Re: [PATCH net] netfilter: nf_tables: fix pointer math issue in nft_byteorder_eval()

[Michal Kubecek]

On Fri, Nov 03, 2023 at 09:42:51AM +0300, Dan Carpenter wrote:
> The problem is in nft_byteorder_eval() where we are iterating through a
> loop and writing to dst[0], dst[1], dst[2] and so on...  On each
> iteration we are writing 8 bytes.  But dst[] is an array of u32 so each
> element only has space for 4 bytes.  That means that every iteration
> overwrites part of the previous element.
> 
> I spotted this bug while reviewing commit caf3ef7468f7 ("netfilter:
> nf_tables: prevent OOB access in nft_byteorder_eval") which is a related
> issue.  I think that the reason we have not detected this bug in testing
> is that most of time we only write one element.
> 
> Fixes: ce1e7989d989 ("netfilter: nft_byteorder: provide 64bit le/be conversion")
> Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> ---
>  include/net/netfilter/nf_tables.h | 4 ++--
>  net/netfilter/nft_byteorder.c     | 5 +++--
>  net/netfilter/nft_meta.c          | 2 +-
>  3 files changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/include/net/netfilter/nf_tables.h b/include/net/netfilter/nf_tables.h
> index 3bbd13ab1ecf..b157c5cafd14 100644
> --- a/include/net/netfilter/nf_tables.h
> +++ b/include/net/netfilter/nf_tables.h
> @@ -178,9 +178,9 @@ static inline __be32 nft_reg_load_be32(const u32 *sreg)
>  	return *(__force __be32 *)sreg;
>  }
>  
> -static inline void nft_reg_store64(u32 *dreg, u64 val)
> +static inline void nft_reg_store64(u64 *dreg, u64 val)
>  {
> -	put_unaligned(val, (u64 *)dreg);
> +	put_unaligned(val, dreg);
>  }
>  
>  static inline u64 nft_reg_load64(const u32 *sreg)
> diff --git a/net/netfilter/nft_byteorder.c b/net/netfilter/nft_byteorder.c
> index e596d1a842f7..f6e791a68101 100644
> --- a/net/netfilter/nft_byteorder.c
> +++ b/net/netfilter/nft_byteorder.c
> @@ -38,13 +38,14 @@ void nft_byteorder_eval(const struct nft_expr *expr,
>  
>  	switch (priv->size) {
>  	case 8: {
> +		u64 *dst64 = (void *)dst;
>  		u64 src64;
>  
>  		switch (priv->op) {
>  		case NFT_BYTEORDER_NTOH:
>  			for (i = 0; i < priv->len / 8; i++) {
>  				src64 = nft_reg_load64(&src[i]);
> -				nft_reg_store64(&dst[i],
> +				nft_reg_store64(&dst64[i],
>  						be64_to_cpu((__force __be64)src64));
>  			}
>  			break;
> @@ -52,7 +53,7 @@ void nft_byteorder_eval(const struct nft_expr *expr,
>  			for (i = 0; i < priv->len / 8; i++) {
>  				src64 = (__force __u64)
>  					cpu_to_be64(nft_reg_load64(&src[i]));
> -				nft_reg_store64(&dst[i], src64);
> +				nft_reg_store64(&dst64[i], src64);
>  			}
>  			break;
>  		}

I stumbled upon this when the issue got a CVE id (sigh) and I share
Andrea's (Cc-ed) concern that the fix is incomplete. While the fix,
commit c301f0981fdd ("netfilter: nf_tables: fix pointer math issue in
nft_byteorder_eval()") now, fixes the destination side, src is still
a pointer to u32, i.e. we are reading 64-bit values with relative
offsets which are multiples of 32 bits.

Shouldn't we fix this as well, e.g. like indicated below?

Michal

------------------------------------------------------------------------------
diff --git a/include/net/netfilter/nf_tables.h b/include/net/netfilter/nf_tables.h
index 001226c34621..bb4b83ea2908 100644
--- a/include/net/netfilter/nf_tables.h
+++ b/include/net/netfilter/nf_tables.h
@@ -183,9 +183,9 @@ static inline void nft_reg_store64(u64 *dreg, u64 val)
 	put_unaligned(val, dreg);
 }
 
-static inline u64 nft_reg_load64(const u32 *sreg)
+static inline u64 nft_reg_load64(const u64 *sreg)
 {
-	return get_unaligned((u64 *)sreg);
+	return get_unaligned(sreg);
 }
 
 static inline void nft_data_copy(u32 *dst, const struct nft_data *src,
diff --git a/net/netfilter/nft_byteorder.c b/net/netfilter/nft_byteorder.c
index f6e791a68101..2a64c69ed507 100644
--- a/net/netfilter/nft_byteorder.c
+++ b/net/netfilter/nft_byteorder.c
@@ -39,21 +39,22 @@ void nft_byteorder_eval(const struct nft_expr *expr,
 	switch (priv->size) {
 	case 8: {
 		u64 *dst64 = (void *)dst;
-		u64 src64;
+		u64 *src64 = (void *)src;
+		u64 val64;
 
 		switch (priv->op) {
 		case NFT_BYTEORDER_NTOH:
 			for (i = 0; i < priv->len / 8; i++) {
-				src64 = nft_reg_load64(&src[i]);
+				val64 = nft_reg_load64(&src64[i]);
 				nft_reg_store64(&dst64[i],
-						be64_to_cpu((__force __be64)src64));
+						be64_to_cpu((__force __be64)val64));
 			}
 			break;
 		case NFT_BYTEORDER_HTON:
 			for (i = 0; i < priv->len / 8; i++) {
-				src64 = (__force __u64)
-					cpu_to_be64(nft_reg_load64(&src[i]));
-				nft_reg_store64(&dst64[i], src64);
+				val64 = (__force __u64)
+					cpu_to_be64(nft_reg_load64(&src64[i]));
+				nft_reg_store64(&dst64[i], val64);
 			}
 			break;
 		}
------------------------------------------------------------------------------

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