Subject: [PATCH v4 3/6] treewide: use get_random_{u8,u16}() when possible

From: "Jason A. Donenfeld" <[email-masked]>
Date: Fri, 7 Oct 2022 12:01:04 -0600

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.

Reviewed-by: Kees Cook <[email-masked]>
Acked-by: Toke Høiland-Jørgensen <[email-masked]> # for sch_cake
Signed-off-by: Jason A. Donenfeld <[email-masked]>
---
 arch/arm/kernel/signal.c                                  | 2 +-
 arch/arm64/kernel/syscall.c                               | 2 +-
 arch/s390/kernel/process.c                                | 2 +-
 arch/sparc/vdso/vma.c                                     | 2 +-
 crypto/testmgr.c                                          | 8 ++++----
 drivers/media/common/v4l2-tpg/v4l2-tpg-core.c             | 2 +-
 drivers/media/test-drivers/vivid/vivid-radio-rx.c         | 4 ++--
 .../net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c   | 2 +-
 drivers/net/hamradio/baycom_epp.c                         | 2 +-
 drivers/net/hamradio/hdlcdrv.c                            | 2 +-
 drivers/net/hamradio/yam.c                                | 2 +-
 drivers/net/wireguard/selftest/allowedips.c               | 4 ++--
 drivers/net/wireless/st/cw1200/wsm.c                      | 2 +-
 drivers/scsi/lpfc/lpfc_hbadisc.c                          | 6 +++---
 lib/cmdline_kunit.c                                       | 4 ++--
 lib/test_vmalloc.c                                        | 2 +-
 net/dccp/ipv4.c                                           | 4 ++--
 net/ipv4/datagram.c                                       | 2 +-
 net/ipv4/ip_output.c                                      | 2 +-
 net/ipv4/tcp_ipv4.c                                       | 4 ++--
 net/mac80211/scan.c                                       | 2 +-
 net/netfilter/nf_nat_core.c                               | 4 ++--
 net/sched/sch_cake.c                                      | 6 +++---
 net/sched/sch_sfb.c                                       | 2 +-
 net/sctp/socket.c                                         | 2 +-
 25 files changed, 38 insertions(+), 38 deletions(-)

diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index ea128e32e8ca..e07f359254c3 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -655,7 +655,7 @@ struct page *get_signal_page(void)
 		 PAGE_SIZE / sizeof(u32));
 
 	/* Give the signal return code some randomness */
-	offset = 0x200 + (get_random_int() & 0x7fc);
+	offset = 0x200 + (get_random_u16() & 0x7fc);
 	signal_return_offset = offset;
 
 	/* Copy signal return handlers into the page */
diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
index 733451fe7e41..d72e8f23422d 100644
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -67,7 +67,7 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
 	 *
 	 * The resulting 5 bits of entropy is seen in SP[8:4].
 	 */
-	choose_random_kstack_offset(get_random_int() & 0x1FF);
+	choose_random_kstack_offset(get_random_u16() & 0x1FF);
 }
 
 static inline bool has_syscall_work(unsigned long flags)
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/arch/sparc/vdso/vma.c b/arch/sparc/vdso/vma.c
index cc19e09b0fa1..04ee726859ca 100644
--- a/arch/sparc/vdso/vma.c
+++ b/arch/sparc/vdso/vma.c
@@ -354,7 +354,7 @@ static unsigned long vdso_addr(unsigned long start, unsigned int len)
 	unsigned int offset;
 
 	/* This loses some more bits than a modulo, but is cheaper */
-	offset = get_random_int() & (PTRS_PER_PTE - 1);
+	offset = get_random_u16() & (PTRS_PER_PTE - 1);
 	return start + (offset << PAGE_SHIFT);
 }
 
diff --git a/crypto/testmgr.c b/crypto/testmgr.c
index be45217acde4..981c637fa2ed 100644
--- a/crypto/testmgr.c
+++ b/crypto/testmgr.c
@@ -927,7 +927,7 @@ static void generate_random_bytes(u8 *buf, size_t count)
 			b = 0xff;
 			break;
 		default:
-			b = (u8)prandom_u32();
+			b = get_random_u8();
 			break;
 		}
 		memset(buf, b, count);
@@ -935,8 +935,8 @@ static void generate_random_bytes(u8 *buf, size_t count)
 		break;
 	case 2:
 		/* Ascending or descending bytes, plus optional mutations */
-		increment = (u8)prandom_u32();
-		b = (u8)prandom_u32();
+		increment = get_random_u8();
+		b = get_random_u8();
 		for (i = 0; i < count; i++, b += increment)
 			buf[i] = b;
 		mutate_buffer(buf, count);
@@ -944,7 +944,7 @@ static void generate_random_bytes(u8 *buf, size_t count)
 	default:
 		/* Fully random bytes */
 		for (i = 0; i < count; i++)
-			buf[i] = (u8)prandom_u32();
+			buf[i] = get_random_u8();
 	}
 }
 
