Hi Souptick, On 2019-01-25 05:55, Souptick Joarder wrote: > On Tue, Jan 22, 2019 at 8:37 PM Marek Szyprowski > <m.szyprowski@xxxxxxxxxxx> wrote: >> On 2019-01-11 16:11, Souptick Joarder wrote: >>> Convert to use vm_insert_range_buggy to map range of kernel memory >>> to user vma. >>> >>> This driver has ignored vm_pgoff. We could later "fix" these drivers >>> to behave according to the normal vm_pgoff offsetting simply by >>> removing the _buggy suffix on the function name and if that causes >>> regressions, it gives us an easy way to revert. >> Just a generic note about videobuf2: videobuf2-dma-sg is ignoring vm_pgoff by design. vm_pgoff is used as a 'cookie' to select a buffer to mmap and videobuf2-core already checks that. If userspace provides an offset, which doesn't match any of the registered 'cookies' (reported to userspace via separate v4l2 ioctl), an error is returned. > Ok, it means once the buf is selected, videobuf2-dma-sg should always > mapped buf->pages[i] > from index 0 ( irrespective of vm_pgoff value). So although we are > replacing the code with > vm_insert_range_buggy(), *_buggy* suffix will mislead others and > should not be used. > And if we replace this code with vm_insert_range(), this will > introduce bug for *non zero* > value of vm_pgoff. > > Please correct me if my understanding is wrong. You are correct. IMHO the best solution in this case would be to add following fix: diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c index 70e8c3366f9c..ca4577a7d28a 100644 --- a/drivers/media/common/videobuf2/videobuf2-core.c +++ b/drivers/media/common/videobuf2/videobuf2-core.c @@ -2175,6 +2175,13 @@ int vb2_mmap(struct vb2_queue *q, struct vm_area_struct *vma) goto unlock; } + /* + * vm_pgoff is treated in V4L2 API as a 'cookie' to select a buffer, + * not as a in-buffer offset. We always want to mmap a whole buffer + * from its beginning. + */ + vma->vm_pgoff = 0; + ret = call_memop(vb, mmap, vb->planes[plane].mem_priv, vma); unlock: diff --git a/drivers/media/common/videobuf2/videobuf2-dma-contig.c b/drivers/media/common/videobuf2/videobuf2-dma-contig.c index aff0ab7bf83d..46245c598a18 100644 --- a/drivers/media/common/videobuf2/videobuf2-dma-contig.c +++ b/drivers/media/common/videobuf2/videobuf2-dma-contig.c @@ -186,12 +186,6 @@ static int vb2_dc_mmap(void *buf_priv, struct vm_area_struct *vma) return -EINVAL; } - /* - * dma_mmap_* uses vm_pgoff as in-buffer offset, but we want to - * map whole buffer - */ - vma->vm_pgoff = 0; - ret = dma_mmap_attrs(buf->dev, vma, buf->cookie, buf->dma_addr, buf->size, buf->attrs); -- Then you can simply use non-buggy version of your function in drivers/media/common/videobuf2/videobuf2-dma-sg.c. I can send above as a formal patch if you want. > So what your opinion about this patch ? Shall I drop this patch from > current series ? > or, > There is any better way to handle this scenario ? > > >>> There is an existing bug inside gem_mmap_obj(), where user passed >>> length is not checked against buf->num_pages. For any value of >>> length > buf->num_pages it will end up overrun buf->pages[i], >>> which could lead to a potential bug. > It is not gem_mmap_obj(), it should be vb2_dma_sg_mmap(). > Sorry about it. > > What about this issue ? Does it looks like a valid issue ? It is already handled in vb2_mmap(). Such call will be rejected. > ... Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
