Re: [PATCH] fbdev: fix possible NULL pointer derefernce

Hello,

2014-04-17 9:00 GMT+09:00 DaeSeok Youn [off-list ref]:

Hello,

2014-04-16 21:38 GMT+09:00 Jean-Christophe PLAGNIOL-VILLARD
[off-list ref]:

quoted

On Apr 16, 2014, at 5:40 PM, Daeseok Youn [off-list ref] wrote:

quoted

The spec->modedb can be NULL by fb_create_modedb().

And also smatch says:
drivers/video/fbdev/core/fbmon.c:975 fb_edid_to_monspecs() error:
potential null dereference 'specs->modedb'.
(fb_create_modedb returns null)

Signed-off-by: Daeseok Youn <redacted>
---
drivers/video/fbdev/core/fbmon.c |    3 +++
1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/drivers/video/fbdev/core/fbmon.c b/drivers/video/fbdev/core/fbmon.c
index c204ebe..db274ca 100644
--- a/drivers/video/fbdev/core/fbmon.c
+++ b/drivers/video/fbdev/core/fbmon.c

@@ -966,6 +966,9 @@ void fb_edid_to_monspecs(unsigned char *edid, struct fb_monspecs *specs)

      specs->modedb = fb_create_modedb(edid, &specs->modedb_len);

+     if (!specs->modedb)
+             return;
+

we need to return an error and trace it

Yes, you're right. I will change return type from void to int and add
to handle an error when this function(fb_edid_to_monspecs) is called.

I try to look at the fbdev code related with fb_edid_to_monspecs().
And the result, I think it doesn't need to return an error and trace it.
My patch is also useless because modedb_len is zero when
fb_create_modedb() returns NULL so It cannot be dereferenced.

And callers of this function seem to need a log but I think they don't need to
handling an error. Some functions are handling error with checking
NULL of modedb variable,
they are just printing an error message.

If I am wrong or you have reasons for handling an error on that
function, please let me know.

Regards,
Daeseok Youn.

I will send this patch as your comment.

Thanks for review.

Daeseok Youn.

quoted

Best Regards,
J.

quoted

      /*
       * Workaround for buggy EDIDs that sets that the first
       * detailed timing is preferred but has not detailed
--
1.7.4.4