diff --git a/drivers/media/common/v4l2-tpg/v4l2-tpg-core.c b/drivers/media/common/v4l2-tpg/v4l2-tpg-core.c
index 9b7bcdce6e44..303d02b1d71c 100644
--- a/drivers/media/common/v4l2-tpg/v4l2-tpg-core.c
+++ b/drivers/media/common/v4l2-tpg/v4l2-tpg-core.c
@@ -870,7 +870,7 @@ static void precalculate_color(struct tpg_data *tpg, int k)
 		g = tpg_colors[col].g;
 		b = tpg_colors[col].b;
 	} else if (tpg->pattern == TPG_PAT_NOISE) {
-		r = g = b = prandom_u32_max(256);
+		r = g = b = get_random_u8();
 	} else if (k == TPG_COLOR_RANDOM) {
 		r = g = b = tpg->qual_offset + prandom_u32_max(196);
 	} else if (k >= TPG_COLOR_RAMP) {
diff --git a/drivers/media/test-drivers/vivid/vivid-radio-rx.c b/drivers/media/test-drivers/vivid/vivid-radio-rx.c
index 232cab508f48..8bd09589fb15 100644
--- a/drivers/media/test-drivers/vivid/vivid-radio-rx.c
+++ b/drivers/media/test-drivers/vivid/vivid-radio-rx.c
@@ -104,8 +104,8 @@ ssize_t vivid_radio_rx_read(struct file *file, char __user *buf,
 				break;
 			case 2:
 				rds.block |= V4L2_RDS_BLOCK_ERROR;
-				rds.lsb = prandom_u32_max(256);
-				rds.msb = prandom_u32_max(256);
+				rds.lsb = get_random_u8();
+				rds.msb = get_random_u8();
 				break;
 			case 3: /* Skip block altogether */
 				if (i)
diff --git a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c
index ddfe9208529a..ac452a0111a9 100644
--- a/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c
+++ b/drivers/net/ethernet/chelsio/inline_crypto/chtls/chtls_cm.c
@@ -1467,7 +1467,7 @@ static void make_established(struct sock *sk, u32 snd_isn, unsigned int opt)
 	tp->write_seq = snd_isn;
 	tp->snd_nxt = snd_isn;
 	tp->snd_una = snd_isn;
-	inet_sk(sk)->inet_id = prandom_u32();
+	inet_sk(sk)->inet_id = get_random_u16();
 	assign_rxopt(sk, opt);
 
 	if (tp->rcv_wnd > (RCV_BUFSIZ_M << 10))
diff --git a/drivers/net/hamradio/baycom_epp.c b/drivers/net/hamradio/baycom_epp.c
index 7df78a721b04..791b4a53d69f 100644
--- a/drivers/net/hamradio/baycom_epp.c
+++ b/drivers/net/hamradio/baycom_epp.c
@@ -438,7 +438,7 @@ static int transmit(struct baycom_state *bc, int cnt, unsigned char stat)
 			if ((--bc->hdlctx.slotcnt) > 0)
 				return 0;
 			bc->hdlctx.slotcnt = bc->ch_params.slottime;
-			if (prandom_u32_max(256) > bc->ch_params.ppersist)
+			if (get_random_u8() > bc->ch_params.ppersist)
 				return 0;
 		}
 	}
diff --git a/drivers/net/hamradio/hdlcdrv.c b/drivers/net/hamradio/hdlcdrv.c
index 360d041a62c4..6c6f11d3d0aa 100644
--- a/drivers/net/hamradio/hdlcdrv.c
+++ b/drivers/net/hamradio/hdlcdrv.c
@@ -377,7 +377,7 @@ void hdlcdrv_arbitrate(struct net_device *dev, struct hdlcdrv_state *s)
 	if ((--s->hdlctx.slotcnt) > 0)
 		return;
 	s->hdlctx.slotcnt = s->ch_params.slottime;
-	if (prandom_u32_max(256) > s->ch_params.ppersist)
+	if (get_random_u8() > s->ch_params.ppersist)
 		return;
 	start_tx(dev, s);
 }
diff --git a/drivers/net/hamradio/yam.c b/drivers/net/hamradio/yam.c
index 97a6cc5c7ae8..2ed2f836f09a 100644
--- a/drivers/net/hamradio/yam.c
+++ b/drivers/net/hamradio/yam.c
@@ -626,7 +626,7 @@ static void yam_arbitrate(struct net_device *dev)
 	yp->slotcnt = yp->slot / 10;
 
