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SubjectRe: [PATCH] nfsd: avoid out of bounds read on array nfsd4_layout_ops
On Tue, May 09, 2017 at 05:04:14PM +0300, Dan Carpenter wrote:
> On Tue, May 09, 2017 at 02:31:21PM +0100, Colin King wrote:
> > diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> > index 1dbf62190bee..c453a1998e00 100644
> > --- a/fs/nfsd/nfs4proc.c
> > +++ b/fs/nfsd/nfs4proc.c
> > @@ -1259,7 +1259,8 @@ nfsd4_layout_verify(struct svc_export *exp, unsigned int layout_type)
> > return NULL;
> > }
> >
> > - if (layout_type >= 32 || !(exp->ex_layout_types & (1 << layout_type))) {
> > + if (layout_type >= LAYOUT_TYPE_MAX ||
> > + !(exp->ex_layout_types & (1 << layout_type))) {
>
> The 32 is there to prevent a shift wrapping bug. The bit test prevents
> a buffer overflow so this can't actually overflow.

Yes, looks like a false positive for coverity.

> But this change doesn't hurt and is probably cleaner.

Sure. Hope it's OK if I just merge this into the previous commit:

--b.

commit 16b6f81d8ed9
Author: Ari Kauppi <ari@synopsys.com>
Date: Fri May 5 16:07:55 2017 -0400

nfsd: fix undefined behavior in nfsd4_layout_verify

UBSAN: Undefined behaviour in fs/nfsd/nfs4proc.c:1262:34
shift exponent 128 is too large for 32-bit type 'int'

Depending on compiler+architecture, this may cause the check for
layout_type to succeed for overly large values (which seems to be the
case with amd64). The large value will be later used in de-referencing
nfsd4_layout_ops for function pointers.

Reported-by: Jani Tuovila <tuovila@synopsys.com>
Signed-off-by: Ari Kauppi <ari@synopsys.com>
[colin.king@canonical.com: use LAYOUT_TYPE_MAX instead of 32]
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index d86031b6ad79..c453a1998e00 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -1259,7 +1259,8 @@ nfsd4_layout_verify(struct svc_export *exp, unsigned int layout_type)
return NULL;
}

- if (!(exp->ex_layout_types & (1 << layout_type))) {
+ if (layout_type >= LAYOUT_TYPE_MAX ||
+ !(exp->ex_layout_types & (1 << layout_type))) {
dprintk("%s: layout type %d not supported\n",
__func__, layout_type);
return NULL;
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