niceSOFT/libssh | Gitverse

src/bind_config.c
719 строк22 KB
Jakub Jelen
CVE-2026-0965 config: Do not attempt to read non-regular and too large configuration files
06 фев 2026, 11:55
06 фев 2026, 11:55bf390a0
/*
 * bind_config.c - Parse the SSH server configuration file
 *
 * This file is part of the SSH Library
 *
 * Copyright (c) 2019 by Red Hat, Inc.
 *
 * Author: Anderson Toshiyuki Sasaki <ansasaki@redhat.com>
 *
 * The SSH Library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or (at your
 * option) any later version.
 *
 * The SSH Library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with the SSH Library; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

#include "config.h"

#include <ctype.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#ifdef HAVE_GLOB_H
# include <glob.h>
#endif

#include "libssh/bind.h"
#include "libssh/bind_config.h"
#include "libssh/config_parser.h"
#include "libssh/priv.h"
#include "libssh/server.h"
#include "libssh/options.h"

#ifndef MAX_LINE_SIZE
#define MAX_LINE_SIZE 1024
#endif

/* Flags used for the parser state */
#define PARSING     1
#define IN_MATCH    (1<<1)

struct ssh_bind_config_keyword_table_s {
  const char *name;
  enum ssh_bind_config_opcode_e opcode;
  bool allowed_in_match;
};

static struct ssh_bind_config_keyword_table_s
ssh_bind_config_keyword_table[] = {
    {
        .name   = "include",
        .opcode = BIND_CFG_INCLUDE
    },
    {
        .name   = "hostkey",
        .opcode = BIND_CFG_HOSTKEY
    },
    {
        .name   = "listenaddress",
        .opcode = BIND_CFG_LISTENADDRESS
    },
    {
        .name   = "port",
        .opcode = BIND_CFG_PORT
    },
    {
        .name   = "loglevel",
        .opcode = BIND_CFG_LOGLEVEL,
        .allowed_in_match = true,
    },
    {
        .name   = "ciphers",
        .opcode = BIND_CFG_CIPHERS
    },
    {
        .name   = "macs",
        .opcode = BIND_CFG_MACS
    },
    {
        .name   = "kexalgorithms",
        .opcode = BIND_CFG_KEXALGORITHMS
    },
    {
        .name   = "match",
        .opcode = BIND_CFG_MATCH,
        .allowed_in_match = true
    },
    {
        .name   = "pubkeyacceptedkeytypes",
        .opcode = BIND_CFG_PUBKEY_ACCEPTED_KEY_TYPES,
        .allowed_in_match = true
    },
    {
        .name   = "hostkeyalgorithms",
        .opcode = BIND_CFG_HOSTKEY_ALGORITHMS,
        .allowed_in_match = true
    },
    {
        .opcode = BIND_CFG_UNKNOWN,
    }
};

enum ssh_bind_config_match_e {
    BIND_MATCH_UNKNOWN = -1,
    BIND_MATCH_ALL,
    BIND_MATCH_USER,
    BIND_MATCH_GROUP,
    BIND_MATCH_HOST,
    BIND_MATCH_LOCALADDRESS,
    BIND_MATCH_LOCALPORT,
    BIND_MATCH_RDOMAIN,
    BIND_MATCH_ADDRESS,
};

struct ssh_bind_config_match_keyword_table_s {
    const char *name;
    enum ssh_bind_config_match_e opcode;
};

static struct ssh_bind_config_match_keyword_table_s
ssh_bind_config_match_keyword_table[] = {
    {
        .name   = "all",
        .opcode = BIND_MATCH_ALL
    },
    {
        .name   = "user",
        .opcode = BIND_MATCH_USER
    },
    {
        .name   = "group",
        .opcode = BIND_MATCH_GROUP
    },
    {
        .name   = "host",
        .opcode = BIND_MATCH_HOST
    },
    {
        .name   = "localaddress",
        .opcode = BIND_MATCH_LOCALADDRESS
    },
    {
        .name   = "localport",
        .opcode = BIND_MATCH_LOCALPORT
    },
    {
        .name   = "rdomain",
        .opcode = BIND_MATCH_RDOMAIN
    },
    {
        .name   = "address",
        .opcode = BIND_MATCH_ADDRESS
    },
    {
        .opcode = BIND_MATCH_UNKNOWN
    },
};

static enum ssh_bind_config_opcode_e
ssh_bind_config_get_opcode(char *keyword, uint32_t *parser_flags)
{
    int i;

    for (i = 0; ssh_bind_config_keyword_table[i].name != NULL; i++) {
        if (strcasecmp(keyword, ssh_bind_config_keyword_table[i].name) == 0) {
            if ((*parser_flags & IN_MATCH) &&
                !(ssh_bind_config_keyword_table[i].allowed_in_match))
            {
                return BIND_CFG_NOT_ALLOWED_IN_MATCH;
            }
            return ssh_bind_config_keyword_table[i].opcode;
        }
    }

    return BIND_CFG_UNKNOWN;
}

static int
ssh_bind_config_parse_line(ssh_bind bind,
                           const char *line,
                           unsigned int count,
                           uint32_t *parser_flags,
                           uint8_t *seen,
                           unsigned int depth);

