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authorJohn Hubbard <jhubbard@nvidia.com>2020-05-21 21:15:05 -0700
committerSam Ravnborg <sam@ravnborg.org>2020-05-31 22:54:33 +0200
commite2e1c7bda4445363027a4ceed1cc3a8ccc2472a9 (patch)
tree52345346eb2fe44c723afd9971f20d359210b8fd /drivers/video/fbdev/pvr2fb.c
parent5a4784f49b2dcfff888f0ac97b981224c57c55fc (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/pvr2fb.c')
-rw-r--r--drivers/video/fbdev/pvr2fb.c18
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;
}