71 lines
1.8 KiB
Diff
71 lines
1.8 KiB
Diff
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diff --git a/compat.c b/compat.c
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index 2709dc5..7412a54 100644
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--- a/compat.c
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+++ b/compat.c
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@@ -167,6 +167,7 @@ compat_datafellows(const char *version)
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SSH_BUG_SCANNER },
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{ "Probe-*",
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SSH_BUG_PROBE },
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+ { "Cisco-*", SSH_BUG_MAX4096DH },
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{ NULL, 0 }
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};
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diff --git a/compat.h b/compat.h
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index a6c3f3d..d8def7d 100644
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--- a/compat.h
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+++ b/compat.h
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@@ -60,6 +60,7 @@
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#define SSH_NEW_OPENSSH 0x04000000
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#define SSH_BUG_DYNAMIC_RPORT 0x08000000
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#define SSH_BUG_CURVE25519PAD 0x10000000
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+#define SSH_BUG_MAX4096DH 0x20000000
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void enable_compat13(void);
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void enable_compat20(void);
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diff --git a/kexgexc.c b/kexgexc.c
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index 355b7ba..0a91bdd 100644
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--- a/kexgexc.c
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+++ b/kexgexc.c
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@@ -58,20 +58,37 @@ kexgex_client(Kex *kex)
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int min, max, nbits;
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DH *dh;
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+ min = DH_GRP_MIN;
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+ max = DH_GRP_MAX;
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+
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+ /* Servers with MAX4096DH need a preferred size (nbits) <= 4096.
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+ * We need to also ensure that min < nbits < max */
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+
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+ if (datafellows & SSH_BUG_MAX4096DH) {
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+ /* The largest min for these servers is 4096 */
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+ min = MIN(min, 4096);
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+ }
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+
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nbits = dh_estimate(kex->dh_need * 8);
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+ nbits = MIN(nbits, max);
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+ nbits = MAX(nbits, min);
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+
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+ if (datafellows & SSH_BUG_MAX4096DH) {
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+ /* Cannot have a nbits > 4096 for these servers */
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+ nbits = MIN(nbits, 4096);
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+ /* nbits has to be powers of two */
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+ if (nbits == 3072)
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+ nbits = 4096;
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+ }
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if (datafellows & SSH_OLD_DHGEX) {
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/* Old GEX request */
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packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD);
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packet_put_int(nbits);
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- min = DH_GRP_MIN;
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- max = DH_GRP_MAX;
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debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD(%u) sent", nbits);
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} else {
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/* New GEX request */
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- min = DH_GRP_MIN;
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- max = DH_GRP_MAX;
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packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST);
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packet_put_int(min);
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packet_put_int(nbits);
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