#define LIBSSH_BIND_CONF_MAX_DEPTH 16
static void
local_parse_file(ssh_bind bind,
                 const char *filename,
                 uint32_t *parser_flags,
                 uint8_t *seen,
                 unsigned int depth)
{
    FILE *f = NULL;
    char line[MAX_LINE_SIZE] = {0};
    unsigned int count = 0;
    int rv;

    if (depth > LIBSSH_BIND_CONF_MAX_DEPTH) {
        ssh_set_error(bind, SSH_FATAL,
                      "ERROR - Too many levels of configuration includes "
                      "when processing file '%s'", filename);
        return;
    }

    f = ssh_strict_fopen(filename, SSH_MAX_CONFIG_FILE_SIZE);
    if (f == NULL) {
        SSH_LOG(SSH_LOG_RARE, "Cannot find file %s to load",
                filename);
        return;
    }

    SSH_LOG(SSH_LOG_PACKET, "Reading additional configuration data from %s",
            filename);

    while (fgets(line, sizeof(line), f)) {
        count++;
        rv = ssh_bind_config_parse_line(bind, line, count, parser_flags, seen, depth);
        if (rv < 0) {
            fclose(f);
            return;
        }
    }

    fclose(f);
    return;
}

#if defined(HAVE_GLOB) && defined(HAVE_GLOB_GL_FLAGS_MEMBER)
static void local_parse_glob(ssh_bind bind,
                             const char *fileglob,
                             uint32_t *parser_flags,
                             uint8_t *seen,
                             unsigned int depth)
{
    glob_t globbuf = {
        .gl_flags = 0,
    };
    int rt;
    u_int i;

    rt = glob(fileglob, GLOB_TILDE, NULL, &globbuf);
    if (rt == GLOB_NOMATCH) {
        globfree(&globbuf);
        return;
    } else if (rt != 0) {
        SSH_LOG(SSH_LOG_RARE, "Glob error: %s",
                fileglob);
        globfree(&globbuf);
        return;
    }

    for (i = 0; i < globbuf.gl_pathc; i++) {
        local_parse_file(bind, globbuf.gl_pathv[i], parser_flags, seen, depth);
    }

    globfree(&globbuf);
}
#endif /* HAVE_GLOB HAVE_GLOB_GL_FLAGS_MEMBER */

static enum ssh_bind_config_match_e
ssh_bind_config_get_match_opcode(const char *keyword)
{
    size_t i;

    for (i = 0; ssh_bind_config_match_keyword_table[i].name != NULL; i++) {
        if (strcasecmp(keyword, ssh_bind_config_match_keyword_table[i].name) == 0) {
            return ssh_bind_config_match_keyword_table[i].opcode;
        }
    }

    return BIND_MATCH_UNKNOWN;
}

static int
ssh_bind_config_parse_line(ssh_bind bind,
                           const char *line,
                           unsigned int count,
                           uint32_t *parser_flags,
                           uint8_t *seen,
                           unsigned int depth)
{
    enum ssh_bind_config_opcode_e opcode;
    const char *p = NULL;
    char *s = NULL, *x = NULL;
    char *keyword = NULL;
    size_t len;

    int rc = 0;

    if (bind == NULL) {
        return -1;
    }

    /* Ignore empty lines */
    if (line == NULL || *line == '\0') {
        return 0;
    }

    if (parser_flags == NULL) {
        ssh_set_error_invalid(bind);
        return -1;
    }

    x = s = strdup(line);
    if (s == NULL) {
        ssh_set_error_oom(bind);
        return -1;
    }

    /* Remove trailing spaces */
    for (len = strlen(s) - 1; len > 0; len--) {
        if (! isspace(s[len])) {
            break;
        }
        s[len] = '\0';
    }

    keyword = ssh_config_get_token(&s);
    if (keyword == NULL || *keyword == '#' ||
            *keyword == '\0' || *keyword == '\n') {
        SAFE_FREE(x);
        return 0;
    }

    opcode = ssh_bind_config_get_opcode(keyword, parser_flags);
    if ((*parser_flags & PARSING) &&
            opcode != BIND_CFG_HOSTKEY &&
            opcode != BIND_CFG_INCLUDE &&
            opcode != BIND_CFG_MATCH &&
            opcode > BIND_CFG_UNSUPPORTED) { /* Ignore all unknown types here */
        /* Skip all the options that were already applied */
        if (seen[opcode] != 0) {
            SAFE_FREE(x);
            return 0;
        }
        seen[opcode] = 1;
    }

