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[34.127.76.238]) by smtp.gmail.com with ESMTPSA id l9-20020a170903120900b0016bfbd99f64sm11331143plh.118.2022.08.09.11.49.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Aug 2022 11:49:11 -0700 (PDT) Date: Tue, 9 Aug 2022 18:49:07 +0000 From: Carlos Llamas To: Liam Howlett Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , syzbot , Andrew Morton , Ondrej Mosnacek , "syzkaller-bugs@googlegroups.com" , Minchan Kim , Christian Brauner , Greg Kroah-Hartman , Hridya Valsaraju , Joel Fernandes , Martijn Coenen , Suren Baghdasaryan , Todd Kjos , Matthew Wilcox , Arve =?iso-8859-1?B?SGr4bm5lduVn?= Subject: Re: [PATCH] binder_alloc: Add missing mmap_lock calls when using the VMA Message-ID: References: <20220809160618.1052539-1-Liam.Howlett@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220809160618.1052539-1-Liam.Howlett@oracle.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 09, 2022 at 04:06:31PM +0000, Liam Howlett wrote: > Take the mmap_read_lock() when using the VMA in > binder_alloc_print_pages() and when checking for a VMA in > binder_alloc_new_buf_locked(). > > It is worth noting binder_alloc_new_buf_locked() drops the VMA read lock > after it verifies a VMA exists, but may be taken again deeper in the > call stack, if necessary. > > Reported-by: Ondrej Mosnacek > Reported-by: syzbot+a7b60a176ec13cafb793@syzkaller.appspotmail.com > Fixes: a43cfc87caaf (android: binder: stop saving a pointer to the VMA) > Signed-off-by: Liam R. Howlett > --- > drivers/android/binder_alloc.c | 29 +++++++++++++++++++---------- > 1 file changed, 19 insertions(+), 10 deletions(-) > > diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c > index f555eebceef6..c23cad7fe313 100644 > --- a/drivers/android/binder_alloc.c > +++ b/drivers/android/binder_alloc.c > @@ -395,12 +395,15 @@ static struct binder_buffer *binder_alloc_new_buf_locked( > size_t size, data_offsets_size; > int ret; > > + mmap_read_lock(alloc->vma_vm_mm); > if (!binder_alloc_get_vma(alloc)) { > + mmap_read_unlock(alloc->vma_vm_mm); > binder_alloc_debug(BINDER_DEBUG_USER_ERROR, > "%d: binder_alloc_buf, no vma\n", > alloc->pid); > return ERR_PTR(-ESRCH); > } > + mmap_read_unlock(alloc->vma_vm_mm); > > data_offsets_size = ALIGN(data_size, sizeof(void *)) + > ALIGN(offsets_size, sizeof(void *)); > @@ -922,17 +925,23 @@ void binder_alloc_print_pages(struct seq_file *m, > * Make sure the binder_alloc is fully initialized, otherwise we might > * read inconsistent state. > */ > - if (binder_alloc_get_vma(alloc) != NULL) { > - for (i = 0; i < alloc->buffer_size / PAGE_SIZE; i++) { > - page = &alloc->pages[i]; > - if (!page->page_ptr) > - free++; > - else if (list_empty(&page->lru)) > - active++; > - else > - lru++; > - } > + > + mmap_read_lock(alloc->vma_vm_mm); > + if (binder_alloc_get_vma(alloc) == NULL) > + goto uninitialized; > + > + for (i = 0; i < alloc->buffer_size / PAGE_SIZE; i++) { do we need to hold on to the lock while we loop through the pages here? > + page = &alloc->pages[i]; > + if (!page->page_ptr) > + free++; > + else if (list_empty(&page->lru)) > + active++; > + else > + lru++; > } > + > +uninitialized: > + mmap_read_unlock(alloc->vma_vm_mm); > mutex_unlock(&alloc->mutex); > seq_printf(m, " pages: %d:%d:%d\n", active, lru, free); > seq_printf(m, " pages high watermark: %zu\n", alloc->pages_high); > -- > 2.35.1