Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755165AbbLIJmi (ORCPT ); Wed, 9 Dec 2015 04:42:38 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:45620 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754092AbbLIJmV (ORCPT ); Wed, 9 Dec 2015 04:42:21 -0500 From: Luis Henriques To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: David Howells , Al Viro , Kamal Mostafa , Luis Henriques Subject: [PATCH 3.16.y-ckt 126/126] FS-Cache: Handle a write to the page immediately beyond the EOF marker Date: Wed, 9 Dec 2015 09:38:16 +0000 Message-Id: <1449653896-5236-127-git-send-email-luis.henriques@canonical.com> In-Reply-To: <1449653896-5236-1-git-send-email-luis.henriques@canonical.com> References: <1449653896-5236-1-git-send-email-luis.henriques@canonical.com> X-Extended-Stable: 3.16 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5054 Lines: 163 3.16.7-ckt21 -stable review patch. If anyone has any objections, please let me know. ------------------ From: David Howells commit 102f4d900c9c8f5ed89ae4746d493fe3ebd7ba64 upstream. Handle a write being requested to the page immediately beyond the EOF marker on a cache object. Currently this gets an assertion failure in CacheFiles because the EOF marker is used there to encode information about a partial page at the EOF - which could lead to an unknown blank spot in the file if we extend the file over it. The problem is actually in fscache where we check the index of the page being written against store_limit. store_limit is set to the number of pages that we're allowed to store by fscache_set_store_limit() - which means it's one more than the index of the last page we're allowed to store. The problem is that we permit writing to a page with an index _equal_ to the store limit - when we should reject that case. Whilst we're at it, change the triggered assertion in CacheFiles to just return -ENOBUFS instead. The assertion failure looks something like this: CacheFiles: Assertion failed 1000 < 7b1 is false ------------[ cut here ]------------ kernel BUG at fs/cachefiles/rdwr.c:962! ... RIP: 0010:[] [] cachefiles_write_page+0x273/0x2d0 [cachefiles] Signed-off-by: David Howells Signed-off-by: Al Viro [ kamal: backport to 3.13-stable: no __kernel_write(); thanks Ben H. ] Signed-off-by: Kamal Mostafa Signed-off-by: Luis Henriques --- fs/cachefiles/rdwr.c | 79 +++++++++++++++++++++++++++------------------------- fs/fscache/page.c | 2 +- 2 files changed, 42 insertions(+), 39 deletions(-) diff --git a/fs/cachefiles/rdwr.c b/fs/cachefiles/rdwr.c index 4b1fb5ca65b8..88483abe08d3 100644 --- a/fs/cachefiles/rdwr.c +++ b/fs/cachefiles/rdwr.c @@ -912,6 +912,15 @@ int cachefiles_write_page(struct fscache_storage *op, struct page *page) cache = container_of(object->fscache.cache, struct cachefiles_cache, cache); + pos = (loff_t)page->index << PAGE_SHIFT; + + /* We mustn't write more data than we have, so we have to beware of a + * partial page at EOF. + */ + eof = object->fscache.store_limit_l; + if (pos >= eof) + goto error; + /* write the page to the backing filesystem and let it store it in its * own time */ path.mnt = cache->mnt; @@ -919,49 +928,43 @@ int cachefiles_write_page(struct fscache_storage *op, struct page *page) file = dentry_open(&path, O_RDWR | O_LARGEFILE, cache->cache_cred); if (IS_ERR(file)) { ret = PTR_ERR(file); - } else { - ret = -EIO; - if (file->f_op->write) { - pos = (loff_t) page->index << PAGE_SHIFT; - - /* we mustn't write more data than we have, so we have - * to beware of a partial page at EOF */ - eof = object->fscache.store_limit_l; - len = PAGE_SIZE; - if (eof & ~PAGE_MASK) { - ASSERTCMP(pos, <, eof); - if (eof - pos < PAGE_SIZE) { - _debug("cut short %llx to %llx", - pos, eof); - len = eof - pos; - ASSERTCMP(pos + len, ==, eof); - } - } + goto error_2; + } - data = kmap(page); - file_start_write(file); - old_fs = get_fs(); - set_fs(KERNEL_DS); - ret = file->f_op->write( - file, (const void __user *) data, len, &pos); - set_fs(old_fs); - kunmap(page); - file_end_write(file); - if (ret != len) - ret = -EIO; + len = PAGE_SIZE; + if (eof & ~PAGE_MASK) { + if (eof - pos < PAGE_SIZE) { + _debug("cut short %llx to %llx", + pos, eof); + len = eof - pos; + ASSERTCMP(pos + len, ==, eof); } - fput(file); } - if (ret < 0) { - if (ret == -EIO) - cachefiles_io_error_obj( - object, "Write page to backing file failed"); - ret = -ENOBUFS; - } + data = kmap(page); + file_start_write(file); + old_fs = get_fs(); + set_fs(KERNEL_DS); + ret = file->f_op->write( + file, (const void __user *) data, len, &pos); + set_fs(old_fs); + kunmap(page); + fput(file); + if (ret != len) + goto error_eio; + + _leave(" = 0"); + return 0; - _leave(" = %d", ret); - return ret; +error_eio: + ret = -EIO; +error_2: + if (ret == -EIO) + cachefiles_io_error_obj(object, + "Write page to backing file failed"); +error: + _leave(" = -ENOBUFS [%d]", ret); + return -ENOBUFS; } /* diff --git a/fs/fscache/page.c b/fs/fscache/page.c index ed70714503fa..e387cc646868 100644 --- a/fs/fscache/page.c +++ b/fs/fscache/page.c @@ -801,7 +801,7 @@ static void fscache_write_op(struct fscache_operation *_op) goto superseded; page = results[0]; _debug("gang %d [%lx]", n, page->index); - if (page->index > op->store_limit) { + if (page->index >= op->store_limit) { fscache_stat(&fscache_n_store_pages_over_limit); goto superseded; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/