Re: [PATCH] powerpc/papr_scm: Fix an off-by-one check in papr_scm_meta_{get, set}

From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To: Vaibhav Jain <vaibhav@linux.ibm.com>, linuxppc-dev@lists.ozlabs.org
Cc: Vaibhav Jain <vaibhav@linux.ibm.com>,
	Oliver O'Halloran <oohall@gmail.com>
Subject: Re: [PATCH] powerpc/papr_scm: Fix an off-by-one check in papr_scm_meta_{get, set}
Date: Sat, 28 Sep 2019 21:30:42 +0530	[thread overview]
Message-ID: <87zhiocswl.fsf@linux.ibm.com> (raw)
In-Reply-To: <20190927062002.3169-1-vaibhav@linux.ibm.com>

Vaibhav Jain <vaibhav@linux.ibm.com> writes:

> A validation check to prevent out of bounds read/write inside
> functions papr_scm_meta_{get,set}() is off-by-one that prevent reads
> and writes to the last byte of the label area.
>
> This bug manifests as a failure to probe a dimm when libnvdimm is
> unable to read the entire config-area as advertised by
> ND_CMD_GET_CONFIG_SIZE. This usually happens when there are large
> number of namespaces created in the region backed by the dimm and the
> label-index spans max possible config-area. An error of the form below
> usually reported in the kernel logs:
>
> [  255.293912] nvdimm: probe of nmem0 failed with error -22
>
> The patch fixes these validation checks there by letting libnvdimm
> access the entire config-area.
>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>

> Fixes: 53e80bd042773('powerpc/nvdimm: Add support for multibyte read/write for metadata')
> Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
> ---
>  arch/powerpc/platforms/pseries/papr_scm.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
> index a5ac371a3f06..0d0f4974a301 100644
> --- a/arch/powerpc/platforms/pseries/papr_scm.c
> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
> @@ -124,7 +124,7 @@ static int papr_scm_meta_get(struct papr_scm_priv *p,
>  	int len, read;
>  	int64_t ret;
>  
> -	if ((hdr->in_offset + hdr->in_length) >= p->metadata_size)
> +	if ((hdr->in_offset + hdr->in_length) > p->metadata_size)
>  		return -EINVAL;
>  
>  	for (len = hdr->in_length; len; len -= read) {
> @@ -178,7 +178,7 @@ static int papr_scm_meta_set(struct papr_scm_priv *p,
>  	__be64 data_be;
>  	int64_t ret;
>  
> -	if ((hdr->in_offset + hdr->in_length) >= p->metadata_size)
> +	if ((hdr->in_offset + hdr->in_length) > p->metadata_size)
>  		return -EINVAL;
>  
>  	for (len = hdr->in_length; len; len -= wrote) {
> -- 
> 2.21.0