Re: Searching for initialisation of variables by function calls before null pointer checks

Markus Elfring
2020-06-29T16:20:36Z

> Some pointers are dereferenced before successful checks.

A source code place can be pointed out in an acceptable time frame for
a single file by the following script variant for the semantic patch language.

@display@
expression action1, action2;
expression* pointer1, pointer2;
identifier result1, result2;
statement is, es;
type t1, t2;
@@
t1 result1 = <+...
* action1(..., pointer1, ...)
...+>;
... when any
when != pointer1
t2 result2 = <+...
* action2(..., pointer2, ...)
...+>;
... when any
when != pointer1
when != pointer2
*if (!pointer1 || !pointer2 || ...)
is
else
es

elfring@Sonne:~/Projekte/Linux/next-patched> time spatch --profile --no-loops drivers/usb/mtu3/mtu3_gadget.c ~/Projekte/Coccinelle/janitor/show_pointer_usage_before_null_check11.cocci
…
@@ -332,14 +332,11 @@ error:

static int mtu3_gadget_dequeue(struct usb_ep *ep, struct usb_request *req)
{
- struct mtu3_ep *mep = to_mtu3_ep(ep);
- struct mtu3_request *mreq = to_mtu3_request(req);
struct mtu3_request *r;
unsigned long flags;
int ret = 0;
struct mtu3 *mtu = mep->mtu;

- if (!ep || !req || mreq->mep != mep)
return -EINVAL;

dev_dbg(mtu->dev, "%s : req=%p\n", __func__, req);
---------------------
profiling result
---------------------
Main total : 2.030205 sec 1 count
Main.outfiles computation : 1.648542 sec 1 count
…
real 0m2,122s
user 0m1,977s
sys 0m0,037s

I have tried this analysis approach out also for source files from
the software “Linux next-20200626”.

elfring@Sonne:~/Projekte/Linux/next-patched> XX=$(date) && spatch --no-loops --timeout 12 -j 4 --chunksize 1 -dir ~/Projekte/Linux/next-patched ~/Projekte/Coccinelle/janitor/show_pointer_usage_before_null_check11.cocci > ~/Projekte/Bau/Linux/scripts/Coccinelle/null/next/20200626/show_pointer_usage_before_null_check11.diff 2> ~/Projekte/Bau/Linux/scripts/Coccinelle/null/next/20200626/show_pointer_usage_before_null_check11-errors.txt; YY=$(date) && echo "$XX | $YY"
Mo 29. Jun 13:54:54 CEST 2020 | Mo 29. Jun 17:22:37 CEST 2020

Unfortunately, a lot of “exceptional” data processing results were logged then.

elfring@Sonne:~/Projekte/Bau/Linux/scripts/Coccinelle/null/next/20200626> grep 'EXN: Coccinelle_modules.Common.Timeout' show_pointer_usage_before_null_check11-errors.txt | wc -l
454

Will such a test run trigger any further development considerations?

Regards,
Markus