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[221.241.217.81]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-847f6d7a98asm9738725b3a.42.2026.07.10.00.30.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 10 Jul 2026 00:30:11 -0700 (PDT) Date: Fri, 10 Jul 2026 16:30:08 +0900 Message-ID: From: Hajime Tazaki To: akpm@linux-foundation.org, liam@infradead.org, ljs@kernel.org, vbabka@kernel.org, jannh@google.com, pfalcato@suse.de, linux-mm@kvack.org, geert@linux-m68k.org Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm: nommu: free unused resources when mremap shrinks the vma In-Reply-To: <20260710054648.924005-1-thehajime@gmail.com> References: <20260710054648.924005-1-thehajime@gmail.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/27.2 Mule/6.0 MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: 9D87E100010 X-Rspam-User: X-Stat-Signature: 8k75mant5z68xf843pcscfptrewcoj5p X-Rspamd-Server: rspam03 X-HE-Tag: 1783668614-555534 X-HE-Meta: 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 839n4MUW KtA29dDF/psXu7QTKP7018R3fF6dCl5uCbctr3OX2x+zRJW6Gp8AYo7Dzy3+3ZYHJUjUJWIRA6qgfMUgbujJPdH0wSOwqwoUrfZzKpUedVo16b3Jhhsy2ZkO4xa/swzHaJ/KJEE4woWvwLTGeLjX7C0Fplxvg5ZAbCrzwUUxb5vTOmxM448gGpzYZiyo+SYe5IMVpneos+MUQe255O4pM1yNBiZ1hM6yEOVI99wsD2Jt51PP1civak3Ss75mdiZXjY/MGp3Z7phJFlvXyzBLrC46qf49gxC51wIDDT8WWmsx9+KBm5GhXh3BOYUXaVCTMgjv3WfTeiUFhRfRFlUsJ+GfeMXc6muDzXpt4Y2DgpemIUFd9sD212hmuF4u6VgPxDsA39L/j3166Oo7zJoSUZ3p2Aw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 10 Jul 2026 14:46:48 +0900, Hajime Tazaki wrote: > > When shrinking a VMA via mremap, the bounds are modified directly: > mm/nommu.c:do_mremap() { > ... > vma->vm_end = vma->vm_start + new_len; > ... > } > This shrink the VMA without updating its bounds in the maple tree. > If the maple tree (mm->mm_mt) still contains the old bounds, a user > process could access the freed portion. The stale maple tree would > incorrectly return the shrunk VMA for an address past its new vm_end. > > This commit fixes this issue by calling vmi_shrink_vma() when shrink > happens. Additionally, if a file-backed map is to be shrunk, it reports > -EINVAL like do_munmap() does. > > The issue is reported by Sashiko review, linked below. > > Link: https://sashiko.dev/#/patchset/20260702012546.665383-1-thehajime@gmail.com > Link: https://sashiko.dev/#/patchset/20260710021028.892645-1-thehajime%40gmail.com > Signed-off-by: Hajime Tazaki I think the original issue reported by Sashiko is addressed, but found another existing issue, which might take a bit to look into detail (e.g., currently under nommu we cannot map (actually kernel_read()) /dev/zero, vma_set_anonymous() isn't called for /dev/zero on nommu, etc). So I will address this in a different patch, not in this one. -- Hajime