From: Ross Zwisler Subject: [PATCH v8 1/9] dax: fix NULL pointer dereference in __dax_dbg() Date: Thu, 7 Jan 2016 22:27:51 -0700 Message-ID: <1452230879-18117-2-git-send-email-ross.zwisler@linux.intel.com> References: <1452230879-18117-1-git-send-email-ross.zwisler@linux.intel.com> 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@lists.01.org, x86@kernel.org, xfs@oss.sgi.com To: linux-kernel@vger.kernel.org Return-path: In-Reply-To: <1452230879-18117-1-git-send-email-ross.zwisler@linux.intel.com> Sender: owner-linux-mm@kvack.org List-Id: linux-ext4.vger.kernel.org In __dax_pmd_fault() we currently assume that get_block() will always set bh.b_bdev and we unconditionally dereference it in __dax_dbg(). 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, initialize bh.b_bdev before passing bh into get_block(). It is possible that the filesystem's get_block() will update bh.b_bdev, and this is fine - we just want to initialize bh.b_bdev to something reasonable so that the calls to __dax_dbg() work and print something useful. Signed-off-by: Ross Zwisler Cc: Dan Williams --- fs/dax.c | 1 + 1 file changed, 1 insertion(+) diff --git a/fs/dax.c b/fs/dax.c index 7af8797..513bba5 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -624,6 +624,7 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, } memset(&bh, 0, sizeof(bh)); + bh.b_bdev = inode->i_sb->s_bdev; block = (sector_t)pgoff << (PAGE_SHIFT - blkbits); bh.b_size = PMD_SIZE; -- 2.5.0 -- 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