on_oom". It was already wrong so this comment move would be a chance to fix it. I think Andrew can just edit locally? > + */ > + if (remove_next) > + ret = dup_anon_vma(target, next, &anon_dup); > + if (!ret && vmg->copied_from) > + ret = dup_anon_vma(target, vmg->copied_from, &anon_dup); > + if (ret) > + return ret; > + > + if (remove_next) { > + vma_start_write(next); > + vmg->__remove_next = true; > + } > if (commit_merge(vmg)) > goto nomem; > > @@ -1828,10 +1863,9 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, > if (new_vma && new_vma->vm_start < addr + len) > return NULL; /* should never get here */ > > - vmg.middle = NULL; /* New VMA range. */ > vmg.pgoff = pgoff; > vmg.next = vma_iter_next_rewind(&vmi, NULL); > - new_vma = vma_merge_new_range(&vmg); > + new_vma = vma_merge_copied_range(&vmg); > > if (new_vma) { > /* > diff --git a/mm/vma.h b/mm/vma.h > index e4c7bd79de5f..d51efd9da113 100644 > --- a/mm/vma.h > +++ b/mm/vma.h > @@ -106,6 +106,9 @@ struct vma_merge_struct { > struct anon_vma_name *anon_name; > enum vma_merge_state state; > > + /* If copied from (i.e. mremap()'d) the VMA from which we are copying. */ > + struct vm_area_struct *copied_from; > + > /* Flags which callers can use to modify merge behaviour: */ > > /*