From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793213473; b=yVmSodazK2pYu/fQnL844cbQz9KGZ+Ay9Y6QbmT+UoPL7dqidZnWbf7kon/yNPvo2JUM ZNHy7zjZADojYHjZN3e0IC7Yc8m227qq8ozudCqLNILUQGPUXIYeifm/LPhTGhXdp0J0d 2zFva5OGWJLvcINN7DjKbR0pK/N03J7rkmxuA1nr2+ZOZMzzL5+zJaFMtqKNfD7poyULr dWfqSQhiyAqNgx9WP19Hdx9hypfgQY65I/k4TsXbiUC7nGrmUkMvsQyNQmGRQPszy4l0C nsDbXQrTV+iOgaCJqiC7FjB1PEmNBKttM+jLW3wkAf3WT1yWVBjwRh9POoiD00bYGVw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793213473; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=A7rE/TNfAypJtMC1OuujUdC461Obv8C3BA77Rr71ikw=; b=ujC6NPhliaZAi8so76M3lN0XOBmZD+yFL3pxT/IQ0iggHU7HvIkoqclr8PLPxyifhUat 6sAJTM3DwH8UV0nMPYN6gw8BuDONrndAyeU09T0lLgcSWY6WyWD6q/dapiG7VElG9Mnfk efJOoyan6nZ4oxsn4qoRNTMqHPzZJBqF6yHPL80CRsGMxAoFBQKGwOWTusKu+V0LbeS0i L3Gd4Oxu84L4/XP37/wQMhdb1UYM0WlP/7c5VI2FHY/r36BWuG3EIV5WRPO7fV64+Q8JN qFS9En0MGAf6A4k3yLpi3mfqF1rtooqhUSC6ljMKd2gd1mFy8Do6DdPF3fG2wl8sdvA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=j78l++C4; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 13A86606A31A; Wed, 28 Oct 2026 18:51:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=j78l++C4 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 677961F01828; Wed, 28 Oct 2026 18:51:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793213472; bh=A7rE/TNfAypJtMC1OuujUdC461Obv8C3BA77Rr71ikw=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=j78l++C4k44kCBAwoPcn7VMA1ujMO51Q+fkQoab6xWXaqVvOIvKPOn4fH1yRCKxNI oR0Tx2uVPonEYIfHbDC5IfCojFkGmcwIey661Lf3RWlomTxNBrBmbb7AgxaKxRHRgl qm14SXZ5o2ksffx41jo585ZWbSI6u0vQHBE+ARHk= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Lorenzo Stoakes (ARM)" , Andrew Morton , Pedro Falcato , "Kiryl Shutsemau (Meta)" , "Jose A. Perez de Azpillaga" , Anirudh Srinivasan , Sasha Levin Subject: [PATCH 6.1 0517/1887] mm/mremap: fix locked_vm leak from MREMAP_DONTUNMAP self-merge Date: Wed, 28 Oct 2026 17:43:33 +0100 Message-ID: <20261028170511.086529899@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261028170459.200466217@linuxfoundation.org> References: <20261028170459.200466217@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Lorenzo Stoakes (ARM) [ Upstream commit 838bb60dc21553e32df90f2f3bac5b905376e7aa ] The MREMAP_DONTUNMAP feature is highly unusual in that it permits mremap() operations that keep the original VMA in place. Historically this has led to a lot of bugs where non-obvious interactions occur between existing mremap() operations and the original VMA. Fix another of these - self-merge. Self-merge occurs when a VMA is moved in front of or behind itself and the attributes of the VMA permit such a merge. Practically this can only happen for unfaulted anonymous VMAs due to the page offset equality requirement for merge: |------------| | | | v |...........||-----------||...........| | || unfaulted || | |...........||-----------||...........| ^ | | | |------------| This becomes problematic if the VMA is configured by the user to mlock-on-fault, i.e. the VMA_LOCKED_BIT, VMA_LOCKONFAULT_BIT VMA flags are set. MREMAP_DONTUNMAP clears mlock flags for the source VMA and maintains them for the destination VMA. Self-merge makes this impossible (there is only one VMA) and incorrectly clears the destination VMA's mlock flags. This causes a leak in mm->locked_vm as clearing this flag does not decrement the counter and the VMA no longer has VMA_LOCKED_BIT set so it is not decremented on unmap. Resolve this by simply disallowing a self-merge in this case - the source and destination VMAs are kept distinct and then are able to have distinct mlock() flags. Update to make the now-redundant self-merge check a VM_WARN_ON_ONCE() instead to guard against future regressions. Fixes: e346b3813067 ("mm/mremap: add MREMAP_DONTUNMAP to mremap()") Signed-off-by: Lorenzo Stoakes (ARM) Signed-off-by: Andrew Morton Reviewed-by: Pedro Falcato Acked-by: Kiryl Shutsemau (Meta) Reviewed-by: