[PATCH v5 4/7] treewide: use get_random_{u8,u16}() when possible, part 2

[Jason A. Donenfeld]

Rather than truncate a 32-bit value to a 16-bit value or an 8-bit value,
simply use the get_random_{u8,u16}() functions, which are faster than
wasting the additional bytes from a 32-bit value. This was done by hand,
identifying all of the places where one of the random integer functions
was used in a non-32-bit context.

Reviewed-by: Kees Cook <keescook at chromium.org>
Signed-off-by: Jason A. Donenfeld <Jason at zx2c4.com>
---
 arch/s390/kernel/process.c  | 2 +-
 lib/test_vmalloc.c          | 2 +-
 net/ipv4/ip_output.c        | 2 +-
 net/netfilter/nf_nat_core.c | 4 ++--
 net/rds/bind.c              | 2 +-
 net/sched/sch_sfb.c         | 2 +-
 6 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/s390/kernel/process.c b/arch/s390/kernel/process.c
index 5ec78555dd2e..42af4b3aa02b 100644
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -230,7 +230,7 @@ unsigned long arch_align_stack(unsigned long sp)
 
 static inline unsigned long brk_rnd(void)
 {
-	return (get_random_int() & BRK_RND_MASK) << PAGE_SHIFT;
+	return (get_random_u16() & BRK_RND_MASK) << PAGE_SHIFT;
 }
 
 unsigned long arch_randomize_brk(struct mm_struct *mm)
diff --git a/lib/test_vmalloc.c b/lib/test_vmalloc.c
index a26bbbf20e62..cf7780572f5b 100644
--- a/lib/test_vmalloc.c
+++ b/lib/test_vmalloc.c
@@ -80,7 +80,7 @@ static int random_size_align_alloc_test(void)
 	int i;
 
 	for (i = 0; i < test_loop_count; i++) {
-		rnd = prandom_u32();
+		rnd = get_random_u8();
 
 		/*
 		 * Maximum 1024 pages, if PAGE_SIZE is 4096.
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 04e2034f2f8e..a4fbdbff14b3 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -172,7 +172,7 @@ int ip_build_and_send_pkt(struct sk_buff *skb, const struct sock *sk,
 		 * Avoid using the hashed IP ident generator.
 		 */
 		if (sk->sk_protocol == IPPROTO_TCP)
-			iph->id = (__force __be16)prandom_u32();
+			iph->id = (__force __be16)get_random_u16();
 		else
 			__ip_select_ident(net, iph, 1);
 	}
diff --git a/net/netfilter/nf_nat_core.c b/net/netfilter/nf_nat_core.c
index 7981be526f26..57c7686ac485 100644
--- a/net/netfilter/nf_nat_core.c
+++ b/net/netfilter/nf_nat_core.c
@@ -468,7 +468,7 @@ static void nf_nat_l4proto_unique_tuple(struct nf_conntrack_tuple *tuple,
 	if (range->flags & NF_NAT_RANGE_PROTO_OFFSET)
 		off = (ntohs(*keyptr) - ntohs(range->base_proto.all));
 	else
-		off = prandom_u32();
+		off = get_random_u16();
 
 	attempts = range_size;
 	if (attempts > max_attempts)
@@ -490,7 +490,7 @@ static void nf_nat_l4proto_unique_tuple(struct nf_conntrack_tuple *tuple,
 	if (attempts >= range_size || attempts < 16)
 		return;
 	attempts /= 2;
-	off = prandom_u32();
+	off = get_random_u16();
 	goto another_round;
 }
 
diff --git a/net/rds/bind.c b/net/rds/bind.c
index 5b5fb4ca8d3e..97a29172a8ee 100644
--- a/net/rds/bind.c
+++ b/net/rds/bind.c
@@ -104,7 +104,7 @@ static int rds_add_bound(struct rds_sock *rs, const struct in6_addr *addr,
 			return -EINVAL;
 		last = rover;
 	} else {
-		rover = max_t(u16, prandom_u32(), 2);
+		rover = max_t(u16, get_random_u16(), 2);
 		last = rover - 1;
 	}
 
diff --git a/net/sched/sch_sfb.c b/net/sched/sch_sfb.c
index 2829455211f8..7eb70acb4d58 100644
--- a/net/sched/sch_sfb.c
+++ b/net/sched/sch_sfb.c
@@ -379,7 +379,7 @@ static int sfb_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 		goto enqueue;
 	}
 
-	r = prandom_u32() & SFB_MAX_PROB;
+	r = get_random_u16() & SFB_MAX_PROB;
 
 	if (unlikely(r < p_min)) {
 		if (unlikely(p_min > SFB_MAX_PROB / 2)) {
-- 
2.37.3