 	/* is random > persist ? */
-	if (prandom_u32_max(256) > yp->pers)
+	if (get_random_u8() > yp->pers)
 		return;
 
 	yam_start_tx(dev, yp);
diff --git a/drivers/net/wireguard/selftest/allowedips.c b/drivers/net/wireguard/selftest/allowedips.c
index 41db10f9be49..dd897c0740a2 100644
--- a/drivers/net/wireguard/selftest/allowedips.c
+++ b/drivers/net/wireguard/selftest/allowedips.c
@@ -310,7 +310,7 @@ static __init bool randomized_test(void)
 			for (k = 0; k < 4; ++k)
 				mutated[k] = (mutated[k] & mutate_mask[k]) |
 					     (~mutate_mask[k] &
-					      prandom_u32_max(256));
+					      get_random_u8());
 			cidr = prandom_u32_max(32) + 1;
 			peer = peers[prandom_u32_max(NUM_PEERS)];
 			if (wg_allowedips_insert_v4(&t,
@@ -354,7 +354,7 @@ static __init bool randomized_test(void)
 			for (k = 0; k < 4; ++k)
 				mutated[k] = (mutated[k] & mutate_mask[k]) |
 					     (~mutate_mask[k] &
-					      prandom_u32_max(256));
+					      get_random_u8());
 			cidr = prandom_u32_max(128) + 1;
 			peer = peers[prandom_u32_max(NUM_PEERS)];
 			if (wg_allowedips_insert_v6(&t,
diff --git a/drivers/net/wireless/st/cw1200/wsm.c b/drivers/net/wireless/st/cw1200/wsm.c
index 5a3e7a626702..4a9e4b5d3547 100644
--- a/drivers/net/wireless/st/cw1200/wsm.c
+++ b/drivers/net/wireless/st/cw1200/wsm.c
@@ -1594,7 +1594,7 @@ static int cw1200_get_prio_queue(struct cw1200_common *priv,
 		edca = &priv->edca.params[i];
 		score = ((edca->aifns + edca->cwmin) << 16) +
 			((edca->cwmax - edca->cwmin) *
-			 (get_random_int() & 0xFFFF));
+			 get_random_u16());
 		if (score < best && (winner < 0 || i != 3)) {
 			best = score;
 			winner = i;
diff --git a/drivers/scsi/lpfc/lpfc_hbadisc.c b/drivers/scsi/lpfc/lpfc_hbadisc.c
index 2645def612e6..26d1779cb570 100644
--- a/drivers/scsi/lpfc/lpfc_hbadisc.c
+++ b/drivers/scsi/lpfc/lpfc_hbadisc.c
@@ -2150,8 +2150,8 @@ lpfc_check_pending_fcoe_event(struct lpfc_hba *phba, uint8_t unreg_fcf)
  * This function makes an running random selection decision on FCF record to
  * use through a sequence of @fcf_cnt eligible FCF records with equal
  * probability. To perform integer manunipulation of random numbers with
- * size unit32_t, the lower 16 bits of the 32-bit random number returned
- * from prandom_u32() are taken as the random random number generated.
+ * size unit32_t, a 16-bit random number returned from get_random_u16() is
+ * taken as the random random number generated.
  *
  * Returns true when outcome is for the newly read FCF record should be
  * chosen; otherwise, return false when outcome is for keeping the previously
@@ -2163,7 +2163,7 @@ lpfc_sli4_new_fcf_random_select(struct lpfc_hba *phba, uint32_t fcf_cnt)
 	uint32_t rand_num;
 
 	/* Get 16-bit uniform random number */
-	rand_num = 0xFFFF & prandom_u32();
+	rand_num = get_random_u16();
 
 	/* Decision with probability 1/fcf_cnt */
 	if ((fcf_cnt * rand_num) < 0xFFFF)
diff --git a/lib/cmdline_kunit.c b/lib/cmdline_kunit.c
index a72a2c16066e..d4572dbc9145 100644
--- a/lib/cmdline_kunit.c
+++ b/lib/cmdline_kunit.c
@@ -76,7 +76,7 @@ static void cmdline_test_lead_int(struct kunit *test)
 		int rc = cmdline_test_values[i];
 		int offset;
 
-		sprintf(in, "%u%s", get_random_int() % 256, str);
+		sprintf(in, "%u%s", get_random_u8(), str);
 		/* Only first '-' after the number will advance the pointer */
 		offset = strlen(in) - strlen(str) + !!(rc == 2);
 		cmdline_do_one_test(test, in, rc, offset);
@@ -94,7 +94,7 @@ static void cmdline_test_tail_int(struct kunit *test)
 		int rc = strcmp(str, "") ? (strcmp(str, "-") ? 0 : 1) : 1;
 		int offset;
 
