Re: [CHECKER] potential dereference of user pointer errors

[Chris Wright <chris@wirex.com>]

* Junfeng Yang (yjf@stanford.edu) wrote:
> 
> [BUG] not sure. the dereference occurs at a tainted place. call
> copy_from_user (, data, ), then copy_from_user (, *data, )
> 
> /home/junfeng/linux-2.5.63/sound/core/seq/instr/ainstr_iw.c:92:snd_seq_iwffff_copy_env_from_stream:
> ERROR:TAINTED deferencing "data" tainted by [dist=0][copy_from_user:parm1]

seems like a bug, although i think it's the first copy_from_user that
would be broken.

Looks like call flow could be something like:
Store user buf ptr in event.data.ext.ptr.
Call snd_seq_iwffff_put with the event.data.ext.ptr (offset by header bits)
Call snd_seq_iwffff_copy_env_from_stream with &event.data.ext.ptr (offset a
little further).

Finally, call copy_from_user on &event.data.ext.ptr, which is copying
into an stype.  This looks like it's the bug.   I don't think the 32 bit
addr should be copied into the stype, rather the 1st 32bits of the data
(IOW copy_from_user(stype, *data,...)).  The second copy_from_user (with
*data) copies in the whole iwffff_env_record_t struct which begins with
an stype, so it really looks as if the first copy is broken. Patch
below.   Jaroslav?

thanks,
-chris
-- 
Linux Security Modules     http://lsm.immunix.org     http://lsm.bkbits.net

===== instr/ainstr_iw.c 1.3 vs edited =====
--- 1.3/sound/core/seq/instr/ainstr_iw.c	Mon Feb 10 02:39:27 2003
+++ edited/instr/ainstr_iw.c	Fri Mar 21 13:01:32 2003
@@ -78,7 +78,7 @@
 	while (1) {
 		if (*len < (long)sizeof(__u32))
 			return -EINVAL;
-		if (copy_from_user(&stype, data, sizeof(stype)))
+		if (copy_from_user(&stype, *data, sizeof(stype)))
 			return -EFAULT;
 		if (stype == IWFFFF_STRU_WAVE)
 			return 0;