4.19-stable review patch. If anyone has any objections, please let me know.
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From: Dan Carpenter dan.carpenter@linaro.org
[ Upstream commit faa4364bef2ec0060de381ff028d1d836600a381 ]
The subtract in this condition is reversed. The ->length is the length of the buffer. The ->bytesused is how many bytes we have copied thus far. When the condition is reversed that means the result of the subtraction is always negative but since it's unsigned then the result is a very high positive value. That means the overflow check is never true.
Additionally, the ->bytesused doesn't actually work for this purpose because we're not writing to "buf->mem + buf->bytesused". Instead, the math to calculate the destination where we are writing is a bit involved. You calculate the number of full lines already written, multiply by two, skip a line if necessary so that we start on an odd numbered line, and add the offset into the line.
To fix this buffer overflow, just take the actual destination where we are writing, if the offset is already out of bounds print an error and return. Otherwise, write up to buf->length bytes.
Fixes: 9cb2173e6ea8 ("[media] media: Add stk1160 new driver (easycap replacement)") Signed-off-by: Dan Carpenter dan.carpenter@linaro.org Reviewed-by: Ricardo Ribalda ribalda@chromium.org Signed-off-by: Hans Verkuil hverkuil-cisco@xs4all.nl Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/media/usb/stk1160/stk1160-video.c | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-)
diff --git a/drivers/media/usb/stk1160/stk1160-video.c b/drivers/media/usb/stk1160/stk1160-video.c index 0e98b450ae01b..687c7b6a0c303 100644 --- a/drivers/media/usb/stk1160/stk1160-video.c +++ b/drivers/media/usb/stk1160/stk1160-video.c @@ -109,7 +109,7 @@ void stk1160_buffer_done(struct stk1160 *dev) static inline void stk1160_copy_video(struct stk1160 *dev, u8 *src, int len) { - int linesdone, lineoff, lencopy; + int linesdone, lineoff, lencopy, offset; int bytesperline = dev->width * 2; struct stk1160_buffer *buf = dev->isoc_ctl.buf; u8 *dst = buf->mem; @@ -149,8 +149,13 @@ void stk1160_copy_video(struct stk1160 *dev, u8 *src, int len) * Check if we have enough space left in the buffer. * In that case, we force loop exit after copy. */ - if (lencopy > buf->bytesused - buf->length) { - lencopy = buf->bytesused - buf->length; + offset = dst - (u8 *)buf->mem; + if (offset > buf->length) { + dev_warn_ratelimited(dev->dev, "out of bounds offset\n"); + return; + } + if (lencopy > buf->length - offset) { + lencopy = buf->length - offset; remain = lencopy; }
@@ -192,8 +197,13 @@ void stk1160_copy_video(struct stk1160 *dev, u8 *src, int len) * Check if we have enough space left in the buffer. * In that case, we force loop exit after copy. */ - if (lencopy > buf->bytesused - buf->length) { - lencopy = buf->bytesused - buf->length; + offset = dst - (u8 *)buf->mem; + if (offset > buf->length) { + dev_warn_ratelimited(dev->dev, "offset out of bounds\n"); + return; + } + if (lencopy > buf->length - offset) { + lencopy = buf->length - offset; remain = lencopy; }