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

Jason A. Donenfeld
2022-10-08T05:58:11Z

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@chromium.org>
Signed-off-by: Jason A. Donenfeld <Jason@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