    switch (opcode) {
    case BIND_CFG_INCLUDE:
        p = ssh_config_get_str_tok(&s, NULL);
        if (p && (*parser_flags & PARSING)) {
#if defined(HAVE_GLOB) && defined(HAVE_GLOB_GL_FLAGS_MEMBER)
            local_parse_glob(bind, p, parser_flags, seen, depth + 1);
#else
            local_parse_file(bind, p, parser_flags, seen, depth + 1);
#endif /* HAVE_GLOB */
        }
        break;

    case BIND_CFG_HOSTKEY:
        p = ssh_config_get_str_tok(&s, NULL);
        if (p && (*parser_flags & PARSING)) {
            rc = ssh_bind_options_set(bind, SSH_BIND_OPTIONS_HOSTKEY, p);
            if (rc != 0) {
                SSH_LOG(SSH_LOG_TRACE,
                        "line %d: Failed to set Hostkey value '%s'",
                        count, p);
            }
        }
        break;
    case BIND_CFG_LISTENADDRESS:
        p = ssh_config_get_str_tok(&s, NULL);
        if (p && (*parser_flags & PARSING)) {
            rc = ssh_bind_options_set(bind, SSH_BIND_OPTIONS_BINDADDR, p);
            if (rc != 0) {
                SSH_LOG(SSH_LOG_TRACE,
                        "line %d: Failed to set ListenAddress value '%s'",
                        count, p);
            }
        }
        break;
    case BIND_CFG_PORT:
        p = ssh_config_get_str_tok(&s, NULL);
        if (p && (*parser_flags & PARSING)) {
            rc = ssh_bind_options_set(bind, SSH_BIND_OPTIONS_BINDPORT_STR, p);
            if (rc != 0) {
                SSH_LOG(SSH_LOG_TRACE,
                        "line %d: Failed to set Port value '%s'",
                        count, p);
            }
        }
        break;
    case BIND_CFG_CIPHERS:
        p = ssh_config_get_str_tok(&s, NULL);
        if (p && (*parser_flags & PARSING)) {
            rc = ssh_bind_options_set(bind, SSH_BIND_OPTIONS_CIPHERS_C_S, p);
            if (rc != 0) {
                SSH_LOG(SSH_LOG_TRACE,
                        "line %d: Failed to set C->S Ciphers value '%s'",
                        count, p);
                break;
            }

            rc = ssh_bind_options_set(bind, SSH_BIND_OPTIONS_CIPHERS_S_C, p);
            if (rc != 0) {
                SSH_LOG(SSH_LOG_TRACE,
                        "line %d: Failed to set S->C Ciphers value '%s'",
                        count, p);
            }
        }
        break;
    case BIND_CFG_MACS:
        p = ssh_config_get_str_tok(&s, NULL);
        if (p && (*parser_flags & PARSING)) {
            rc = ssh_bind_options_set(bind, SSH_BIND_OPTIONS_HMAC_C_S, p);
            if (rc != 0) {
                SSH_LOG(SSH_LOG_TRACE,
                        "line %d: Failed to set C->S MAC value '%s'",
                        count, p);
                break;
            }

            rc = ssh_bind_options_set(bind, SSH_BIND_OPTIONS_HMAC_S_C, p);
            if (rc != 0) {
                SSH_LOG(SSH_LOG_TRACE,
                        "line %d: Failed to set S->C MAC value '%s'",
                        count, p);
            }
        }
        break;
    case BIND_CFG_LOGLEVEL:
        p = ssh_config_get_str_tok(&s, NULL);
        if (p && (*parser_flags & PARSING)) {
            int value = -1;

            if (strcasecmp(p, "quiet") == 0) {
                value = SSH_LOG_NONE;
            } else if (strcasecmp(p, "fatal") == 0 ||
                    strcasecmp(p, "error")== 0) {
                value = SSH_LOG_WARN;
            } else if (strcasecmp(p, "verbose") == 0 ||
                    strcasecmp(p, "info") == 0) {
                value = SSH_LOG_INFO;
            } else if (strcasecmp(p, "DEBUG") == 0 ||
                    strcasecmp(p, "DEBUG1") == 0) {
                value = SSH_LOG_DEBUG;
            } else if (strcasecmp(p, "DEBUG2") == 0 ||
                    strcasecmp(p, "DEBUG3") == 0) {
                value = SSH_LOG_TRACE;
            }
            if (value != -1) {
                rc = ssh_bind_options_set(bind, SSH_BIND_OPTIONS_LOG_VERBOSITY,
                        &value);
                if (rc != 0) {
                    SSH_LOG(SSH_LOG_TRACE,
                            "line %d: Failed to set LogLevel value '%s'",
                            count, p);
                }
            }
        }
        break;
    case BIND_CFG_KEXALGORITHMS:
        p = ssh_config_get_str_tok(&s, NULL);
        if (p && (*parser_flags & PARSING)) {
            rc = ssh_bind_options_set(bind, SSH_BIND_OPTIONS_KEY_EXCHANGE, p);
            if (rc != 0) {
                SSH_LOG(SSH_LOG_TRACE,
                        "line %d: Failed to set KexAlgorithms value '%s'",
                        count, p);
            }
        }
        break;
    case BIND_CFG_MATCH: {
        bool negate;
        int result = PARSING;
        size_t args = 0;
        enum ssh_bind_config_match_e opt;
        const char *p2 = NULL;

