[Cocci] Incorrect match with when != condition

[Cocci] Incorrect match with when != condition

[Denis Efremov]

Hi,

I'm trying to write the check to detect the absence of commit
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=51b2ee7d006a736a9126e8111d1f24e4fd0afaa6
in kernel. The pattern can be:

@err exists@
identifier namlen, dchild, dparent, exp;
position p;
statement S;
@@

compose_entry_fh(..., int namlen, ...)
{
	...
	if (namlen == 2) {
*		dchild =@p dget_parent(dparent);
		... when != dparent == exp->ex_path.dentry
	} else S
	...
}

But unfortunately, it matches even the fixed source. I think
that condition "... when != dparent == exp->ex_path.dentry" doesn't
work as expected. Steps to reproduce:

$ cd linux # latest master branch
$ wget https://raw.githubusercontent.com/evdenis/cvehound/b2d109c959c299dce10274c1806406fc5653e5d0/cvehound/cve/CVE-2021-3178.cocci
$ spatch -D detect --cocci-file CVE-2021-3178.cocci fs/nfsd/nfs3xdr.c
fs/nfsd/nfs3xdr.c:935:10-11: ERROR: CVE-2021-3178
diff =
--- fs/nfsd/nfs3xdr.c
+++ /tmp/cocci-output-526900-b87df1-nfs3xdr.c
@@ -932,7 +932,6 @@ compose_entry_fh(struct nfsd3_readdirres
  
         if (isdotent(name, namlen)) {
                 if (namlen == 2) {
			// !!! shouldn't match because of if (dparent == exp->ex_path.dentry) goto out; check after
-                       dchild = dget_parent(dparent);
                         /*
                          * Don't return filehandle for ".." if we're at
                          * the filesystem or export root:
$ spatch --version
spatch version 1.1.0 compiled with OCaml version 4.11.1

Thanks,
Denis
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Re: [Cocci] Incorrect match with when != condition

[Julia Lawall]

On Wed, 17 Mar 2021, Denis Efremov wrote:

> Hi,
>
> I'm trying to write the check to detect the absence of commit
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=51b2ee7d006a736a9126e8111d1f24e4fd0afaa6
> in kernel. The pattern can be:
>
> @err exists@
> identifier namlen, dchild, dparent, exp;
> position p;
> statement S;
> @@
>
> compose_entry_fh(..., int namlen, ...)
> {
> 	...
> 	if (namlen == 2) {
> *		dchild =@p dget_parent(dparent);
> 		... when != dparent == exp->ex_path.dentry

add when forall here.  There does exist a path that does not contain the
dparent == exp->ex_path.dentry test.  That is the path that takesthe first
goto out.

julia

> 	} else S
> 	...
> }
>
> But unfortunately, it matches even the fixed source. I think
> that condition "... when != dparent == exp->ex_path.dentry" doesn't
> work as expected. Steps to reproduce:
>
> $ cd linux # latest master branch
> $ wget
> https://raw.githubusercontent.com/evdenis/cvehound/b2d109c959c299dce10274c1806406fc5653e5d0/cvehound/cve/CVE-2021-3178.cocci
> $ spatch -D detect --cocci-file CVE-2021-3178.cocci fs/nfsd/nfs3xdr.c
> fs/nfsd/nfs3xdr.c:935:10-11: ERROR: CVE-2021-3178
> diff =
> --- fs/nfsd/nfs3xdr.c
> +++ /tmp/cocci-output-526900-b87df1-nfs3xdr.c
> @@ -932,7 +932,6 @@ compose_entry_fh(struct nfsd3_readdirres
>          if (isdotent(name, namlen)) {
>                 if (namlen == 2) {
> 			// !!! shouldn't match because of if (dparent ==
> exp->ex_path.dentry) goto out; check after
> -                       dchild = dget_parent(dparent);
>                         /*
>                          * Don't return filehandle for ".." if we're at
>                          * the filesystem or export root:
> $ spatch --version
> spatch version 1.1.0 compiled with OCaml version 4.11.1
>
> Thanks,
> Denis
>
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Re: [Cocci] Incorrect match with when != condition

[Denis Efremov]

On 3/17/21 11:32 PM, Julia Lawall wrote:
> 
> 
> On Wed, 17 Mar 2021, Denis Efremov wrote:
> 
>> Hi,
>>
>> I'm trying to write the check to detect the absence of commit
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit?id=51b2ee7d006a736a9126e8111d1f24e4fd0afaa6
>> in kernel. The pattern can be:
>>
>> @err exists@
>> identifier namlen, dchild, dparent, exp;
>> position p;
>> statement S;
>> @@
>>
>> compose_entry_fh(..., int namlen, ...)
>> {
>> 	...
>> 	if (namlen == 2) {
>> *		dchild =@p dget_parent(dparent);
>> 		... when != dparent == exp->ex_path.dentry
> 
> add when forall here.  There does exist a path that does not contain the
> dparent == exp->ex_path.dentry test.  That is the path that takesthe first
> goto out.

This solved the problem, thanks!
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