Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Content-Type: text/plain; charset="UTF-8"
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
MIME-Version: 1.0
From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org, Denis Kirjanov <kda@linux-powerpc.org>,
        "Theodore Ts'o" <tytso@mit.edu>
Date:   Tue, 02 Apr 2019 14:38:28 +0100
Message-ID: <lsq.1554212308.391030814@decadent.org.uk>
Subject: [PATCH 3.16 81/99] ext4: fix a potential fiemap/page fault
 deadlock w/ inline_data
In-Reply-To: <lsq.1554212307.17110877@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

3.16.65-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Theodore Ts'o <tytso@mit.edu>

commit 2b08b1f12cd664dc7d5c84ead9ff25ae97ad5491 upstream.

The ext4_inline_data_fiemap() function calls fiemap_fill_next_extent()
while still holding the xattr semaphore.  This is not necessary and it
triggers a circular lockdep warning.  This is because
fiemap_fill_next_extent() could trigger a page fault when it writes
into page which triggers a page fault.  If that page is mmaped from
the inline file in question, this could very well result in a
deadlock.

This problem can be reproduced using generic/519 with a file system
configuration which has the inline_data feature enabled.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 fs/ext4/inline.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -1846,12 +1846,12 @@ int ext4_inline_data_fiemap(struct inode
 	physical += (char *)ext4_raw_inode(&iloc) - iloc.bh->b_data;
 	physical += offsetof(struct ext4_inode, i_block);
 
-	if (physical)
-		error = fiemap_fill_next_extent(fieinfo, start, physical,
-						inline_len, flags);
 	brelse(iloc.bh);
 out:
 	up_read(&EXT4_I(inode)->xattr_sem);
+	if (physical)
+		error = fiemap_fill_next_extent(fieinfo, start, physical,
+						inline_len, flags);
 	return (error < 0 ? error : 0);
 }