> On Feb 9, 2017, at 9:22 AM, Christoph Hellwig <hch@xxxxxx> wrote:
>
> The switch to vfs_truncate in nfsd_setattr dropped the owner override
> used for NFS permissions. Add a copy of vfs_truncate with it restored
> to the nfsd code for now as it's very late in the cycle, but there
> should be a way to consolidate it back in the future.
>
> Fixes: 41f53350 ("nfsd: special case truncates some more")
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> Reported-by: Chuck Lever <chucklever@xxxxxxxxx>
> ---
> fs/nfsd/vfs.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 80 insertions(+), 1 deletion(-)
>
> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index a974368026a1..fd4a32e0b0b4 100644
> --- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -332,6 +332,85 @@ nfsd_sanitize_attrs(struct inode *inode, struct iattr *iap)
> }
> }
>
> +/* copy of vfs_truncate with NFS owner override hacked in, sigh.. */
> +static long nfsd_truncate(const struct path *path, loff_t length)
> +{
> + struct inode *inode;
> + struct dentry *upperdentry;
> + long error;
> +
> + inode = path->dentry->d_inode;
> +
> + /* For directories it's -EISDIR, for other non-regulars - -EINVAL */
> + if (S_ISDIR(inode->i_mode))
> + return -EISDIR;
> + if (!S_ISREG(inode->i_mode))
> + return -EINVAL;
> +
> + error = mnt_want_write(path->mnt);
> + if (error)
> + goto out;
> +
> + /*
> + * The file owner always gets access permission for accesses that
> + * would normally be checked at open time. This is to make
> + * file access work even when the client has done a fchmod(fd, 0).
> + *
> + * However, `cp foo bar' should fail nevertheless when bar is
> + * readonly. A sensible way to do this might be to reject all
> + * attempts to truncate a read-only file, because a creat() call
> + * always implies file truncation.
> + * ... but this isn't really fair. A process may reasonably call
> + * ftruncate on an open file descriptor on a file with perm 000.
> + * We must trust the client to do permission checking - using "ACCESS"
> + * with NFSv3.
> + */
> + if (!uid_eq(inode->i_uid, current_fsuid())) {
> + error = inode_permission(inode, MAY_WRITE);
> + if (error)
> + goto mnt_drop_write_and_out;
> + }
> +
> + error = -EPERM;
> + if (IS_APPEND(inode))
> + goto mnt_drop_write_and_out;
> +
> + /*
> + * If this is an overlayfs then do as if opening the file so we get
> + * write access on the upper inode, not on the overlay inode. For
> + * non-overlay filesystems d_real() is an identity function.
> + */
> + upperdentry = d_real(path->dentry, NULL, O_WRONLY);
> + error = PTR_ERR(upperdentry);
> + if (IS_ERR(upperdentry))
> + goto mnt_drop_write_and_out;
> +
> + error = get_write_access(upperdentry->d_inode);
> + if (error)
> + goto mnt_drop_write_and_out;
> +
> + /*
> + * Make sure that there are no leases. get_write_access() protects
> + * against the truncate racing with a lease-granting setlease().
> + */
> + error = break_lease(inode, O_WRONLY);
> + if (error)
> + goto put_write_and_out;
> +
> + error = locks_verify_truncate(inode, NULL, length);
> + if (!error)
> + error = security_path_truncate(path);
> + if (!error)
> + error = do_truncate(path->dentry, length, 0, NULL);
do_truncate does not seem to be available in the EXPORT_SYMBOL pool.
> +
> +put_write_and_out:
> + put_write_access(upperdentry->d_inode);
> +mnt_drop_write_and_out:
> + mnt_drop_write(path->mnt);
> +out:
> + return error;
> +}
> +
> /*
> * Set various file attributes. After this call fhp needs an fh_put.
> */
> @@ -398,7 +477,7 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp, struct iattr *iap,
> ((iap->ia_valid & ~(ATTR_SIZE | ATTR_MTIME)) == 0))
> implicit_mtime = true;
>
> - host_err = vfs_truncate(&path, iap->ia_size);
> + host_err = nfsd_truncate(&path, iap->ia_size);
> if (host_err)
> goto out_host_err;
>
> --
> 2.11.0
>
> --
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--
Chuck Lever
chucklever@xxxxxxxxx
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