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Reject negative shifts for BN_rshift and BN_lshift

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The functions BN_rshift and BN_lshift shift their arguments to the right or
left by a specified number of bits. Unpredicatable results (including
crashes) can occur if a negative number is supplied for the shift value.

Thanks to Mateusz Kocielski (LogicalTrust), Marek Kroemeke and Filip Palian
for discovering and reporting this issue.

Reviewed-by: Kurt Roeckx <kurt@openssl.org>
This commit is contained in:
Matt Caswell 2015-05-19 15:19:30 +01:00
parent 2c55a0bc93
commit 7cc18d8158
4 changed files with 20 additions and 4 deletions
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3
crypto/bn/bn_err.c
View File

@ -98,6 +98,7 @@ static ERR_STRING_DATA BN_str_functs[] = {
{ERR_FUNC(BN_F_BN_GF2M_MOD_SOLVE_QUAD_ARR), "BN_GF2m_mod_solve_quad_arr"},
{ERR_FUNC(BN_F_BN_GF2M_MOD_SQR), "BN_GF2m_mod_sqr"},
{ERR_FUNC(BN_F_BN_GF2M_MOD_SQRT), "BN_GF2m_mod_sqrt"},
{ERR_FUNC(BN_F_BN_LSHIFT), "BN_lshift"},
{ERR_FUNC(BN_F_BN_MOD_EXP2_MONT), "BN_mod_exp2_mont"},
{ERR_FUNC(BN_F_BN_MOD_EXP_MONT), "BN_mod_exp_mont"},
{ERR_FUNC(BN_F_BN_MOD_EXP_MONT_CONSTTIME), "BN_mod_exp_mont_consttime"},
@ -113,6 +114,7 @@ static ERR_STRING_DATA BN_str_functs[] = {
{ERR_FUNC(BN_F_BN_NEW), "BN_new"},
{ERR_FUNC(BN_F_BN_RAND), "BN_rand"},
{ERR_FUNC(BN_F_BN_RAND_RANGE), "BN_rand_range"},
{ERR_FUNC(BN_F_BN_RSHIFT), "BN_rshift"},
{ERR_FUNC(BN_F_BN_SET_WORDS), "bn_set_words"},
{ERR_FUNC(BN_F_BN_USUB), "BN_usub"},
{0, NULL}
@ -131,6 +133,7 @@ static ERR_STRING_DATA BN_str_reasons[] = {
{ERR_REASON(BN_R_INPUT_NOT_REDUCED), "input not reduced"},
{ERR_REASON(BN_R_INVALID_LENGTH), "invalid length"},
{ERR_REASON(BN_R_INVALID_RANGE), "invalid range"},
{ERR_REASON(BN_R_INVALID_SHIFT), "invalid shift"},
{ERR_REASON(BN_R_NOT_A_SQUARE), "not a square"},
{ERR_REASON(BN_R_NOT_INITIALIZED), "not initialized"},
{ERR_REASON(BN_R_NO_INVERSE), "no inverse"},

10
crypto/bn/bn_shift.c
View File

@ -136,6 +136,11 @@ int BN_lshift(BIGNUM *r, const BIGNUM *a, int n)
bn_check_top(r);
bn_check_top(a);
if (n < 0) {
BNerr(BN_F_BN_LSHIFT, BN_R_INVALID_SHIFT);
return 0;
}
r->neg = a->neg;
nw = n / BN_BITS2;
if (bn_wexpand(r, a->top + nw + 1) == NULL)
@ -170,6 +175,11 @@ int BN_rshift(BIGNUM *r, const BIGNUM *a, int n)
bn_check_top(r);
bn_check_top(a);
if (n < 0) {
BNerr(BN_F_BN_RSHIFT, BN_R_INVALID_SHIFT);
return 0;
}
nw = n / BN_BITS2;
rb = n % BN_BITS2;
lb = BN_BITS2 - rb;

8
doc/crypto/BN_set_bit.pod
View File

@ -37,12 +37,12 @@ BN_mask_bits() truncates B<a> to an B<n> bit number
shorter than B<n> bits.
BN_lshift() shifts B<a> left by B<n> bits and places the result in
B<r> (C<r=a*2^n>). BN_lshift1() shifts B<a> left by one and places
the result in B<r> (C<r=2*a>).
B<r> (C<r=a*2^n>). Note that B<n> must be non-negative. BN_lshift1() shifts
B<a> left by one and places the result in B<r> (C<r=2*a>).
BN_rshift() shifts B<a> right by B<n> bits and places the result in
B<r> (C<r=a/2^n>). BN_rshift1() shifts B<a> right by one and places
the result in B<r> (C<r=a/2>).
B<r> (C<r=a/2^n>). Note that B<n> must be non-negative. BN_rshift1() shifts
B<a> right by one and places the result in B<r> (C<r=a/2>).
For the shift functions, B<r> and B<a> may be the same variable.

3
include/openssl/bn.h
View File

@ -711,6 +711,7 @@ void ERR_load_BN_strings(void);
# define BN_F_BN_GF2M_MOD_SOLVE_QUAD_ARR 135
# define BN_F_BN_GF2M_MOD_SQR 136
# define BN_F_BN_GF2M_MOD_SQRT 137
# define BN_F_BN_LSHIFT 145
# define BN_F_BN_MOD_EXP2_MONT 118
# define BN_F_BN_MOD_EXP_MONT 109
# define BN_F_BN_MOD_EXP_MONT_CONSTTIME 124
@ -726,6 +727,7 @@ void ERR_load_BN_strings(void);
# define BN_F_BN_NEW 113
# define BN_F_BN_RAND 114
# define BN_F_BN_RAND_RANGE 122
# define BN_F_BN_RSHIFT 146
# define BN_F_BN_SET_WORDS 144
# define BN_F_BN_USUB 115
@ -741,6 +743,7 @@ void ERR_load_BN_strings(void);
# define BN_R_INPUT_NOT_REDUCED 110
# define BN_R_INVALID_LENGTH 106
# define BN_R_INVALID_RANGE 115
# define BN_R_INVALID_SHIFT 119
# define BN_R_NOT_A_SQUARE 111
# define BN_R_NOT_INITIALIZED 107
# define BN_R_NO_INVERSE 108