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    Subject[PATCH 6/6] sysfs: fix off-by-one error in fill_read_buffer()
    Date
    From: Miao Xie <miaox@cn.fujitsu.com>

    I found that there is a off-by-one problem in the following code.

    Version: 2.6.24-rc2
    File: fs/sysfs/file.c:118-122
    Function: fill_read_buffer
    --------------------------------------------------------------------
    count = ops->show(kobj, attr_sd->s_attr.attr, buffer->page);

    sysfs_put_active_two(attr_sd);

    BUG_ON(count > (ssize_t)PAGE_SIZE);
    --------------------------------------------------------------------

    Because according to the specification of the sysfs and the implement of
    the show methods, the show methods return the number of bytes which would
    be generated for the given input, excluding the trailing null.So if the
    return value of the show methods equals PAGE_SIZE - 1, the buffer is full
    in fact. And if the return value equals PAGE_SIZE, the resulting string
    was already truncated,or buffer overflow occurred.

    This patch fixes an off-by-one error in fill_read_buffer.

    Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Acked-by: Tejun Heo <teheo@suse.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
    ---
    fs/sysfs/file.c | 6 +++++-
    1 files changed, 5 insertions(+), 1 deletions(-)

    diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
    index 27d1785..4045bdc 100644
    --- a/fs/sysfs/file.c
    +++ b/fs/sysfs/file.c
    @@ -119,7 +119,11 @@ static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer

    sysfs_put_active_two(attr_sd);

    - BUG_ON(count > (ssize_t)PAGE_SIZE);
    + /*
    + * The code works fine with PAGE_SIZE return but it's likely to
    + * indicate truncated result or overflow in normal use cases.
    + */
    + BUG_ON(count >= (ssize_t)PAGE_SIZE);
    if (count >= 0) {
    buffer->needs_read_fill = 0;
    buffer->count = count;
    --
    1.5.3.4
    -
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