Jose A. Perez de Azpillaga Tested-by: Anirudh Srinivasan Cc: [ ljs - Converted to work with vma_merge(), tweaked commit msg. ] Signed-off-by: Lorenzo Stoakes (ARM) Signed-off-by: Sasha Levin --- include/linux/mm.h | 2 +- mm/mmap.c | 23 +++++++++++++++++++---- mm/mremap.c | 7 +++++-- 3 files changed, 25 insertions(+), 7 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 4f0aa81257c58..279c121ef6b3c 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2822,7 +2822,7 @@ extern int insert_vm_struct(struct mm_struct *, struct vm_area_struct *); extern void unlink_file_vma(struct vm_area_struct *); extern struct vm_area_struct *copy_vma(struct vm_area_struct **, unsigned long addr, unsigned long len, pgoff_t pgoff, - bool *need_rmap_locks); + bool *need_rmap_locks, bool keep_source); extern void exit_mmap(struct mm_struct *); void vma_mas_store(struct vm_area_struct *vma, struct ma_state *mas); diff --git a/mm/mmap.c b/mm/mmap.c index d39e31f15e86c..54c73823fba33 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -3337,13 +3337,14 @@ int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma) */ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, unsigned long addr, unsigned long len, pgoff_t pgoff, - bool *need_rmap_locks) + bool *need_rmap_locks, bool keep_source) { struct vm_area_struct *vma = *vmap; unsigned long vma_start = vma->vm_start; struct mm_struct *mm = vma->vm_mm; struct vm_area_struct *new_vma, *prev; bool faulted_in_anon_vma = true; + bool can_self_merge = false; validate_mm_mt(mm); /* @@ -3353,15 +3354,29 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, if (unlikely(vma_is_anonymous(vma) && !vma->anon_vma)) { pgoff = addr >> PAGE_SHIFT; faulted_in_anon_vma = false; + can_self_merge = true; } new_vma = find_vma_prev(mm, addr, &prev); if (new_vma && new_vma->vm_start < addr + len) return NULL; /* should never get here */ - new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags, - vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma), - vma->vm_userfaultfd_ctx, anon_vma_name(vma)); + /* + * If the original VMA is kept (MREMAP_DONTUNMAP), the source and + * destination VMA must be treated distinctly. + * + * A merge violates this, so in this case disallow a self-merge. A + * self-merge can only occur if the new range is immediately adjacent to + * the source VMA, so simply do not attempt to merge in that case. + */ + if (can_self_merge && keep_source && + (addr == vma->vm_end || vma->vm_start == addr + len)) + new_vma = NULL; + else + new_vma = vma_merge(mm, prev, addr, addr + len, vma->vm_flags, + vma->anon_vma, vma->vm_file, pgoff, + vma_policy(vma), vma->vm_userfaultfd_ctx, + anon_vma_name(vma)); if (new_vma) { /* * Source vma may have been merged into new_vma diff --git a/mm/mremap.c b/mm/mremap.c index e1d7047f6ee5e..5eca7534e8706 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -639,7 +639,7 @@ static unsigned long move_vma(struct vm_area_struct *vma, new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT); new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff, - &need_rmap_locks); + &need_rmap_locks, flags & MREMAP_DONTUNMAP); if (!new_vma) { if (vm_flags & VM_ACCOUNT) vm_unacct_memory(to_account >> PAGE_SHIFT); @@ -700,6 +700,9 @@ static unsigned long move_vma(struct vm_area_struct *vma, untrack_pfn_clear(vma); if (unlikely(!err && (flags & MREMAP_DONTUNMAP))) { + /* Self-merge is disallowed. */ + VM_WARN_ON_ONCE(new_vma == vma); + /* We always clear VM_LOCKED[ONFAULT] on the old vma */ vma->vm_flags &= VM_LOCKED_CLEAR_MASK; @@ -707,7 +710,7 @@ static unsigned long move_vma(struct vm_area_struct *vma, * anon_vma links of the old vma is no longer needed after its page * table has been moved. */ - if (new_vma != vma && vma->vm_start == old_addr && + if (vma->vm_start == old_addr && vma->vm_end == (old_addr + old_len)) { const pgoff_t pgoff_unfaulted = vma->vm_start >> PAGE_SHIFT; -- 2.53.0