On Mon, May 19, 2014 at 03:52:10PM -0400, Tejun Heo wrote:
> 13c589d5b0ac ("sysfs: use seq_file when reading regular files")
> switched sysfs from custom read implementation to seq_file to enable
> later transition to kernfs. After the change, the buffer passed to
> ->show() is acquired through seq_get_buf(); unfortunately, this
> introduces a subtle behavior change. Before the commit, the buffer
> passed to ->show() was always zero as it was allocated using
> get_zeroed_page(). Because seq_file doesn't clear buffers on
> allocation and neither does seq_get_buf(), after the commit, depending
> on the behavior of ->show(), we may end up exposing uninitialized data
> to userland thus possibly altering userland visible behavior and
> leaking information.
>
> Fix it by explicitly clearing the buffer.
>
> Signed-off-by: Tejun Heo <[email protected]>
> Reported-by: Ron <[email protected]>
> Fixes: 13c589d5b0ac ("sysfs: use seq_file when reading regular files")
> ---
> fs/sysfs/file.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
> index 28cc1acd..e9ef59b 100644
> --- a/fs/sysfs/file.c
> +++ b/fs/sysfs/file.c
> @@ -47,12 +47,13 @@ static int sysfs_kf_seq_show(struct seq_file *sf, void *v)
> ssize_t count;
> char *buf;
>
> - /* acquire buffer and ensure that it's >= PAGE_SIZE */
> + /* acquire buffer and ensure that it's >= PAGE_SIZE and clear */
> count = seq_get_buf(sf, &buf);
> if (count < PAGE_SIZE) {
> seq_commit(sf, -1);
> return 0;
> }
> + memset(buf, 0, PAGE_SIZE);
>
> /*
> * Invoke show(). Control may reach here via seq file lseek even
Thanks, I'll go queue this up.
greg k-h
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