On Wed, Apr 20, 2011 at 01:09:35PM +0100, Sachin Prabhu wrote:
> An open on a NFS4 share using the O_CREAT flag on an existing file for
> which we have permissions to open but contained in a directory with no
> write permissions will fail with EACCES.
>
> A tcpdump shows that the client had set the open mode to UNCHECKED which
> indicates that the file should be created if it doesn't exist and
> encountering an existing flag is not an error. Since in this case the
> file exists and can be opened by the user, the NFS server is wrong in
> attempting to check create permissions on the parent directory.
>
> The patch adds a conditional statement to check for create permissions
> only if the file doesn't exist.
That looks correct to me, thanks.
It's a bad bug, but appears to be one we've lived with a long time, so
I'm a bit up in the air whether to submit now for 2.6.39 or to queue up
for 2.6.40.
--b.
>
> Signed-off-by: Sachin S. Prabhu <sprabhu@xxxxxxxxxx>
>
> diff -up linux-2.6/fs/nfsd/vfs.c.bz683372 linux-2.6/fs/nfsd/vfs.c
> --- linux-2.6/fs/nfsd/vfs.c.bz683372 2011-04-20 13:03:54.021040329 +0100
> +++ linux-2.6/fs/nfsd/vfs.c 2011-04-20 13:05:21.551858218 +0100
> @@ -1363,7 +1363,7 @@ nfsd_create_v3(struct svc_rqst *rqstp, s
> goto out;
> if (!(iap->ia_valid & ATTR_MODE))
> iap->ia_mode = 0;
> - err = fh_verify(rqstp, fhp, S_IFDIR, NFSD_MAY_CREATE);
> + err = fh_verify(rqstp, fhp, S_IFDIR, NFSD_MAY_EXEC);
> if (err)
> goto out;
>
> @@ -1385,6 +1385,13 @@ nfsd_create_v3(struct svc_rqst *rqstp, s
> if (IS_ERR(dchild))
> goto out_nfserr;
>
> + /* If file doesn't exist, check for permissions to create one */
> + if (!dchild->d_inode) {
> + err = fh_verify(rqstp, fhp, S_IFDIR, NFSD_MAY_CREATE);
> + if (err)
> + goto out;
> + }
> +
> err = fh_compose(resfhp, fhp->fh_export, dchild, fhp);
> if (err)
> goto out;
>
>
> --
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