Re: [patch v2] sunrpc: integer underflow in rsc_parse()

["J. Bruce Fields" <bfields@fieldses.org>]

On Tue, Feb 24, 2015 at 10:54:44PM -0500, Simo Sorce wrote:
> On Tue, 2015-02-24 at 18:34 +0300, Dan Carpenter wrote:
> > If we call groups_alloc() with invalid values then it's might lead to
> > memory corruption.  For example, with a negative value then we might not
> > allocate enough for sizeof(struct group_info).
> > 
> > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > ---
> > v2:  In v1, I changed groups_alloc().  The other places which call
> > groups_alloc() check the value before calling.  Eric wanted that, either
> > have all the callers check, or all the callers rely on groups_alloc().
> > In the end, Bruce Fields said adding the check here was probably
> > reasonable.
> > 
> > diff --git a/net/sunrpc/auth_gss/svcauth_gss.c b/net/sunrpc/auth_gss/svcauth_gss.c
> > index 224a82f..1095be9 100644
> > --- a/net/sunrpc/auth_gss/svcauth_gss.c
> > +++ b/net/sunrpc/auth_gss/svcauth_gss.c
> > @@ -463,6 +463,8 @@ static int rsc_parse(struct cache_detail *cd,
> >  		/* number of additional gid's */
> >  		if (get_int(&mesg, &N))
> >  			goto out;
> > +		if (N < 0 || N > NGROUPS_MAX)
> > +			goto out;
> >  		status = -ENOMEM;
> >  		rsci.cred.cr_group_info = groups_alloc(N);
> >  		if (rsci.cred.cr_group_info == NULL)
> > --
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> 
> I touched this code relatively recently, and this check looks correct.
> Feel free to add Reviewed-by: Simo Sorce <simo@redhat.com>

Thanks!  I thought your below-the-line context was useful, so pulled a
version of it into the commit.

--b.

commit 76cb4be993c0
Author: Dan Carpenter <dan.carpenter@oracle.com>
Date:   Tue Feb 24 18:34:01 2015 +0300

    sunrpc: integer underflow in rsc_parse()
    
    If we call groups_alloc() with invalid values then it's might lead to
    memory corruption.  For example, with a negative value then we might not
    allocate enough for sizeof(struct group_info).
    
    (We're doing this in the caller for consistency with other callers of
    groups_alloc().  The other alternative might be to move the check out of
    all the callers into groups_alloc().)
    
    Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
    Reviewed-by: Simo Sorce <simo@redhat.com>
    Signed-off-by: J. Bruce Fields <bfields@redhat.com>

diff --git a/net/sunrpc/auth_gss/svcauth_gss.c b/net/sunrpc/auth_gss/svcauth_gss.c
index 224a82f24d3c..1095be9c80ab 100644
--- a/net/sunrpc/auth_gss/svcauth_gss.c
+++ b/net/sunrpc/auth_gss/svcauth_gss.c
@@ -463,6 +463,8 @@ static int rsc_parse(struct cache_detail *cd,
 		/* number of additional gid's */
 		if (get_int(&mesg, &N))
 			goto out;
+		if (N < 0 || N > NGROUPS_MAX)
+			goto out;
 		status = -ENOMEM;
 		rsci.cred.cr_group_info = groups_alloc(N);
 		if (rsci.cred.cr_group_info == NULL)