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Message-Id: <1452230879-18117-2-git-send-email-ross.zwisler@linux.intel.com>
Date: Thu, 7 Jan 2016 22:27:51 -0700
From: Ross Zwisler <ross.zwisler@...ux.intel.com>
To: linux-kernel@...r.kernel.org
Cc: Ross Zwisler <ross.zwisler@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>,
"J. Bruce Fields" <bfields@...ldses.org>,
"Theodore Ts'o" <tytso@....edu>,
Alexander Viro <viro@...iv.linux.org.uk>,
Andreas Dilger <adilger.kernel@...ger.ca>,
Andrew Morton <akpm@...ux-foundation.org>,
Dan Williams <dan.j.williams@...el.com>,
Dave Chinner <david@...morbit.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Ingo Molnar <mingo@...hat.com>, Jan Kara <jack@...e.com>,
Jeff Layton <jlayton@...chiereds.net>,
Matthew Wilcox <matthew.r.wilcox@...el.com>,
Matthew Wilcox <willy@...ux.intel.com>,
Thomas Gleixner <tglx@...utronix.de>,
linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-mm@...ck.org, linux-nvdimm@...ts.01.org, x86@...nel.org,
xfs@....sgi.com
Subject: [PATCH v8 1/9] dax: fix NULL pointer dereference in __dax_dbg()
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 <ross.zwisler@...ux.intel.com>
Cc: Dan Williams <dan.j.williams@...el.com>
---
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
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