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SubjectRe: [PATCH] NFS: nfsaclsvc_encode_getaclres() - Fix potential NULL deref and tiny optimization.
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On Friday 27 October 2006 23:46, David Rientjes wrote:
> On Fri, 27 Oct 2006, Jesper Juhl wrote:
>
> > In fs/nfsd/nfs2acl.c::nfsaclsvc_encode_getaclres() I see a few issues.
> >
> > 1) At the top of the function we assign to the 'inode' variable by
> > dereferencing 'dentry', but further down we test 'dentry' for NULL. So, if
> > 'dentry' (which is really 'resp->fh.fh_dentry') can be NULL, then either
> > we have a potential NULL pointer deref bug or we have a superflous test.
> >
>
> resp->fh.fh_dentry cannot be NULL on nfsaclsvc_encode_getaclres so the
> early assignment is appropriate for both *dentry and *inode.

I didn't convince myself of that on my first scan of the code, that's why
I opted to keep the NULL check.

> *inode will
> need to be checked for NULL in the conditional, however, and return 0 on
> true.
>
Right, that agrees with my reading as well.

> > 3) There are two locations in the function where we may return before we
> > use the value of the variable 'w', but we compute it at the very top of the
> > function. So in the case where we return early we have wasted a few cycles
> > computing a value that was never used.
> >
>
> w should be an unsigned int.
>
Makes sense.

Thank you for commenting.

Here's a patch, on top of the previous one, to address you comments.
Feedback welcome.

Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
---

fs/nfsd/nfs2acl.c | 7 +++----
1 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/fs/nfsd/nfs2acl.c b/fs/nfsd/nfs2acl.c
index d89d63f..069d7d0 100644
--- a/fs/nfsd/nfs2acl.c
+++ b/fs/nfsd/nfs2acl.c
@@ -222,14 +222,13 @@ static int nfsaclsvc_encode_getaclres(st
{
struct dentry *dentry = resp->fh.fh_dentry;
struct kvec *head = rqstp->rq_res.head;
- struct inode *inode;
+ struct inode *inode = dentry->d_inode;
unsigned int base;
- int w;
+ unsigned int w;
int n;

- if (dentry == NULL || dentry->d_inode == NULL)
+ if (!inode)
return 0;
- inode = dentry->d_inode;

p = nfs2svc_encode_fattr(rqstp, p, &resp->fh);
*p++ = htonl(resp->mask);
-
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