git: 6136a10e355a - stable/13 - Always clamp curve25519 keys prior to use.

[Peter Grehan]

The branch stable/13 has been updated by grehan:

URL: https://cgit.FreeBSD.org/src/commit/?id=6136a10e355a7a837edecbccbed04c34b4bc32c9

commit 6136a10e355a7a837edecbccbed04c34b4bc32c9
Author:     Peter Grehan <grehan at FreeBSD.org>
AuthorDate: 2021-02-03 09:05:09 +0000
Commit:     Peter Grehan <grehan at FreeBSD.org>
CommitDate: 2021-02-06 04:01:18 +0000

    Always clamp curve25519 keys prior to use.
    
    This fixes an issue where a private key contained bits that should
    have been cleared by the clamping process, but were passed through
    to the scalar multiplication routine and resulted in an invalid
    public key.
    
    Issue diagnosed (and an initial fix proposed) by shamaz.mazum in
    PR 252894.
    
    This fix suggested by Jason Donenfeld.
    
    PR:             252894
    Reported by:    shamaz.mazum
    
    (cherry picked from commit 5aaea4b99e5cc724e97e24a68876e8768d3d8012)
---
 sys/dev/if_wg/module/curve25519.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/sys/dev/if_wg/module/curve25519.c b/sys/dev/if_wg/module/curve25519.c
index e21d00bd2818..16f0b0337eb6 100644
--- a/sys/dev/if_wg/module/curve25519.c
+++ b/sys/dev/if_wg/module/curve25519.c
@@ -767,6 +767,7 @@ void curve25519_generic(u8 out[CURVE25519_KEY_SIZE],
 	u8 e[32];
 
 	memcpy(e, scalar, 32);
+	curve25519_clamp_secret(e);
 
 	/* The following implementation was transcribed to Coq and proven to
 	 * correspond to unary scalar multiplication in affine coordinates given