-		sprintf(in, "%s%u", str, get_random_int() % 256);
+		sprintf(in, "%s%u", str, get_random_u8());
 		/*
 		 * Only first and leading '-' not followed by integer
 		 * will advance the pointer.
diff --git a/lib/test_vmalloc.c b/lib/test_vmalloc.c
index 56ffaa8dd3f6..0131ed2cd1bd 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/dccp/ipv4.c b/net/dccp/ipv4.c
index da6e3b20cd75..301799e7fa56 100644
--- a/net/dccp/ipv4.c
+++ b/net/dccp/ipv4.c
@@ -123,7 +123,7 @@ int dccp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 						    inet->inet_daddr,
 						    inet->inet_sport,
 						    inet->inet_dport);
-	inet->inet_id = prandom_u32();
+	inet->inet_id = get_random_u16();
 
 	err = dccp_connect(sk);
 	rt = NULL;
@@ -422,7 +422,7 @@ struct sock *dccp_v4_request_recv_sock(const struct sock *sk,
 	RCU_INIT_POINTER(newinet->inet_opt, rcu_dereference(ireq->ireq_opt));
 	newinet->mc_index  = inet_iif(skb);
 	newinet->mc_ttl	   = ip_hdr(skb)->ttl;
-	newinet->inet_id   = prandom_u32();
+	newinet->inet_id   = get_random_u16();
 
 	if (dst == NULL && (dst = inet_csk_route_child_sock(sk, newsk, req)) == NULL)
 		goto put_and_exit;
diff --git a/net/ipv4/datagram.c b/net/ipv4/datagram.c
index ffd57523331f..fefc5d855a66 100644
--- a/net/ipv4/datagram.c
+++ b/net/ipv4/datagram.c
@@ -71,7 +71,7 @@ int __ip4_datagram_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len
 	reuseport_has_conns(sk, true);
 	sk->sk_state = TCP_ESTABLISHED;
 	sk_set_txhash(sk);
-	inet->inet_id = prandom_u32();
+	inet->inet_id = get_random_u16();
 
 	sk_dst_set(sk, &rt->dst);
 	err = 0;
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/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 5b019ba2b9d2..747752980983 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -303,7 +303,7 @@ int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 						 inet->inet_daddr);
 	}
 
-	inet->inet_id = prandom_u32();
+	inet->inet_id = get_random_u16();
 
 	if (tcp_fastopen_defer_connect(sk, &err))
 		return err;
@@ -1523,7 +1523,7 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
 	inet_csk(newsk)->icsk_ext_hdr_len = 0;
 	if (inet_opt)
 		inet_csk(newsk)->icsk_ext_hdr_len = inet_opt->opt.optlen;
-	newinet->inet_id = prandom_u32();
+	newinet->inet_id = get_random_u16();
 
 	/* Set ToS of the new socket based upon the value of incoming SYN.
 	 * ECT bits are set later in tcp_init_transfer().
diff --git a/net/mac80211/scan.c b/net/mac80211/scan.c
index c4f2aeb31da3..6cab549cc421 100644
--- a/net/mac80211/scan.c
+++ b/net/mac80211/scan.c
@@ -641,7 +641,7 @@ static void ieee80211_send_scan_probe_req(struct ieee80211_sub_if_data *sdata,
 		if (flags & IEEE80211_PROBE_FLAG_RANDOM_SN) {
 			struct ieee80211_hdr *hdr = (void *)skb->data;
 			struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
-			u16 sn = get_random_u32();
+			u16 sn = get_random_u16();
 
 			info->control.flags |= IEEE80211_TX_CTRL_NO_SEQNO;
 			hdr->seq_ctrl =
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/sched/sch_cake.c b/net/sched/sch_cake.c
index a43a58a73d09..637ef1757931 100644
--- a/net/sched/sch_cake.c
+++ b/net/sched/sch_cake.c
@@ -2092,11 +2092,11 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch)
 
 		WARN_ON(host_load > CAKE_QUEUES);
 
-		/* The shifted prandom_u32() is a way to apply dithering to
-		 * avoid accumulating roundoff errors
+		/* The get_random_u16() is a way to apply dithering to avoid
+		 * accumulating roundoff errors
 		 */
 		flow->deficit += (b->flow_quantum * quantum_div[host_load] +
-				  (prandom_u32() >> 16)) >> 16;
+				  get_random_u16()) >> 16;
 		list_move_tail(&flow->flowchain, &b->old_flows);
 
 		goto retry;
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)) {
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 1e354ba44960..83628c347744 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -9448,7 +9448,7 @@ void sctp_copy_sock(struct sock *newsk, struct sock *sk,
 	newinet->inet_rcv_saddr = inet->inet_rcv_saddr;
 	newinet->inet_dport = htons(asoc->peer.port);
 	newinet->pmtudisc = inet->pmtudisc;
-	newinet->inet_id = prandom_u32();
+	newinet->inet_id = get_random_u16();
 
 	newinet->uc_ttl = inet->uc_ttl;
 	newinet->mc_loop = 1;
-- 
2.37.3