I think need Cc to Lad, Prabhakar <prabhakar.csengg@xxxxxxxxx> On 10/30/2018 02:46 AM, Wenwen Wang wrote: > 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 >>
