Subject: [PATCH net-next 1/2] ipv6: Switch to higher-level SHA-1 functions

From: Eric Biggers <[email-masked]>
Date: Thu, 22 Jan 2026 21:16:55 -0800

There's now a proper SHA-1 API that follows the usual conventions for
hash function APIs: sha1_init(), sha1_update(), sha1_final(), sha1().
The only remaining user of the older low-level SHA-1 API,
sha1_init_raw() and sha1_transform(), is ipv6_generate_stable_address().
I'd like to remove this older API, which is too low-level.

Unfortunately, ipv6_generate_stable_address() does in fact skip the
SHA-1 finalization for some reason.  So the values it computes are not
standard SHA-1 values, and it sort of does want the low-level API.

Still, it's still possible to use the higher-level functions sha1_init()
and sha1_update() to get the same result, provided that the resulting
state is used directly, skipping sha1_final().

So, let's do that instead.  This will allow removing the low-level API.

Reviewed-by: Ard Biesheuvel <[email-masked]>
Signed-off-by: Eric Biggers <[email-masked]>
---
 net/ipv6/addrconf.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 7138e0e67991..6db9cf9e2a50 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -3337,15 +3337,14 @@ static bool ipv6_reserved_interfaceid(struct in6_addr address)
 static int ipv6_generate_stable_address(struct in6_addr *address,
 					u8 dad_count,
 					const struct inet6_dev *idev)
 {
 	static DEFINE_SPINLOCK(lock);
-	static __u32 digest[SHA1_DIGEST_WORDS];
-	static __u32 workspace[SHA1_WORKSPACE_WORDS];
+	static struct sha1_ctx sha_ctx;
 
 	static union {
-		char __data[SHA1_BLOCK_SIZE];
+		u8 __data[SHA1_BLOCK_SIZE];
 		struct {
 			struct in6_addr secret;
 			__be32 prefix[2];
 			unsigned char hwaddr[MAX_ADDR_LEN];
 			u8 dad_count;
@@ -3366,24 +3365,30 @@ static int ipv6_generate_stable_address(struct in6_addr *address,
 		return -1;
 
 retry:
 	spin_lock_bh(&lock);
 
-	sha1_init_raw(digest);
+	sha1_init(&sha_ctx);
+
 	memset(&data, 0, sizeof(data));
-	memset(workspace, 0, sizeof(workspace));
 	memcpy(data.hwaddr, idev->dev->perm_addr, idev->dev->addr_len);
 	data.prefix[0] = address->s6_addr32[0];
 	data.prefix[1] = address->s6_addr32[1];
 	data.secret = secret;
 	data.dad_count = dad_count;
 
-	sha1_transform(digest, data.__data, workspace);
+	sha1_update(&sha_ctx, data.__data, sizeof(data));
 
+	/*
+	 * Note that the SHA-1 finalization is omitted here, and the digest is
+	 * pulled directly from the internal SHA-1 state (making it incompatible
+	 * with standard SHA-1).  Unusual, but technically okay since the data
+	 * length is fixed and is a multiple of the SHA-1 block size.
+	 */
 	temp = *address;
-	temp.s6_addr32[2] = (__force __be32)digest[0];
-	temp.s6_addr32[3] = (__force __be32)digest[1];
+	temp.s6_addr32[2] = (__force __be32)sha_ctx.state.h[0];
+	temp.s6_addr32[3] = (__force __be32)sha_ctx.state.h[1];
 
 	spin_unlock_bh(&lock);
 
 	if (ipv6_reserved_interfaceid(temp)) {
 		dad_count++;
-- 
2.52.0