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Thu, 09 Jul 2026 19:10:31 -0700 (PDT) Received: from ikb-h07-29-noble.in.iijlab.net ([202.214.97.5]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-38c7d38e084sm1395987a91.14.2026.07.09.19.10.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 09 Jul 2026 19:10:31 -0700 (PDT) Received: by ikb-h07-29-noble.in.iijlab.net (Postfix, from userid 1010) id AF4BC1495CB2; Fri, 10 Jul 2026 11:10:29 +0900 (JST) 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, Hajime Tazaki Subject: [PATCH] mm: nommu: free unused resources when mremap shrinks the vma Date: Fri, 10 Jul 2026 11:10:28 +0900 Message-ID: <20260710021028.892645-1-thehajime@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit WIP: 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. Link: https://sashiko.dev/#/patchset/20260702012546.665383-1-thehajime@gmail.com Signed-off-by: Hajime Tazaki --- mm/nommu.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/mm/nommu.c b/mm/nommu.c index 852ec9bd0505..10794e3b6be9 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -1598,7 +1598,17 @@ static unsigned long do_mremap(unsigned long addr, return (unsigned long) -ENOMEM; /* all checks complete - do it */ - vma->vm_end = vma->vm_start + new_len; + if (new_len < old_len) { + /* shrink only happens addr + new_len and old_len are in different pages */ + VMA_ITERATOR(vmi, current->mm, addr); + /* vmi_shrink_vma() needs from/to pointers to be removed, + * (mainly used in munmap) so, specify them. + */ + vmi_shrink_vma(&vmi, vma, addr + new_len, addr + old_len); + } else { + /* when there are no shrink, update vma. */ + vma->vm_end = vma->vm_start + new_len; + } return vma->vm_start; } -- 2.43.0