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    Subject[PATCH 4.14 19/43] xfs: prevent creating negative-sized file via INSERT_RANGE
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

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

    From: Darrick J. Wong <darrick.wong@oracle.com>

    commit 7d83fb14258b9961920cd86f0b921caaeb3ebe85 upstream.

    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 using subtraction 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: <stable@vger.kernel.org> # v4.1+
    Originally-From: Eric Biggers <ebiggers@google.com>
    Signed-off-by: Eric Biggers <ebiggers@google.com>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
    [darrick: fix signed integer addition overflow too]
    Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/xfs/xfs_file.c | 14 +++++++++-----
    1 file changed, 9 insertions(+), 5 deletions(-)

    --- a/fs/xfs/xfs_file.c
    +++ b/fs/xfs/xfs_file.c
    @@ -811,22 +811,26 @@ xfs_file_fallocate(
    if (error)
    goto out_unlock;
    } else if (mode & FALLOC_FL_INSERT_RANGE) {
    - unsigned int blksize_mask = i_blocksize(inode) - 1;
    + unsigned int blksize_mask = i_blocksize(inode) - 1;
    + loff_t isize = i_size_read(inode);

    - new_size = i_size_read(inode) + len;
    if (offset & blksize_mask || len & blksize_mask) {
    error = -EINVAL;
    goto out_unlock;
    }

    - /* check the new inode size does not wrap through zero */
    - if (new_size > inode->i_sb->s_maxbytes) {
    + /*
    + * 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;
    }
    + 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;
    }

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