Em Tue, 8 Jan 2019 15:40:47 +0200 Sakari Ailus <[email protected]> escreveu:
> On Tue, Jan 08, 2019 at 10:59:55AM -0200, Mauro Carvalho Chehab wrote: > > Em Tue, 8 Jan 2019 10:52:12 -0200 > > Mauro Carvalho Chehab <[email protected]> escreveu: > > > > > Em Tue, 8 Jan 2019 10:58:34 +0200 > > > Sakari Ailus <[email protected]> escreveu: > > > > > > > PAGE_ALIGN() may wrap the buffer size around to 0. Prevent this by > > > > checking that the aligned value is not smaller than the unaligned one. > > > > > > > > Note on backporting to stable: the file used to be under > > > > drivers/media/v4l2-core, it was moved to the current location after > > > > 4.14. > > > > > > > > Signed-off-by: Sakari Ailus <[email protected]> > > > > Cc: [email protected] > > > > Reviewed-by: Hans Verkuil <[email protected]> > > > > --- > > > > drivers/media/common/videobuf2/videobuf2-core.c | 4 ++++ > > > > 1 file changed, 4 insertions(+) > > > > > > > > diff --git a/drivers/media/common/videobuf2/videobuf2-core.c > > > > b/drivers/media/common/videobuf2/videobuf2-core.c > > > > index 0ca81d495bda..0234ddbfa4de 100644 > > > > --- a/drivers/media/common/videobuf2/videobuf2-core.c > > > > +++ b/drivers/media/common/videobuf2/videobuf2-core.c > > > > @@ -207,6 +207,10 @@ static int __vb2_buf_mem_alloc(struct vb2_buffer > > > > *vb) > > > > for (plane = 0; plane < vb->num_planes; ++plane) { > > > > unsigned long size = > > > > PAGE_ALIGN(vb->planes[plane].length); > > > > > > > > + /* Did it wrap around? */ > > > > + if (size < vb->planes[plane].length) > > > > + goto free; > > > > + > > > > > > Sorry, but I can't see how this could ever happen (except for a very > > > serious > > > bug at the compiler or at the hardware). > > > > > > See, the definition at PAGE_ALIGN is (from mm.h): > > > > > > #define PAGE_ALIGN(addr) ALIGN(addr, PAGE_SIZE) > > > > > > and the macro it uses come from kernel.h: > > > > > > #define __ALIGN_KERNEL(x, a) __ALIGN_KERNEL_MASK(x, > > > (typeof(x))(a) - 1) > > > #define __ALIGN_KERNEL_MASK(x, mask) (((x) + (mask)) & ~(mask)) > > > .. > > > #define ALIGN(x, a) __ALIGN_KERNEL((x), (a)) > > > > > > So, this: > > > size = PAGE_ALIGN(length); > > > > > > (assuming PAGE_SIZE= 0x1000) > > > > > > becomes: > > > > > > size = (length + 0x0fff) & ~0xfff; > > > > > > so, size will *always* be >= length. > > > > Hmm... after looking at patch 2, now I understand what's your concern... > > > > If someone indeed uses length = INT_MAX, size will indeed be zero. > > > > Please adjust the description accordingly, as it doesn't reflect > > that. > > How about: > > PAGE_ALIGN() may wrap the buffer length around to 0 if the value to be > aligned is close to the top of the value range of the type. Prevent this by > checking that the aligned value is not smaller than the unaligned one. I would be a way more clear, as this is there to prevent a single special case: length == ULEN_MAX. Something like: If one tried to allocate a buffer with sizeof(ULEN_MAX), this will cause an overflow at PAGE_ALIGN(), making it return zero as the size of the buffer, causing the code to fail. I would even let it clearer at the code itself. So, instead of the hunk you proposed, I would do: unsigned long size = vb->planes[plane].length; /* Prevent PAGE_ALIGN overflow */ if (WARN_ON(size == ULONG_MAX)) goto free; size = PAGE_ALIGN(vb->planes[plane].length); Thanks, Mauro
