From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4CCB91BDFB; Wed, 3 Jan 2024 17:07:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="nhECL/wD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 834F6C433C7; Wed, 3 Jan 2024 17:07:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1704301651; bh=F+hulm2papHFDBMbDn1cc1qBohpQDFZmuzUWQrl1pJI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nhECL/wDdZ+kytlhx1DxejJDT3Nd0tdMjFAtKupB+447kcYuXlczT88Qd5AklvvEk 6TX7mNgs1qh3elqqTuuOvsGqCAI0g6b/0t0AE6WS14Z2mY7hTjxk8t31DQ+s4hjusD Y0sOwwVSeN8WYb+2nkPs5aC+gltiFxz2mB65b9rE= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Baokun Li , Jan Kara , Andreas Dilger , Christoph Hellwig , Dave Chinner , "Matthew Wilcox (Oracle)" , "Ritesh Harjani (IBM)" , Theodore Tso , yangerkun , Yu Kuai , Zhang Yi , Andrew Morton Subject: [PATCH 5.15 86/95] mm/filemap: avoid buffered read/write race to read inconsistent data Date: Wed, 3 Jan 2024 17:55:34 +0100 Message-ID: <20240103164906.966616097@linuxfoundation.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240103164853.921194838@linuxfoundation.org> References: <20240103164853.921194838@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Baokun Li commit e2c27b803bb664748e090d99042ac128b3f88d92 upstream. The following concurrency may cause the data read to be inconsistent with the data on disk: cpu1 cpu2 ------------------------------|------------------------------ // Buffered write 2048 from 0 ext4_buffered_write_iter generic_perform_write copy_page_from_iter_atomic ext4_da_write_end ext4_da_do_write_end block_write_end __block_commit_write folio_mark_uptodate // Buffered read 4096 from 0 smp_wmb() ext4_file_read_iter set_bit(PG_uptodate, folio_flags) generic_file_read_iter i_size_write // 2048 filemap_read unlock_page(page) filemap_get_pages filemap_get_read_batch folio_test_uptodate(folio) ret = test_bit(PG_uptodate, folio_flags) if (ret) smp_rmb(); // Ensure that the data in page 0-2048 is up-to-date. // New buffered write 2048 from 2048 ext4_buffered_write_iter generic_perform_write copy_page_from_iter_atomic ext4_da_write_end ext4_da_do_write_end block_write_end __block_commit_write folio_mark_uptodate smp_wmb() set_bit(PG_uptodate, folio_flags) i_size_write // 4096 unlock_page(page) isize = i_size_read(inode) // 4096 // Read the latest isize 4096, but without smp_rmb(), there may be // Load-Load disorder resulting in the data in the 2048-4096 range // in the page is not up-to-date. copy_page_to_iter // copyout 4096 In the concurrency above, we read the updated i_size, but there is no read barrier to ensure that the data in the page is the same as the i_size at this point, so we may copy the unsynchronized page out. Hence adding the missing read memory barrier to fix this. This is a Load-Load reordering issue, which only occurs on some weak mem-ordering architectures (e.g. ARM64, ALPHA), but not on strong mem-ordering architectures (e.g. X86). And theoretically the problem doesn't only happen on ext4, filesystems that call filemap_read() but don't hold inode lock (e.g. btrfs, f2fs, ubifs ...) will have this problem, while filesystems with inode lock (e.g. xfs, nfs) won't have this problem. Link: https://lkml.kernel.org/r/20231213062324.739009-1-libaokun1@huawei.com Signed-off-by: Baokun Li Reviewed-by: Jan Kara Cc: Andreas Dilger Cc: Christoph Hellwig Cc: Dave Chinner Cc: Matthew Wilcox (Oracle) Cc: Ritesh Harjani (IBM) Cc: Theodore Ts'o Cc: yangerkun Cc: Yu Kuai Cc: Zhang Yi Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/filemap.c | 9 +++++++++ 1 file changed, 9 insertions(+) --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2649,6 +2649,15 @@ ssize_t filemap_read(struct kiocb *iocb, end_offset = min_t(loff_t, isize, iocb->ki_pos + iter->count); /* + * Pairs with a barrier in + * block_write_end()->mark_buffer_dirty() or other page + * dirtying routines like iomap_write_end() to ensure + * changes to page contents are visible before we see + * increased inode size. + */ + smp_rmb(); + + /* * Once we start copying data, we don't want to be touching any * cachelines that might be contended: */