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(bras-base-aurron9127w-grc-62-70-24-86-62.dsl.bell.ca. [70.24.86.62]) by smtp.gmail.com with ESMTPSA id u10-20020a05620a120a00b0074d4cf8f9fcsm661141qkj.107.2023.05.17.08.04.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 May 2023 08:04:11 -0700 (PDT) From: Peter Xu To: linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Lorenzo Stoakes , Andrew Morton , "Liam R . Howlett" , Mark Rutland , Andrea Arcangeli , Mike Rapoport , peterx@redhat.com, Alexander Viro , linux-stable Subject: [PATCH 1/2] mm/uffd: Fix vma operation where start addr cuts part of vma Date: Wed, 17 May 2023 11:04:07 -0400 Message-Id: <20230517150408.3411044-2-peterx@redhat.com> X-Mailer: git-send-email 2.39.1 In-Reply-To: <20230517150408.3411044-1-peterx@redhat.com> References: <20230517150408.3411044-1-peterx@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It seems vma merging with uffd paths is broken with either register/unregister, where right now we can feed wrong parameters to vma_merge() and it's found by recent patch which moved asserts upwards in vma_merge() by Lorenzo Stoakes: https://lore.kernel.org/all/ZFunF7DmMdK05MoF@FVFF77S0Q05N.cambridge.arm.com/ The problem is in the current code base we didn't fixup "prev" for the case where "start" address can be within the "prev" vma section. In that case we should have "prev" points to the current vma rather than the previous one when feeding to vma_merge(). This patch will eliminate the report and make sure vma_merge() calls will become legal again. One thing to mention is that the "Fixes: 29417d292bd0" below is there only to help explain where the warning can start to trigger, the real commit to fix should be 69dbe6daf104. Commit 29417d292bd0 helps us to identify the issue, but unfortunately we may want to keep it in Fixes too just to ease kernel backporters for easier tracking. Cc: Lorenzo Stoakes Cc: Mike Rapoport (IBM) Cc: Liam R. Howlett Reported-by: Mark Rutland Fixes: 29417d292bd0 ("mm/mmap/vma_merge: always check invariants") Fixes: 69dbe6daf104 ("userfaultfd: use maple tree iterator to iterate VMAs") Closes: https://lore.kernel.org/all/ZFunF7DmMdK05MoF@FVFF77S0Q05N.cambridge.arm.com/ Cc: linux-stable Signed-off-by: Peter Xu --- fs/userfaultfd.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 0fd96d6e39ce..17c8c345dac4 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -1459,6 +1459,8 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx, vma_iter_set(&vmi, start); prev = vma_prev(&vmi); + if (vma->vm_start < start) + prev = vma; ret = 0; for_each_vma_range(vmi, vma, end) { @@ -1625,6 +1627,9 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx, vma_iter_set(&vmi, start); prev = vma_prev(&vmi); + if (vma->vm_start < start) + prev = vma; + ret = 0; for_each_vma_range(vmi, vma, end) { cond_resched(); -- 2.39.1