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Thu, 12 Oct 2023 10:04:37 -0700 (PDT) Received: from lucifer.home ([2a00:23c5:dc8c:8701:1663:9a35:5a7b:1d76]) by smtp.googlemail.com with ESMTPSA id h16-20020adffd50000000b003197869bcd7sm18875418wrs.13.2023.10.12.10.04.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 12 Oct 2023 10:04:36 -0700 (PDT) From: Lorenzo Stoakes To: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton Cc: Mike Kravetz , Muchun Song , Alexander Viro , Christian Brauner , Matthew Wilcox , Hugh Dickins , Andy Lutomirski , Jan Kara , linux-fsdevel@vger.kernel.org, bpf@vger.kernel.org, Lorenzo Stoakes Subject: [PATCH v4 3/3] mm: perform the mapping_map_writable() check after call_mmap() Date: Thu, 12 Oct 2023 18:04:30 +0100 Message-ID: <55e413d20678a1bb4c7cce889062bbb07b0df892.1697116581.git.lstoakes@gmail.com> X-Mailer: git-send-email 2.42.0 In-Reply-To: References: MIME-Version: 1.0 X-Rspamd-Queue-Id: C4CE32000E X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: zz3kucjxtabi9a8kj1hc1to58pc73ou1 X-HE-Tag: 1697130279-863664 X-HE-Meta: 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 gfcaAFIv COcT2uVLE/a0MD+N75bUuP1UGz7vsmFS/tI6J0wRqTazVu7P3xyzpkq3KzwUitABHVcRpB2m5+9zoAjpZL4zoyXdHRAeUGpCk/Y25HB7wPhIzrrRdwPjaRkr7M91dMIFZfP5ujKmX+TZfgDqoxZcRY8xcbEhswnKWJbN5+U7z1F+LRwBT3ppeaTapQCa1bCnNZ2abhTXquxVtGfi3GV5ukQX0RrYAW878BG2FpmDVl1Su/vAZoYyDiHpEeKzlZF46tXwHWseRY5GzCJ2kYVPY1k3rUqLNTeX5wA+iqtbriioRKUw+rBjCLg+QwXXx5on0qP2WLkVMYEzoAGp1rI7G7D4yrVtls78RhAWYckKtGESKHuOs9J9gjdLxre5g4FWgJOUoQnUaWTXYUr4Aj4P6bRCZvaifA2+VGIMdrGrU9lwKplLcEeTYHGr0ogjZn+tiT6wl 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: In order for a F_SEAL_WRITE sealed memfd mapping to have an opportunity to clear VM_MAYWRITE, we must be able to invoke the appropriate vm_ops->mmap() handler to do so. We would otherwise fail the mapping_map_writable() check before we had the opportunity to avoid it. This patch moves this check after the call_mmap() invocation. Only memfd actively denies write access causing a potential failure here (in memfd_add_seals()), so there should be no impact on non-memfd cases. This patch makes the userland-visible change that MAP_SHARED, PROT_READ mappings of an F_SEAL_WRITE sealed memfd mapping will now succeed. There is a delicate situation with cleanup paths assuming that a writable mapping must have occurred in circumstances where it may now not have. In order to ensure we do not accidentally mark a writable file unwritable by mistake, we explicitly track whether we have a writable mapping and unmap only if we do. Link: https://bugzilla.kernel.org/show_bug.cgi?id=217238 Signed-off-by: Lorenzo Stoakes Signed-off-by: Lorenzo Stoakes --- mm/mmap.c | 23 ++++++++++++++--------- 1 file changed, 14 insertions(+), 9 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index 0041e3631f6c..7f45a08e7973 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2752,6 +2752,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr, unsigned long charged = 0; unsigned long end = addr + len; unsigned long merge_start = addr, merge_end = end; + bool writable_file_mapping = false; pgoff_t vm_pgoff; int error; VMA_ITERATOR(vmi, mm, addr); @@ -2846,17 +2847,19 @@ unsigned long mmap_region(struct file *file, unsigned long addr, vma->vm_pgoff = pgoff; if (file) { - if (is_shared_maywrite(vm_flags)) { - error = mapping_map_writable(file->f_mapping); - if (error) - goto free_vma; - } - vma->vm_file = get_file(file); error = call_mmap(file, vma); if (error) goto unmap_and_free_vma; + if (vma_is_shared_maywrite(vma)) { + error = mapping_map_writable(file->f_mapping); + if (error) + goto close_and_free_vma; + + writable_file_mapping = true; + } + /* * Expansion is handled above, merging is handled below. * Drivers should not alter the address of the VMA. @@ -2920,8 +2923,10 @@ unsigned long mmap_region(struct file *file, unsigned long addr, mm->map_count++; if (vma->vm_file) { i_mmap_lock_write(vma->vm_file->f_mapping); - if (vma_is_shared_maywrite(vma)) + if (vma_is_shared_maywrite(vma)) { mapping_allow_writable(vma->vm_file->f_mapping); + writable_file_mapping = true; + } flush_dcache_mmap_lock(vma->vm_file->f_mapping); vma_interval_tree_insert(vma, &vma->vm_file->f_mapping->i_mmap); @@ -2937,7 +2942,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr, /* Once vma denies write, undo our temporary denial count */ unmap_writable: - if (file && is_shared_maywrite(vm_flags)) + if (writable_file_mapping) mapping_unmap_writable(file->f_mapping); file = vma->vm_file; ksm_add_vma(vma); @@ -2985,7 +2990,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr, unmap_region(mm, &vmi.mas, vma, prev, next, vma->vm_start, vma->vm_end, vma->vm_end, true); } - if (file && is_shared_maywrite(vm_flags)) + if (writable_file_mapping) mapping_unmap_writable(file->f_mapping); free_vma: vm_area_free(vma);