From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from userp2120.oracle.com ([156.151.31.85]:54146 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750764AbeDQFjM (ORCPT ); Tue, 17 Apr 2018 01:39:12 -0400 Date: Mon, 16 Apr 2018 22:39:07 -0700 From: "Darrick J. Wong" Subject: [PATCH v2] xfs: prevent creating negative-sized file via INSERT_RANGE Message-ID: <20180417053907.GE5203@magnolia> References: <20180416204630.177682-1-ebiggers3@gmail.com> <20180417005218.GC5203@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180417005218.GC5203@magnolia> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: Eric Biggers Cc: linux-xfs@vger.kernel.org, Eric Biggers How about this instead? --D --- From: Eric Biggers During the "insert range" fallocate operation, i_size grows by the specified 'len' bytes. XFS verifies that i_size + len < s_maxbytes, as it should. But this comparison is done using the signed 'loff_t', and 'i_size + len' can wrap around to a negative value, causing the check to incorrectly pass, resulting in an inode with "negative" i_size. This is possible on 64-bit platforms, where XFS sets s_maxbytes = LLONG_MAX. ext4 and f2fs don't run into this because they set a smaller s_maxbytes. Fix it by doing an unsigned comparison instead. Reproducer: xfs_io -f file -c "truncate $(((1<<63)-1))" -c "finsert 0 4096" Fixes: a904b1ca5751 ("xfs: Add support FALLOC_FL_INSERT_RANGE for fallocate") Cc: # v4.1+ Signed-off-by: Eric Biggers Reviewed-by: Darrick J. Wong [darrick: rearrange this whole function to use subtraction to avoid overflow of the signed integer addition] Signed-off-by: Darrick J. Wong --- fs/xfs/xfs_file.c | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c index 9fd9dd7..a385334 100644 --- a/fs/xfs/xfs_file.c +++ b/fs/xfs/xfs_file.c @@ -779,21 +779,27 @@ xfs_file_fallocate( goto out_unlock; } else if (mode & FALLOC_FL_INSERT_RANGE) { unsigned int blksize_mask = i_blocksize(inode) - 1; + loff_t isize; - new_size = i_size_read(inode) + len; - if (offset & blksize_mask || len & blksize_mask) { - error = -EINVAL; + isize = i_size_read(inode); + + /* + * New inode size must not exceed ->s_maxbytes, accounting for + * possible signed overflow. + */ + if (inode->i_sb->s_maxbytes - isize < len) { + error = -EFBIG; goto out_unlock; } - /* check the new inode size does not wrap through zero */ - if (new_size > inode->i_sb->s_maxbytes) { - error = -EFBIG; + if (offset & blksize_mask || len & blksize_mask) { + error = -EINVAL; goto out_unlock; } + new_size = isize + len; /* Offset should be less than i_size */ - if (offset >= i_size_read(inode)) { + if (offset >= isize) { error = -EINVAL; goto out_unlock; }