evaluate: make sure chain jump name comes with a null byte

There is a stack oob read access in netlink_gen_chain():

	mpz_export_data(chain, expr->chain->value,
			BYTEORDER_HOST_ENDIAN, len);
	snprintf(data->chain, NFT_CHAIN_MAXNAMELEN, "%s", chain);

There is no guarantee that chain[] is null terminated, so snprintf
can read past chain[] array.  ASAN report is:

AddressSanitizer: stack-buffer-overflow on address 0x7ffff5f00520 at ..
READ of size 257 at 0x7ffff5f00520 thread T0
    #0 0x00000032ffb6 in printf_common(void*, char const*, __va_list_tag*) (src/nft+0x32ffb6)
    #1 0x00000033055d in vsnprintf (src/nft+0x33055d)
    #2 0x000000332071 in snprintf (src/nft+0x332071)
    #3 0x0000004eef03 in netlink_gen_chain src/netlink.c:454:2
    #4 0x0000004eef03 in netlink_gen_verdict src/netlink.c:467:4

Reject chain jumps that exceed 255 characters, which matches the netlink
policy on the kernel side.

The included reproducer fails without asan too because the kernel will
reject the too-long chain name. But that happens after the asan detected
bogus read.

Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/src/evaluate.c b/src/evaluate.c
index 783a373b6268a871210dc22275606839a706894d..ab50cb0aadf64c98ac890c12d2c12489cb1a07ae 100644 (file)
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -3040,16 +3040,32 @@ static int expr_evaluate_xfrm(struct eval_ctx *ctx, struct expr **exprp)
        return expr_evaluate_primary(ctx, exprp);
 }
 
-static int verdict_validate_chainlen(struct eval_ctx *ctx,
+static int verdict_validate_chain(struct eval_ctx *ctx,
                                     struct expr *chain)
 {
-       if (chain->len > NFT_CHAIN_MAXNAMELEN * BITS_PER_BYTE)
+       char buf[NFT_CHAIN_MAXNAMELEN];
+       unsigned int len;
+
+       len = chain->len / BITS_PER_BYTE;
+       if (len > NFT_CHAIN_MAXNAMELEN)
                return expr_error(ctx->msgs, chain,
                                  "chain name too long (%u, max %u)",
                                  chain->len / BITS_PER_BYTE,
                                  NFT_CHAIN_MAXNAMELEN);
 
-       return 0;
+       if (!len)
+               return expr_error(ctx->msgs, chain,
+                                 "chain name length 0 not allowed");
+
+       memset(buf, 0, sizeof(buf));
+       mpz_export_data(buf, chain->value, BYTEORDER_HOST_ENDIAN, len);
+
+       if (strnlen(buf, sizeof(buf)) < sizeof(buf))
+               return 0;
+
+       return expr_error(ctx->msgs, chain,
+                         "chain name must be smaller than %u",
+                         NFT_CHAIN_MAXNAMELEN);
 }
 
 static int expr_evaluate_verdict(struct eval_ctx *ctx, struct expr **exprp)
@@ -3060,7 +3076,7 @@ static int expr_evaluate_verdict(struct eval_ctx *ctx, struct expr **exprp)
        case NFT_GOTO:
        case NFT_JUMP:
                if (expr->chain->etype == EXPR_VALUE &&
-                   verdict_validate_chainlen(ctx, expr->chain))
+                   verdict_validate_chain(ctx, expr->chain))
                        return -1;
 
                break;
@@ -3296,7 +3312,7 @@ static int stmt_evaluate_verdict(struct eval_ctx *ctx, struct stmt *stmt)
                                                  "not a value expression");
                        }
 
-                       if (verdict_validate_chainlen(ctx, stmt->expr->chain))
+                       if (verdict_validate_chain(ctx, stmt->expr->chain))
                                return -1;
                }
                break;

diff --git a/tests/shell/testcases/bogons/nft-f/asan_out_of_bounds_read_with_long_chain b/tests/shell/testcases/bogons/nft-f/asan_out_of_bounds_read_with_long_chain
new file mode 100644 (file)
index 0000000..e166a03
--- /dev/null
+++ b/tests/shell/testcases/bogons/nft-f/asan_out_of_bounds_read_with_long_chain
@@ -0,0 +1,3 @@
+add table t
+add chain t eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
+add rule  t eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee jump   eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee