[PATCH v2] netfilter: xt_hashlimit: fix build error caused by 64bit division

[PATCH v2] netfilter: xt_hashlimit: fix build error caused by 64bit division

[Vishwanath Pai]

64bit division causes build/link errors on 32bit architectures. It
prints out error messages like:

ERROR: "__aeabi_uldivmod" [net/netfilter/xt_hashlimit.ko] undefined!

The value of avg passed through by userspace in BYTE mode cannot exceed
U32_MAX. Which means 64bit division in user2rate_bytes is unnecessary.
To fix this I have changed the type of param 'user' to u32.

Since anything greater than U32_MAX is an invalid input we error out in
hashlimit_mt_check_common() when this is the case.

Changes in v2:
	Making return type as u32 would cause an overflow for small
	values of 'user' (for example 2, 3 etc). To avoid this I bumped up
	'r' to u64 again as well as the return type. This is OK since the
	variable that stores the result is u64. We still avoid 64bit
	division here since 'user' is u32.

Fixes: bea74641e378 ("netfilter: xt_hashlimit: add rate match mode")
Signed-off-by: Vishwanath Pai <vpai@akamai.com>
---
 net/netfilter/xt_hashlimit.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
index 10d4823..1c1941e 100644
--- a/net/netfilter/xt_hashlimit.c
+++ b/net/netfilter/xt_hashlimit.c
@@ -35,6 +35,7 @@
 #include <linux/netfilter_ipv6/ip6_tables.h>
 #include <linux/netfilter/xt_hashlimit.h>
 #include <linux/mutex.h>
+#include <linux/kernel.h>
 
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
@@ -527,12 +528,12 @@ static u64 user2rate(u64 user)
 	}
 }
 
-static u64 user2rate_bytes(u64 user)
+static u64 user2rate_bytes(u32 user)
 {
 	u64 r;
 
-	r = user ? 0xFFFFFFFFULL / user : 0xFFFFFFFFULL;
-	r = (r - 1) << 4;
+	r = user ? U32_MAX / user : U32_MAX;
+	r = (r - 1) << XT_HASHLIMIT_BYTE_SHIFT;
 	return r;
 }
 
@@ -588,7 +589,8 @@ static void rateinfo_init(struct dsthash_ent *dh,
 		dh->rateinfo.prev_window = 0;
 		dh->rateinfo.current_rate = 0;
 		if (hinfo->cfg.mode & XT_HASHLIMIT_BYTES) {
-			dh->rateinfo.rate = user2rate_bytes(hinfo->cfg.avg);
+			dh->rateinfo.rate =
+				user2rate_bytes((u32)hinfo->cfg.avg);
 			if (hinfo->cfg.burst)
 				dh->rateinfo.burst =
 					hinfo->cfg.burst * dh->rateinfo.rate;
@@ -870,7 +872,7 @@ static int hashlimit_mt_check_common(const struct xt_mtchk_param *par,
 
 	/* Check for overflow. */
 	if (revision >= 3 && cfg->mode & XT_HASHLIMIT_RATE_MATCH) {
-		if (cfg->avg == 0) {
+		if (cfg->avg == 0 || cfg->avg > U32_MAX) {
 			pr_info("hashlimit invalid rate\n");
 			return -ERANGE;
 		}
-- 
1.9.1

Re: [PATCH v2] netfilter: xt_hashlimit: fix build error caused by 64bit division

[Pablo Neira Ayuso]

On Fri, Sep 08, 2017 at 01:38:58AM -0400, Vishwanath Pai wrote:
> 64bit division causes build/link errors on 32bit architectures. It
> prints out error messages like:
> 
> ERROR: "__aeabi_uldivmod" [net/netfilter/xt_hashlimit.ko] undefined!
> 
> The value of avg passed through by userspace in BYTE mode cannot exceed
> U32_MAX. Which means 64bit division in user2rate_bytes is unnecessary.
> To fix this I have changed the type of param 'user' to u32.
> 
> Since anything greater than U32_MAX is an invalid input we error out in
> hashlimit_mt_check_common() when this is the case.
> 
> Changes in v2:
> 	Making return type as u32 would cause an overflow for small
> 	values of 'user' (for example 2, 3 etc). To avoid this I bumped up
> 	'r' to u64 again as well as the return type. This is OK since the
> 	variable that stores the result is u64. We still avoid 64bit
> 	division here since 'user' is u32.

Applied, thanks.