Re: [PATCH] nfsd: fix memory corruption caused by readdir

[J. Bruce Fields]

On Mon, Mar 04, 2019 at 02:08:22PM +1100, NeilBrown wrote:
> (Note that the commit hash in the Fixes tag is from the 'history'
>  tree - this bug predates git).
> Fixes: eb229d253e6c ("[PATCH] kNFSd: fix two xdr-encode bugs for readdirplus reply")

It'd be nice to provide a URL for that.  The one I originally cloned one
seems to have disappeared.

> Cc: stable@xxxxxxxxxxxxxxx (v2.6.12+)
> Signed-off-by: NeilBrown <neilb@xxxxxxxx>
> ---
> 
> Can I still get extra credit for fixing a bug that is 14.5 years old, if
> I'm the one who introduced it?

Good grief, yes!  Great fix.  Is that a record?

And how did it go undetected so long, and what caused it to surface just
now?

I once thought about converting this over to the xdr_stream api that
NFSv4 uses to hide the page-crossing logic now.  But I think it's better
to leave it alone.

--b.

> 
>  fs/nfsd/nfs3proc.c | 16 ++++++++++++++--
>  fs/nfsd/nfs3xdr.c  |  1 +
>  2 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
> index 9eb8086ea841..c9cf46e0c040 100644
> --- a/fs/nfsd/nfs3proc.c
> +++ b/fs/nfsd/nfs3proc.c
> @@ -463,8 +463,19 @@ nfsd3_proc_readdir(struct svc_rqst *rqstp)
>  					&resp->common, nfs3svc_encode_entry);
>  	memcpy(resp->verf, argp->verf, 8);
>  	resp->count = resp->buffer - argp->buffer;
> -	if (resp->offset)
> -		xdr_encode_hyper(resp->offset, argp->cookie);
> +	if (resp->offset) {
> +		loff_t offset = argp->cookie;
> +
> +		if (unlikely(resp->offset1)) {
> +			/* we ended up with offset on a page boundary */
> +			*resp->offset = htonl(offset >> 32);
> +			*resp->offset1 = htonl(offset & 0xffffffff);
> +			resp->offset1 = NULL;
> +		} else {
> +			xdr_encode_hyper(resp->offset, offset);
> +		}
> +		resp->offset = NULL;
> +	}
>  
>  	RETURN_STATUS(nfserr);
>  }
> @@ -533,6 +544,7 @@ nfsd3_proc_readdirplus(struct svc_rqst *rqstp)
>  		} else {
>  			xdr_encode_hyper(resp->offset, offset);
>  		}
> +		resp->offset = NULL;
>  	}
>  
>  	RETURN_STATUS(nfserr);
> diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c
> index 9b973f4f7d01..83919116d5cb 100644
> --- a/fs/nfsd/nfs3xdr.c
> +++ b/fs/nfsd/nfs3xdr.c
> @@ -921,6 +921,7 @@ encode_entry(struct readdir_cd *ccd, const char *name, int namlen,
>  		} else {
>  			xdr_encode_hyper(cd->offset, offset64);
>  		}
> +		cd->offset = NULL;
>  	}
>  
>  	/*
> -- 
> 2.14.0.rc0.dirty
>