netfilter: nft_byteorder: remove multi-register support

64bit byteorder conversion is broken when several registers need to be
converted because the source register array advances in steps for 4 bytes
instead of 8:

  for (i = ...
      src64 = nft_reg_load64(&src[i]);
                             ~~~~~ u32 *src
      nft_reg_store64(&dst64[i],

Remove the multi-register support, it has other issues as well:

Pablo points out that commit
caf3ef7468f7 ("netfilter: nf_tables: prevent OOB access in nft_byteorder_eval")
alters semantics: before the loop operated on registers, i.e.
 for ( ... )
   dst32[i] = htons((u16)src32[i])

 .. but after the patch it will operate on bytes, which makes this
 useless to convert e.g. concatenations, which store each compound
 in its own register.

Multi-convert of u32 has one theoretical application:

ct mark . meta mark . tcp dport @intervalset

Because ct mark and meta mark are host byte order, use with
intervals has to convert the byteorder for ct/meta mark value
to network byte order (bigendian).

nftables emits this:
 [ meta load mark => reg 1 ]
 [ byteorder reg 1 = hton(reg 1, 4, 4) ]
 [ ct load mark => reg 9 ]
 [ byteorder reg 9 = hton(reg 9, 4, 4) ]
 ...

I.e. two separate calls.  Theoretically it could be changed to do:
 [ meta load mark => reg 1 ]
 [ ct load mark => reg 9 ]
 [ byteorder reg 1 = htonl(reg 1, 4, 8) ]
 ...

But then all it would take to change the set to
meta mark . tcp dport . ct mark

... and we'd be back to two "byteorder" calls. IOW, support to
convert a range of registers is both dysfunctional and dubious.

Simplify this: remove the feature.

Pablo Neira Ayuso points out that nftables before 1.1.0 can generate
incorrect byteorder conversions, see 9fe58952c45a,
"evaluate: skip byteorder conversion for selector smaller than 2 bytes"
in nftables.git).  Affected rulesets fail to load with this change and
old userspace due to 'len != size' check.

Fixes: c301f0981fdd ("netfilter: nf_tables: fix pointer math issue in nft_byteorder_eval()")
Cc: <stable+noautosel@kernel.org> # may break rule load with old nftables versions
Reported-by: Michal Kubecek <mkubecek@suse.cz>
Link: https://lore.kernel.org/netfilter-devel/20240206104336.ctigqpkunom2ufmn@lion.mk-sys.cz/
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/nft_byteorder.c b/net/netfilter/nft_byteorder.c
index 2316c77f422803063fd0dfb0bb1b83c0b8798805..dfd41fc8d9b8f7f1c752d95ab4b1089b01de99ac 100644 (file)
--- a/net/netfilter/nft_byteorder.c
+++ b/net/netfilter/nft_byteorder.c
@@ -19,7 +19,6 @@ struct nft_byteorder {
        u8                      sreg;
        u8                      dreg;
        enum nft_byteorder_ops  op:8;
-       u8                      len;
        u8                      size;
 };
 
@@ -28,13 +27,8 @@ void nft_byteorder_eval(const struct nft_expr *expr,
                        const struct nft_pktinfo *pkt)
 {
        const struct nft_byteorder *priv = nft_expr_priv(expr);
-       u32 *src = &regs->data[priv->sreg];
+       const u32 *src = &regs->data[priv->sreg];
        u32 *dst = &regs->data[priv->dreg];
-       u16 *s16, *d16;
-       unsigned int i;
-
-       s16 = (void *)src;
-       d16 = (void *)dst;
 
        switch (priv->size) {
        case 8: {
@@ -43,18 +37,14 @@ void nft_byteorder_eval(const struct nft_expr *expr,
 
                switch (priv->op) {
                case NFT_BYTEORDER_NTOH:
-                       for (i = 0; i < priv->len / 8; i++) {
-                               src64 = nft_reg_load64(&src[i]);
-                               nft_reg_store64(&dst64[i],
-                                               be64_to_cpu((__force __be64)src64));
-                       }
+                       src64 = nft_reg_load64(src);
+
+                       nft_reg_store64(dst64, be64_to_cpu((__force __be64)src64));
                        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);
-                       }
+                       src64 = (__force __u64)cpu_to_be64(nft_reg_load64(src));
+
+                       nft_reg_store64(dst64, src64);
                        break;
                }
                break;
@@ -62,24 +52,20 @@ void nft_byteorder_eval(const struct nft_expr *expr,
        case 4:
                switch (priv->op) {
                case NFT_BYTEORDER_NTOH:
-                       for (i = 0; i < priv->len / 4; i++)
-                               dst[i] = ntohl((__force __be32)src[i]);
+                       *dst = ntohl((__force __be32)*src);
                        break;
                case NFT_BYTEORDER_HTON:
-                       for (i = 0; i < priv->len / 4; i++)
-                               dst[i] = (__force __u32)htonl(src[i]);
+                       *dst = (__force __u32)htonl(*src);
                        break;
                }
                break;
        case 2:
                switch (priv->op) {
                case NFT_BYTEORDER_NTOH:
-                       for (i = 0; i < priv->len / 2; i++)
-                               d16[i] = ntohs((__force __be16)s16[i]);
+                       nft_reg_store16(dst, ntohs(nft_reg_load_be16(src)));
                        break;
                case NFT_BYTEORDER_HTON:
-                       for (i = 0; i < priv->len / 2; i++)
-                               d16[i] = (__force __u16)htons(s16[i]);
+                       nft_reg_store_be16(dst, htons(nft_reg_load16(src)));
                        break;
                }
                break;
@@ -137,20 +123,22 @@ static int nft_byteorder_init(const struct nft_ctx *ctx,
        if (err < 0)
                return err;
 
-       priv->len = len;
+       /* no longer support multi-reg conversions */
+       if (len != size)
+               return -EOPNOTSUPP;
 
        err = nft_parse_register_load(ctx, tb[NFTA_BYTEORDER_SREG], &priv->sreg,
-                                     priv->len);
+                                     len);
        if (err < 0)
                return err;
 
        err = nft_parse_register_store(ctx, tb[NFTA_BYTEORDER_DREG],
                                       &priv->dreg, NULL, NFT_DATA_VALUE,
-                                      priv->len);
+                                      len);
        if (err < 0)
                return err;
 
-       if (nft_reg_overlap(priv->sreg, priv->dreg, priv->len))
+       if (nft_reg_overlap(priv->sreg, priv->dreg, len))
                return -EINVAL;
 
        return 0;
@@ -167,10 +155,11 @@ static int nft_byteorder_dump(struct sk_buff *skb,
                goto nla_put_failure;
        if (nla_put_be32(skb, NFTA_BYTEORDER_OP, htonl(priv->op)))
                goto nla_put_failure;
-       if (nla_put_be32(skb, NFTA_BYTEORDER_LEN, htonl(priv->len)))
-               goto nla_put_failure;
        if (nla_put_be32(skb, NFTA_BYTEORDER_SIZE, htonl(priv->size)))
                goto nla_put_failure;
+       /* compatibility for old userspace which permitted size != len */
+       if (nla_put_be32(skb, NFTA_BYTEORDER_LEN, htonl(priv->size)))
+               goto nla_put_failure;
        return 0;
 
 nla_put_failure: