4.4-stable review patch. If anyone has any objections, please let me know.
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From: Wenwen Wang wang6495@umn.edu
commit 3f12888dfae2a48741c4caa9214885b3aaf350f9 upstream.
In snd_ctl_elem_add_compat(), the fields of the struct 'data' need to be copied from the corresponding fields of the struct 'data32' in userspace. This is achieved by invoking copy_from_user() and get_user() functions. The problem here is that the 'type' field is copied twice. One is by copy_from_user() and one is by get_user(). Given that the 'type' field is not used between the two copies, the second copy is *completely* redundant and should be removed for better performance and cleanup. Also, these two copies can cause inconsistent data: as the struct 'data32' resides in userspace and a malicious userspace process can race to change the 'type' field between the two copies to cause inconsistent data. Depending on how the data is used in the future, such an inconsistency may cause potential security risks.
For above reasons, we should take out the second copy.
Signed-off-by: Wenwen Wang wang6495@umn.edu Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@suse.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- sound/core/control_compat.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
--- a/sound/core/control_compat.c +++ b/sound/core/control_compat.c @@ -400,8 +400,7 @@ static int snd_ctl_elem_add_compat(struc if (copy_from_user(&data->id, &data32->id, sizeof(data->id)) || copy_from_user(&data->type, &data32->type, 3 * sizeof(u32))) goto error; - if (get_user(data->owner, &data32->owner) || - get_user(data->type, &data32->type)) + if (get_user(data->owner, &data32->owner)) goto error; switch (data->type) { case SNDRV_CTL_ELEM_TYPE_BOOLEAN: