[PATCH v1] v4l2: v4l2_compat: Fix redirect from `__open(at)64_2()`

[Laurent Pinchart]

On Mon, Jun 17, 2024 at 11:37:53PM +0100, Kieran Bingham wrote:
> Quoting Barnabás Pőcze (2024-06-17 22:43:45)
> > `__open64_2()` and `__openat64_2()` should redirect
> > to `open64()` and `openat64()`, respectively, otherwise
> > the `O_LARGEFILE` flag will not be applied.
> > 
> > Fixes: 1023107b6405 ("v4l2: v4l2_compat: Intercept open64, openat64, and mmap64")
> > Signed-off-by: Barnabás Pőcze <pobrn at protonmail.com>
> 
> CI is all green here.
> https://gitlab.freedesktop.org/camera/libcamera/-/pipelines/1203630 
> 
> But commit 1023107b6405 ("v4l2: v4l2_compat: Intercept open64, openat64, and mmap64")
> states:
> 
>     Also, since we set _FILE_OFFSET_BITS to 32 to force the various open and
>     mmap symbols that we export to not be the 64-bit versions, our dlsym to
>     get the original open and mmap calls will not automatically be converted
>     to their 64-bit versions. Since we intercept both 32-bit and 64-bit
>     versions of open and mmap, we should be using the 64-bit version to
>     service both. Fetch the 64-bit versions of openat and mmap directly.
> 
> is that why these were the non-64 bit variants?

With _FORTIFY_SOURCE, we end up servicing both the 32-bit and 64-bit
versions with the 32-bit wrappers, which then call openat64() that we
dlsym()ed and stored in V4L2CompatManager::openat. That part is fine,
but going through the 32-bit wrappers mean we don't pass O_LARGEFILE to
openat64() when called from __open64_2() or __openat64_2(). That's
wrong, as it will prevent, on 32-bit platforms, file sizes larger than
4GB.

> This feels like it's "too obvious" ... I wonder what we missed ...
> 
> Paul? Any insights? (It was ... a long time ago that you wrote that
> patch)

I think the patch is right, it seems to have been an oversight.

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

> > ---
> >  src/v4l2/v4l2_compat.cpp | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/src/v4l2/v4l2_compat.cpp b/src/v4l2/v4l2_compat.cpp
> > index 8e2b7e92..8a44403e 100644
> > --- a/src/v4l2/v4l2_compat.cpp
> > +++ b/src/v4l2/v4l2_compat.cpp
> > @@ -59,7 +59,7 @@ LIBCAMERA_PUBLIC int open64(const char *path, int oflag, ...)
> >  
> >  LIBCAMERA_PUBLIC int __open64_2(const char *path, int oflag)
> >  {
> > -       return open(path, oflag);
> > +       return open64(path, oflag);
> >  }
> >  #endif
> >  
> > @@ -90,7 +90,7 @@ LIBCAMERA_PUBLIC int openat64(int dirfd, const char *path, int oflag, ...)
> >  
> >  LIBCAMERA_PUBLIC int __openat64_2(int dirfd, const char *path, int oflag)
> >  {
> > -       return openat(dirfd, path, oflag);
> > +       return openat64(dirfd, path, oflag);
> >  }
> >  #endif
> >  

-- 
Regards,

Laurent Pinchart