usx2y_urb_play_prepare() sums the packet lengths of a whole URB, copies that many frames with a single wrap, and sizes each playback packet from the capture packet's actual_length. Three things are unchecked: that the URB fits in the ring buffer, that a packet fits in the playback endpoint's maxpacksize, from which tmpbuf is allocated, and that actual_length is a whole number of frames. The ISO descriptors take the raw actual_length while transfer_buffer_length and the copies take count * stride, so a packet that is not a multiple of the stride makes the descriptors add up to more than the buffer, by up to stride - 1 bytes per packet. Return -EPIPE, as the existing packet-size check does, when the URB is larger than the buffer or a packet is larger than maxpacksize, and size each descriptor from whole frames, so the descriptors add up to transfer_buffer_length and each stays within maxpacksize. The buffer case is prevented by the previous patch and this is the guard for it; the other two depend only on the device. The first case is reachable on the unpatched driver with ordinary packets: on 7.3-rc7, a USB/IP device presenting the US-122 interface layout and sending 48-frame packets, with a 100-frame playback buffer (two 50-frame periods, inside the stock constraints), KASAN reports: BUG: KASAN: out-of-bounds in i_usx2y_urb_complete+0x79b/0x1ac0 Read of size 18446744073709551280 at addr ffff88800e6b02e0 by task vhci_rx/80 With both patches, the same device and a 200-frame playback buffer is refused at hw_params with EINVAL, and a 400-frame buffer plays for 30 s with the position advancing inside the buffer, no KASAN report and neither guard message. The maxpacksize check is not exercised: the emulated device reports the same wMaxPacketSize on both endpoints. The descriptor case is visible with capture packets of 195 bytes at stride 4 (48 frames and 3 bytes): without this change the four descriptors add up to 780 bytes for 768 bytes of data, and USB/IP's completion check refuses the URB ("total length of iso packets 780 not equal to actual length of buffer 768", -EPROTO), after which the driver stops the streams. With this patch every descriptor is 192 bytes, the descriptors add up to the data in every URB for 30 s, the position advances inside the buffer and KASAN reports nothing. The 48-frame playback run above is unchanged. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Signed-off-by: Sinan Turunc --- v4: size the ISO descriptors from whole frames, so they add up to transfer_buffer_length (review of v3); the maxpacksize check has its own ratelimited message. Regenerated on top of 1/2. v3: new patch, split out of the v3 draft; the review of v2 found both unchecked assumptions. The buffer case is confirmed on the unpatched driver and the guards tested on 7.3-rc7, see above. sound/usb/usx2y/usbusx2yaudio.c | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) diff --git a/sound/usb/usx2y/usbusx2yaudio.c b/sound/usb/usx2y/usbusx2yaudio.c index 1e1d0cfbd16..798c9bb5386 100644 --- a/sound/usb/usx2y/usbusx2yaudio.c +++ b/sound/usb/usx2y/usbusx2yaudio.c @@ -118,14 +118,31 @@ static int usx2y_urb_play_prepare(struct snd_usx2y_substream *subs, __func__, counts); return -EPIPE; } + if (counts * usx2y->stride > subs->maxpacksize) { + dev_err_ratelimited(&usx2y->dev->dev, + "%s: packet of %i bytes exceeds maxpacksize %u\n", + __func__, counts * usx2y->stride, + subs->maxpacksize); + return -EPIPE; + } /* set up descriptor */ urb->iso_frame_desc[pack].offset = pack ? urb->iso_frame_desc[pack - 1].offset + urb->iso_frame_desc[pack - 1].length : 0; - urb->iso_frame_desc[pack].length = cap_urb->iso_frame_desc[pack].actual_length; + urb->iso_frame_desc[pack].length = counts * usx2y->stride; } if (atomic_read(&subs->state) >= STATE_PRERUNNING) { + /* + * The copy below wraps once, which needs count <= buffer_size. + * snd_usx2y_pcm_open() guarantees it; guard anyway. + */ + if (unlikely(count > runtime->buffer_size)) { + dev_err_ratelimited(&usx2y->dev->dev, + "%s: URB of %i frames exceeds %lu-frame buffer, stopping\n", + __func__, count, runtime->buffer_size); + return -EPIPE; + } if (subs->hwptr + count > runtime->buffer_size) { /* err, the transferred area goes over buffer boundary. * copy the data to the temp buffer. -- 2.56.0