Hello, Can anyone confirm this bug? Thanks! Wenwen On Fri, Oct 19, 2018 at 9:12 AM Wenwen Wang <wang6495@xxxxxxx> wrote: > > In dvb_audio_write(), the first byte of the user-space buffer 'buf' is > firstly copied and checked to see whether this is a TS packet, which always > starts with 0x47 for synchronization purposes. If yes, ts_play() will be > called. Otherwise, dvb_aplay() will be called. In ts_play(), the content of > 'buf', including the first byte, is copied again from the user space. > However, after the copy, no check is re-enforced on the first byte of the > copied data. Given that 'buf' is in the user space, a malicious user can > race to change the first byte after the check in dvb_audio_write() but > before the copy in ts_play(). Through this way, the user can supply > inconsistent code, which can cause undefined behavior of the kernel and > introduce potential security risk. > > This patch adds a necessary check in ts_play() to make sure the first byte > acquired in the second copy contains the expected value. Otherwise, an > error code EINVAL will be returned. > > Signed-off-by: Wenwen Wang <wang6495@xxxxxxx> > --- > drivers/media/pci/ttpci/av7110_av.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/drivers/media/pci/ttpci/av7110_av.c b/drivers/media/pci/ttpci/av7110_av.c > index ef1bc17..1ff6062 100644 > --- a/drivers/media/pci/ttpci/av7110_av.c > +++ b/drivers/media/pci/ttpci/av7110_av.c > @@ -468,6 +468,8 @@ static ssize_t ts_play(struct av7110 *av7110, const char __user *buf, > } > if (copy_from_user(kb, buf, TS_SIZE)) > return -EFAULT; > + if (kb[0] != 0x47) > + return -EINVAL; > write_ts_to_decoder(av7110, type, kb, TS_SIZE); > todo -= TS_SIZE; > buf += TS_SIZE; > -- > 2.7.4 >
