From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f173.google.com (mail-qk0-f173.google.com [209.85.220.173]) by kanga.kvack.org (Postfix) with ESMTP id E2FF56B0005 for ; Wed, 6 Jan 2016 14:14:10 -0500 (EST) Received: by mail-qk0-f173.google.com with SMTP id p186so77838684qke.0 for ; Wed, 06 Jan 2016 11:14:10 -0800 (PST) Received: from mail-qk0-x22d.google.com (mail-qk0-x22d.google.com. [2607:f8b0:400d:c09::22d]) by mx.google.com with ESMTPS id j203si1851974qhc.107.2016.01.06.11.14.10 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 06 Jan 2016 11:14:10 -0800 (PST) Received: by mail-qk0-x22d.google.com with SMTP id h11so16963803qke.1 for ; Wed, 06 Jan 2016 11:14:10 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <1452103263-1592-2-git-send-email-ross.zwisler@linux.intel.com> References: <1452103263-1592-1-git-send-email-ross.zwisler@linux.intel.com> <1452103263-1592-2-git-send-email-ross.zwisler@linux.intel.com> Date: Wed, 6 Jan 2016 11:14:09 -0800 Message-ID: Subject: Re: [PATCH v7 1/9] dax: fix NULL pointer dereference in __dax_dbg() From: Dan Williams Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Ross Zwisler Cc: "linux-kernel@vger.kernel.org" , "H. Peter Anvin" , "J. Bruce Fields" , Theodore Ts'o , Alexander Viro , Andreas Dilger , Andrew Morton , Dave Chinner , Dave Hansen , Ingo Molnar , Jan Kara , Jeff Layton , Matthew Wilcox , Matthew Wilcox , Thomas Gleixner , linux-ext4 , linux-fsdevel , Linux MM , "linux-nvdimm@lists.01.org" , X86 ML , XFS Developers On Wed, Jan 6, 2016 at 10:00 AM, Ross Zwisler wrote: > __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, I'm assuming there's no danger of a such a buffer_head ever being used for the bdev parameter to dax_map_atomic()? Shouldn't we also/instead go fix ext4 to not send partially filled buffer_heads? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org