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
