diff options
author | David Woodhouse <David.Woodhouse@intel.com> | 2016-08-02 22:54:46 +0100 |
---|---|---|
committer | Matt Caswell <matt@openssl.org> | 2016-08-04 20:56:24 +0100 |
commit | 2e94723c1b5d8ab974645e83de90b248265af3cd (patch) | |
tree | a5884ed0abd57521d97fb75f53e9675be9a82155 /ssl/record | |
parent | 032924c4b4104654ff8659b4701e4ab25872a12e (diff) |
Fix ubsan 'left shift of negative value -1' error in satsub64be()
Baroque, almost uncommented code triggers behaviour which is undefined
by the C standard. You might quite reasonably not care that the code was
broken on ones-complement machines, but if we support a ubsan build then
we need to at least pretend to care.
It looks like the special-case code for 64-bit big-endian is going to
behave differently (and wrongly) on wrap-around, because it treats the
values as signed. That seems wrong, and allows replay and other attacks.
Surely you need to renegotiate and start a new epoch rather than
wrapping around to sequence number zero again?
Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
Diffstat (limited to 'ssl/record')
-rw-r--r-- | ssl/record/dtls1_bitmap.c | 61 |
1 files changed, 42 insertions, 19 deletions
diff --git a/ssl/record/dtls1_bitmap.c b/ssl/record/dtls1_bitmap.c index 9dae9b273e..ecc715d318 100644 --- a/ssl/record/dtls1_bitmap.c +++ b/ssl/record/dtls1_bitmap.c @@ -13,7 +13,7 @@ /* mod 128 saturating subtract of two 64-bit values in big-endian order */ static int satsub64be(const unsigned char *v1, const unsigned char *v2) { - int ret, sat, brw, i; + int ret, i; if (sizeof(long) == 8) do { @@ -45,28 +45,51 @@ static int satsub64be(const unsigned char *v1, const unsigned char *v2) return (int)l; } while (0); - ret = (int)v1[7] - (int)v2[7]; - sat = 0; - brw = ret >> 8; /* brw is either 0 or -1 */ - if (ret & 0x80) { - for (i = 6; i >= 0; i--) { - brw += (int)v1[i] - (int)v2[i]; - sat |= ~brw; - brw >>= 8; - } - } else { - for (i = 6; i >= 0; i--) { - brw += (int)v1[i] - (int)v2[i]; - sat |= brw; - brw >>= 8; + ret = 0; + for (i=0; i<7; i++) { + if (v1[i] > v2[i]) { + /* v1 is larger... but by how much? */ + if (v1[i] != v2[i] + 1) + return 128; + while (++i <= 6) { + if (v1[i] != 0x00 || v2[i] != 0xff) + return 128; /* too much */ + } + /* We checked all the way to the penultimate byte, + * so despite higher bytes changing we actually + * know that it only changed from (e.g.) + * ... (xx) ff ff ff ?? + * to ... (xx+1) 00 00 00 ?? + * so we add a 'bias' of 256 for the carry that + * happened, and will eventually return + * 256 + v1[7] - v2[7]. */ + ret = 256; + break; + } else if (v2[i] > v1[i]) { + /* v2 is larger... but by how much? */ + if (v2[i] != v1[i] + 1) + return -128; + while (++i <= 6) { + if (v2[i] != 0x00 || v1[i] != 0xff) + return -128; /* too much */ + } + /* Similar to the case above, we know it changed + * from ... (xx) 00 00 00 ?? + * to ... (xx-1) ff ff ff ?? + * so we add a 'bias' of -256 for the borrow, + * to return -256 + v1[7] - v2[7]. */ + ret = -256; } } - brw <<= 8; /* brw is either 0 or -256 */ - if (sat & 0xff) - return brw | 0x80; + ret += (int)v1[7] - (int)v2[7]; + + if (ret > 128) + return 128; + else if (ret < -128) + return -128; else - return brw + (ret & 0xFF); + return ret; } int dtls1_record_replay_check(SSL *s, DTLS1_BITMAP *bitmap) |