Fix Coverity findings in McEliece code

Initialize variables in constructor in gf2m_decomp_rootfind_state

Add asserts on the degree where a positive value was assumed. How
polyn_gf2m handles the degree needs some work but this should do for
now.

3 files changed, 20 insertions, 14 deletions

diff --git a/src/lib/pubkey/mce/gf2m_rootfind_dcmp.cpp b/src/lib/pubkey/mce/gf2m_rootfind_dcmp.cpp
index 008da99c1..acae036db 100644
--- a/src/lib/pubkey/mce/gf2m_rootfind_dcmp.cpp
+++ b/src/lib/pubkey/mce/gf2m_rootfind_dcmp.cpp
@@ -95,7 +95,7 @@ secure_vector<gf2m> find_roots_gf2m_decomp(const polyn_gf2m & polyn, u32bit code
    }
 
 gf2m_decomp_rootfind_state::gf2m_decomp_rootfind_state(const polyn_gf2m & polyn, u32bit the_code_length) :
-   code_length(the_code_length)
+   code_length(the_code_length), m_j(0), m_j_gray(0)
    {
    gf2m coeff_3;
    gf2m coeff_head;
@@ -105,7 +105,7 @@ gf2m_decomp_rootfind_state::gf2m_decomp_rootfind_state(const polyn_gf2m & polyn,
       {
       throw Internal_Error("Unexpected degree in gf2m_decomp_rootfind_state");
       }
-   this->m_j = 0;
+
    coeff_3 = polyn.get_coef( 3);
    coeff_head = polyn.get_coef( deg_sigma); /* dummy value for SCA CM */
    if(coeff_3 != 0)
@@ -275,7 +275,9 @@ gf2m gf2m_decomp_rootfind_state::calc_Fxj_j_neq_0( const polyn_gf2m & sigma, gf2
 
 secure_vector<gf2m> gf2m_decomp_rootfind_state::find_roots(const polyn_gf2m & sigma)
    {
-   secure_vector<gf2m> result(sigma.get_degree());
+   const int sigma_degree = sigma.get_degree();
+   BOTAN_ASSERT(sigma_degree > 0, "Valid sigma");
+   secure_vector<gf2m> result(sigma_degree);
    u32bit root_pos = 0;
 
    this->calc_Ai_zero(sigma);
diff --git a/src/lib/pubkey/mce/goppa_code.cpp b/src/lib/pubkey/mce/goppa_code.cpp
index 02908aa4f..2657beee9 100644
--- a/src/lib/pubkey/mce/goppa_code.cpp
+++ b/src/lib/pubkey/mce/goppa_code.cpp
@@ -96,8 +96,9 @@ secure_vector<gf2m> goppa_decode(const polyn_gf2m & syndrom_polyn,
       sigma.set_coef(2*i, sp_field->gf_square(u.get_coef(i)));
       }
 
-   const size_t v_deg = v.get_degree();
-   for(size_t i = 0; i <= v_deg; ++i)
+   const int v_deg = v.get_degree();
+   BOTAN_ASSERT(v_deg > 0, "Valid degree");
+   for(int i = 0; i <= v_deg; ++i)
       {
       sigma.set_coef(2*i+1, sp_field->gf_square(v.get_coef(i)));
       }
diff --git a/src/lib/pubkey/mce/polyn_gf2m.cpp b/src/lib/pubkey/mce/polyn_gf2m.cpp
index ec60213db..01a62da7d 100644
--- a/src/lib/pubkey/mce/polyn_gf2m.cpp
+++ b/src/lib/pubkey/mce/polyn_gf2m.cpp
@@ -268,7 +268,11 @@ void polyn_gf2m::remainder(polyn_gf2m &p, const polyn_gf2m & g)
    if (d >= 0) {
    gf2m la = msp_field->gf_inv_rn(g.get_lead_coef());
 
-   for (i = p.get_degree(); d >= 0; --i, --d) {
+   const int p_degree = p.get_degree();
+
+   BOTAN_ASSERT(p_degree > 0, "Valid polynomial");
+
+   for (i = p_degree; d >= 0; --i, --d) {
    if (p[i] != 0) {
    gf2m lb = msp_field->gf_mul_rrn(la, p[i]);
    for (j = 0; j < g.get_degree(); ++j)
@@ -455,6 +459,8 @@ std::pair<polyn_gf2m, polyn_gf2m> polyn_gf2m::eea_with_coefficients( const polyn
    // r0 <- g, r1 <- p, u0 <- 0, u1 <- 1
    dr = g.get_degree();
 
+   BOTAN_ASSERT(dr > 3, "Valid polynomial");
+
    polyn_gf2m r0(dr, g.msp_field);
    polyn_gf2m r1(dr - 1, g.msp_field);
    polyn_gf2m u0(dr - 1, g.msp_field);
@@ -656,18 +662,15 @@ polyn_gf2m::polyn_gf2m(int t, Botan::RandomNumberGenerator& rng, std::shared_ptr
 
 void polyn_gf2m::poly_shiftmod( const polyn_gf2m & g)
    {
-   int i, t;
-   gf2m a;
-
-   if(g.get_degree() <= 0)
+   if(g.get_degree() <= 1)
       {
-      throw Invalid_Argument("shiftmod cannot be called on polynomials of degree 0 or less");
+      throw Invalid_Argument("shiftmod cannot be called on polynomials of degree 1 or less");
       }
    std::shared_ptr<GF2m_Field> msp_field = g.msp_field;
 
-   t = g.get_degree();
-   a = msp_field->gf_div(this->coeff[t-1], g.coeff[t]);
-   for (i = t - 1; i > 0; --i)
+   int t = g.get_degree();
+   gf2m a = msp_field->gf_div(this->coeff[t-1], g.coeff[t]);
+   for (int i = t - 1; i > 0; --i)
       {
       this->coeff[i] = this->coeff[i - 1] ^ this->msp_field->gf_mul(a, g.coeff[i]);
       }