From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752281AbcAFSBR (ORCPT ); Wed, 6 Jan 2016 13:01:17 -0500 Received: from mga02.intel.com ([134.134.136.20]:47400 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751981AbcAFSBM (ORCPT ); Wed, 6 Jan 2016 13:01:12 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.20,530,1444719600"; d="scan'208";a="885040062" From: Ross Zwisler To: linux-kernel@vger.kernel.org Cc: Ross Zwisler , "H. Peter Anvin" , "J. Bruce Fields" , "Theodore Ts'o" , Alexander Viro , Andreas Dilger , Andrew Morton , Dan Williams , Dave Chinner , Dave Hansen , Ingo Molnar , Jan Kara , Jeff Layton , Matthew Wilcox , Matthew Wilcox , Thomas Gleixner , linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-nvdimm@ml01.01.org, x86@kernel.org, xfs@oss.sgi.com Subject: [PATCH v7 1/9] dax: fix NULL pointer dereference in __dax_dbg() Date: Wed, 6 Jan 2016 11:00:55 -0700 Message-Id: <1452103263-1592-2-git-send-email-ross.zwisler@linux.intel.com> X-Mailer: git-send-email 2.5.0 In-Reply-To: <1452103263-1592-1-git-send-email-ross.zwisler@linux.intel.com> References: <1452103263-1592-1-git-send-email-ross.zwisler@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org __dax_dbg() currently assumes that bh->b_bdev is non-NULL, passing it into bdevname() where is is dereferenced. This assumption isn't always true - when called for reads of holes, ext4_dax_mmap_get_block() returns a buffer head where bh->b_bdev is never set. I hit this BUG while testing the DAX PMD fault path. Instead, verify that we have a valid bh->b_bdev, else just say "unknown" for the block device. Signed-off-by: Ross Zwisler Cc: Dan Williams --- fs/dax.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/fs/dax.c b/fs/dax.c index 7af8797..03cc4a3 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -563,7 +563,12 @@ static void __dax_dbg(struct buffer_head *bh, unsigned long address, { if (bh) { char bname[BDEVNAME_SIZE]; - bdevname(bh->b_bdev, bname); + + if (bh->b_bdev) + bdevname(bh->b_bdev, bname); + else + snprintf(bname, BDEVNAME_SIZE, "unknown"); + pr_debug("%s: %s addr: %lx dev %s state %lx start %lld " "length %zd fallback: %s\n", fn, current->comm, address, bname, bh->b_state, (u64)bh->b_blocknr, -- 2.5.0