summaryrefslogtreecommitdiffstats
path: root/net
diff options
context:
space:
mode:
authorSergey Marinkevich <sergey.marinkevich@eltex-co.ru>2020-03-29 19:19:14 +0700
committerPablo Neira Ayuso <pablo@netfilter.org>2020-03-30 21:17:53 +0200
commit2e34328b396a69b73661ba38d47d92b7cf21c2c4 (patch)
treea18e0ecd48b6a08466b3f03fd73f8bc1963b02ce /net
parentef803b3cf96a26e2a601755b237585a23e6bc30c (diff)
downloadlinux-2e34328b396a69b73661ba38d47d92b7cf21c2c4.tar.bz2
netfilter: nft_exthdr: fix endianness of tcp option cast
I got a problem on MIPS with Big-Endian is turned on: every time when NF trying to change TCP MSS it returns because of new.v16 was greater than old.v16. But real MSS was 1460 and my rule was like this: add rule table chain tcp option maxseg size set 1400 And 1400 is lesser that 1460, not greater. Later I founded that main causer is cast from u32 to __be16. Debugging: In example MSS = 1400(HEX: 0x578). Here is representation of each byte like it is in memory by addresses from left to right(e.g. [0x0 0x1 0x2 0x3]). LE — Little-Endian system, BE — Big-Endian, left column is type. LE BE u32: [78 05 00 00] [00 00 05 78] As you can see, u32 representation will be casted to u16 from different half of 4-byte address range. But actually nf_tables uses registers and store data of various size. Actually TCP MSS stored in 2 bytes. But registers are still u32 in definition: struct nft_regs { union { u32 data[20]; struct nft_verdict verdict; }; }; So, access like regs->data[priv->sreg] exactly u32. So, according to table presents above, per-byte representation of stored TCP MSS in register will be: LE BE (u32)regs->data[]: [78 05 00 00] [05 78 00 00] ^^ ^^ We see that register uses just half of u32 and other 2 bytes may be used for some another data. But in nft_exthdr_tcp_set_eval() it casted just like u32 -> __be16: new.v16 = src But u32 overfill __be16, so it get 2 low bytes. For clarity draw one more table(<xx xx> means that bytes will be used for cast). LE BE u32: [<78 05> 00 00] [00 00 <05 78>] (u32)regs->data[]: [<78 05> 00 00] [05 78 <00 00>] As you can see, for Little-Endian nothing changes, but for Big-endian we take the wrong half. In my case there is some other data instead of zeros, so new MSS was wrongly greater. For shooting this bug I used solution for ports ranges. Applying of this patch does not affect Little-Endian systems. Signed-off-by: Sergey Marinkevich <sergey.marinkevich@eltex-co.ru> Acked-by: Florian Westphal <fw@strlen.de> Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Diffstat (limited to 'net')
-rw-r--r--net/netfilter/nft_exthdr.c8
1 files changed, 3 insertions, 5 deletions
diff --git a/net/netfilter/nft_exthdr.c b/net/netfilter/nft_exthdr.c
index a5e8469859e3..07782836fad6 100644
--- a/net/netfilter/nft_exthdr.c
+++ b/net/netfilter/nft_exthdr.c
@@ -228,7 +228,6 @@ static void nft_exthdr_tcp_set_eval(const struct nft_expr *expr,
unsigned int i, optl, tcphdr_len, offset;
struct tcphdr *tcph;
u8 *opt;
- u32 src;
tcph = nft_tcp_header_pointer(pkt, sizeof(buff), buff, &tcphdr_len);
if (!tcph)
@@ -237,7 +236,6 @@ static void nft_exthdr_tcp_set_eval(const struct nft_expr *expr,
opt = (u8 *)tcph;
for (i = sizeof(*tcph); i < tcphdr_len - 1; i += optl) {
union {
- u8 octet;
__be16 v16;
__be32 v32;
} old, new;
@@ -259,13 +257,13 @@ static void nft_exthdr_tcp_set_eval(const struct nft_expr *expr,
if (!tcph)
return;
- src = regs->data[priv->sreg];
offset = i + priv->offset;
switch (priv->len) {
case 2:
old.v16 = get_unaligned((u16 *)(opt + offset));
- new.v16 = src;
+ new.v16 = (__force __be16)nft_reg_load16(
+ &regs->data[priv->sreg]);
switch (priv->type) {
case TCPOPT_MSS:
@@ -283,7 +281,7 @@ static void nft_exthdr_tcp_set_eval(const struct nft_expr *expr,
old.v16, new.v16, false);
break;
case 4:
- new.v32 = src;
+ new.v32 = regs->data[priv->sreg];
old.v32 = get_unaligned((u32 *)(opt + offset));
if (old.v32 == new.v32)