Re: [PATCH] nfsd: make a copy of struct iattr before calling notify_change

[NeilBrown]

On Thu, 18 May 2023, Jeff Layton wrote:
> notify_change can modify the iattr structure. In particular it can can
> end up setting ATTR_MODE when ATTR_KILL_SUID is already set, causing a
> BUG() if the same iattr is passed to notify_change more than once.
> 
> Make a copy of the struct iattr before calling notify_change.
> 
> Fixes: 34b91dda7124 NFSD: Make nfsd4_setattr() wait before returning NFS4ERR_DELAY
> Link: https://bugzilla.redhat.com/show_bug.cgi?id=2207969
> Reported-by: Zhi Li <yieli@xxxxxxxxxx>
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
>  fs/nfsd/vfs.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index c4ef24c5ffd0..ad0c5cd900b1 100644
> --- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -538,7 +538,9 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp,
>  
>  	inode_lock(inode);
>  	for (retries = 1;;) {
> -		host_err = __nfsd_setattr(dentry, iap);
> +		struct iattr attrs = *iap;
> +
> +		host_err = __nfsd_setattr(dentry, &attrs);

I think this needs something to ensure a well meaning by-passer doesn't
try to "optimise" it back to the way it was.
Maybe make "iap" const?  Or add a comment?  Or both?

NeilBrown


>  		if (host_err != -EAGAIN || !retries--)
>  			break;
>  		if (!nfsd_wait_for_delegreturn(rqstp, inode))
> -- 
> 2.40.1
> 
>