Mercurial > dropbear
view libtommath/bn_mp_read_radix.c @ 1788:1fc0012b9c38
Fix handling of replies to global requests (#112)
The current code assumes that all global requests want / need a reply.
This isn't always true and the request itself indicates if it wants a
reply or not.
It causes a specific problem with [email protected] messages.
These are sent by OpenSSH after authentication to inform the client of
potential other host keys for the host. This can be used to add a new
type of host key or to rotate host keys.
The initial information message from the server is sent as a global
request, but with want_reply set to false. This means that the server
doesn't expect an answer to this message. Instead the client needs to
send a prove request as a reply if it wants to receive proof of
ownership for the host keys.
The bug doesn't cause any current problems with due to how OpenSSH
treats receiving the failure message. It instead treats it as a
keepalive message and further ignores it.
Arguably this is a protocol violation though of Dropbear and it is only
accidental that it doesn't cause a problem with OpenSSH.
The bug was found when adding host keys support to libssh, which is more
strict protocol wise and treats the unexpected failure message an error,
also see https://gitlab.com/libssh/libssh-mirror/-/merge_requests/145
for more information.
The fix here is to honor the want_reply flag in the global request and
to only send a reply if the other side expects a reply.
author | Dirkjan Bussink <d.bussink@gmail.com> |
---|---|
date | Thu, 10 Dec 2020 16:13:13 +0100 |
parents | 1051e4eea25a |
children |
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#include "tommath_private.h" #ifdef BN_MP_READ_RADIX_C /* LibTomMath, multiple-precision integer library -- Tom St Denis */ /* SPDX-License-Identifier: Unlicense */ #define MP_TOUPPER(c) ((((c) >= 'a') && ((c) <= 'z')) ? (((c) + 'A') - 'a') : (c)) /* read a string [ASCII] in a given radix */ mp_err mp_read_radix(mp_int *a, const char *str, int radix) { mp_err err; int y; mp_sign neg; unsigned pos; char ch; /* zero the digit bignum */ mp_zero(a); /* make sure the radix is ok */ if ((radix < 2) || (radix > 64)) { return MP_VAL; } /* if the leading digit is a * minus set the sign to negative. */ if (*str == '-') { ++str; neg = MP_NEG; } else { neg = MP_ZPOS; } /* set the integer to the default of zero */ mp_zero(a); /* process each digit of the string */ while (*str != '\0') { /* if the radix <= 36 the conversion is case insensitive * this allows numbers like 1AB and 1ab to represent the same value * [e.g. in hex] */ ch = (radix <= 36) ? (char)MP_TOUPPER((int)*str) : *str; pos = (unsigned)(ch - '('); if (mp_s_rmap_reverse_sz < pos) { break; } y = (int)mp_s_rmap_reverse[pos]; /* if the char was found in the map * and is less than the given radix add it * to the number, otherwise exit the loop. */ if ((y == 0xff) || (y >= radix)) { break; } if ((err = mp_mul_d(a, (mp_digit)radix, a)) != MP_OKAY) { return err; } if ((err = mp_add_d(a, (mp_digit)y, a)) != MP_OKAY) { return err; } ++str; } /* if an illegal character was found, fail. */ if (!((*str == '\0') || (*str == '\r') || (*str == '\n'))) { mp_zero(a); return MP_VAL; } /* set the sign only if a != 0 */ if (!MP_IS_ZERO(a)) { a->sign = neg; } return MP_OKAY; } #endif