On Wed, Mar 20, 2013 at 9:25 AM, Ming Lei <ming....@canonical.com> wrote:
> In case of 'if (filp->f_pos == 0 or 1)' of sysfs_readdir(),
> the failure from filldir() isn't handled, and the reference counter
> of the sysfs_dirent object pointed by filp->private_data will be
> released without clearing filp->private_data, so use after free
> bug will be triggered later.
>
> This patch returns immeadiately under the situation for fixing the bug,
> and it is reasonable to return from readdir() when filldir() fails.
>
> Reported-by: Dave Jones <da...@redhat.com>
> Tested-by: Sasha Levin <levinsasha...@gmail.com>
> Cc: <sta...@vger.kernel.org>
> Signed-off-by: Ming Lei <ming....@canonical.com>
> ---
> fs/sysfs/dir.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
> index c9e1660..e145126 100644
> --- a/fs/sysfs/dir.c
> +++ b/fs/sysfs/dir.c
> @@ -1020,6 +1020,8 @@ static int sysfs_readdir(struct file * filp, void *
> dirent, filldir_t filldir)
> ino = parent_sd->s_ino;
> if (filldir(dirent, ".", 1, filp->f_pos, ino, DT_DIR) == 0)
> filp->f_pos++;
> + else
> + return 0;
> }
> if (filp->f_pos == 1) {
> if (parent_sd->s_parent)
> @@ -1028,6 +1030,8 @@ static int sysfs_readdir(struct file * filp, void *
> dirent, filldir_t filldir)
> ino = parent_sd->s_ino;
> if (filldir(dirent, "..", 2, filp->f_pos, ino, DT_DIR) == 0)
> filp->f_pos++;
> + else
> + return 0;
> }
Looks good to me. This is just an observation. readdir callers are
checking against NULL as opposed 0. Not a problem really probably
since NULL is defined as 0.
-- Shuah
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