diff options
author | John Hubbard <jhubbard@nvidia.com> | 2020-05-21 21:15:05 -0700 |
---|---|---|
committer | Sam Ravnborg <sam@ravnborg.org> | 2020-05-31 22:54:33 +0200 |
commit | e2e1c7bda4445363027a4ceed1cc3a8ccc2472a9 (patch) | |
tree | 52345346eb2fe44c723afd9971f20d359210b8fd /drivers/video/fbdev | |
parent | 5a4784f49b2dcfff888f0ac97b981224c57c55fc (diff) |
video: fbdev: fix error handling for get_user_pages_fast()
Dealing with the return value of get_user_pages*() variants has a few
classic pitfalls, and this driver found one of them: the return value
might be zero, positive, or -errno. And if positive, it might be fewer
pages than were requested. And if fewer pages than requested, then
the caller should return (via put_page()) the pages that *were*
pinned.
This driver was doing that *except* that it had a problem with the
-errno case, which was being stored in an unsigned int, and which
would case an interesting mess if it ever happened: nr_pages would be
interpreted as a spectacularly huge unsigned value, rather than a
small negative value. Also, it was unnecessarily overriding a
potentially informative -errno, with -EINVAL, in some cases.
Instead: clamp the nr_pages to zero or positive, so that the error
handling works. And return the -errno value from get_user_pages*(),
unchanged, if we get one. And explain this with comments, seeing as
how it is error-prone.
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Gustavo A. R. Silva <gustavo@embeddedor.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-fbdev@vger.kernel.org
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200522041506.39638-2-jhubbard@nvidia.com
Diffstat (limited to 'drivers/video/fbdev')
-rw-r--r-- | drivers/video/fbdev/pvr2fb.c | 18 |
1 files changed, 16 insertions, 2 deletions
diff --git a/drivers/video/fbdev/pvr2fb.c b/drivers/video/fbdev/pvr2fb.c index f18d457175d9..ceb6ef590597 100644 --- a/drivers/video/fbdev/pvr2fb.c +++ b/drivers/video/fbdev/pvr2fb.c @@ -654,8 +654,22 @@ static ssize_t pvr2fb_write(struct fb_info *info, const char *buf, ret = get_user_pages_fast((unsigned long)buf, nr_pages, FOLL_WRITE, pages); if (ret < nr_pages) { - nr_pages = ret; - ret = -EINVAL; + if (ret < 0) { + /* + * Clamp the unsigned nr_pages to zero so that the + * error handling works. And leave ret at whatever + * -errno value was returned from GUP. + */ + nr_pages = 0; + } else { + nr_pages = ret; + /* + * Use -EINVAL to represent a mildly desperate guess at + * why we got fewer pages (maybe even zero pages) than + * requested. + */ + ret = -EINVAL; + } goto out_unmap; } |