Re: [PATCH] fs/9p/xattr.c: catch the error of p9_client_clunk when setting xattr failed

Dominique Martinet
2018-07-25T03:32:20Z

piaojun wrote on Wed, Jul 25, 2018:
> In my testing, v9fs_fid_xattr_set will return successfully even if the
> backend ext4 filesystem has no space to store xattr key-value. That will
> cause inconsistent behavior between front end and back end. The reason is
> that lsetxattr will be triggered by p9_client_clunk, and unfortunately we
> did not catch the error. This patch will catch the error to notify upper
> caller.
>
> p9_client_clunk (in 9p)
> p9_client_rpc(clnt, P9_TCLUNK, "d", fid->fid);
> v9fs_clunk (in qemu)
> put_fid
> free_fid
> v9fs_xattr_fid_clunk
> v9fs_co_lsetxattr
> s->ops->lsetxattr
> ext4_xattr_user_set (in host ext4 filesystem)
>
> Signed-off-by: Jun Piao <piaojun@huawei.com>

Good catch!

LGTM on its own but see comment below for further error checking.
Please let me know if you want to do this in a v2 or submit a separate
patch altogether, I can pick this one up as it is.

> ---
> fs/9p/xattr.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/fs/9p/xattr.c b/fs/9p/xattr.c
> index f329eee..352abc3 100644
> --- a/fs/9p/xattr.c
> +++ b/fs/9p/xattr.c
> @@ -105,7 +105,7 @@ int v9fs_fid_xattr_set(struct p9_fid *fid, const char *name,
> {
> struct kvec kvec = {.iov_base = (void *)value, .iov_len = value_len};
> struct iov_iter from;
> - int retval;
> + int retval, err;
>
> iov_iter_kvec(&from, WRITE | ITER_KVEC, &kvec, 1, value_len);
>
> @@ -126,7 +126,9 @@ int v9fs_fid_xattr_set(struct p9_fid *fid, const char *name,
> retval);
> else
> p9_client_write(fid, 0, &from, &retval);

I'm not sure what to do about this but it's also possible for
p9_client_write to not write the full length without setting and error.

We should probably compare the return value of p9_client_write and
value_len to detect short writes and return an error in this case.

> - p9_client_clunk(fid);
> + err = p9_client_clunk(fid);
> + if (!retval && err)
> + retval = err;
> return retval;
> }
>
> --