        /* The options set in Match blocks should be applied when a connection
         * is accepted, and not right away when parsing the file (as it is
         * currently done). This means the configuration files should be parsed
         * again or the options set in the Match blocks should be stored and
         * applied as necessary. */

        /* If this is the first Match block, erase the seen table to allow
         * options to be overridden. Erasing the seen table was the easiest way
         * to allow overriding an option, but only for the first occurrence of
         * an option in a Match block. This is sufficient for the current
         * implementation which supports only the 'All' criterion, meaning the
         * options can be applied right away. */
        if (!(*parser_flags & IN_MATCH)) {
            memset(seen, 0x00, BIND_CFG_MAX * sizeof(uint8_t));
        }

        /* In this line the PARSING bit is cleared from the flags */
        *parser_flags = IN_MATCH;
        do {
            p = p2 = ssh_config_get_str_tok(&s, NULL);
            if (p == NULL || p[0] == '\0') {
                break;
            }
            args++;
            SSH_LOG(SSH_LOG_TRACE, "line %d: Processing Match keyword '%s'",
                    count, p);

            /* If the option is prefixed with ! the result should be negated */
            negate = false;
            if (p[0] == '!') {
                negate = true;
                p++;
            }

            opt = ssh_bind_config_get_match_opcode(p);
            switch (opt) {
            case BIND_MATCH_ALL:
                p = ssh_config_get_str_tok(&s, NULL);
                if ((args == 1) && (p == NULL || p[0] == '\0')) {
                    /* The "all" keyword does not accept arguments or modifiers
                     */
                    if (negate == true) {
                        result = 0;
                    }
                    break;
                }
                ssh_set_error(bind, SSH_FATAL,
                              "line %d: ERROR - Match all cannot be combined with "
                              "other Match attributes", count);
                SAFE_FREE(x);
                return -1;
            case BIND_MATCH_USER:
            case BIND_MATCH_GROUP:
            case BIND_MATCH_HOST:
            case BIND_MATCH_LOCALADDRESS:
            case BIND_MATCH_LOCALPORT:
            case BIND_MATCH_RDOMAIN:
            case BIND_MATCH_ADDRESS:
                /* Only "All" is supported for now */
                /* Skip one argument */
                p = ssh_config_get_str_tok(&s, NULL);
                if (p == NULL || p[0] == '\0') {
                    SSH_LOG(SSH_LOG_TRACE, "line %d: Match keyword "
                            "'%s' requires argument\n", count, p2);
                    SAFE_FREE(x);
                    return -1;
                }
                args++;
                SSH_LOG(SSH_LOG_DEBUG,
                        "line %d: Unsupported Match keyword '%s', ignoring\n",
                        count,
                        p2);
                result = 0;
                break;
            case BIND_MATCH_UNKNOWN:
            default:
                ssh_set_error(bind, SSH_FATAL,
                              "ERROR - Unknown argument '%s' for Match keyword", p);
                SAFE_FREE(x);
                return -1;
            }
        } while (p != NULL && p[0] != '\0');
        if (args == 0) {
            ssh_set_error(bind, SSH_FATAL,
                          "ERROR - Match keyword requires an argument");
            SAFE_FREE(x);
            return -1;
        }
        /* This line only sets the PARSING flag if all checks passed */
        *parser_flags |= result;
        break;
    }
    case BIND_CFG_PUBKEY_ACCEPTED_KEY_TYPES:
        p = ssh_config_get_str_tok(&s, NULL);
        if (p && (*parser_flags & PARSING)) {
            rc = ssh_bind_options_set(bind,
                                 SSH_BIND_OPTIONS_PUBKEY_ACCEPTED_KEY_TYPES, p);
            if (rc != 0) {
                SSH_LOG(SSH_LOG_TRACE,
                        "line %d: Failed to set PubKeyAcceptedKeyTypes value '%s'",
                        count, p);
            }
        }
        break;
    case BIND_CFG_HOSTKEY_ALGORITHMS:
        p = ssh_config_get_str_tok(&s, NULL);
        if (p && (*parser_flags & PARSING)) {
            rc = ssh_bind_options_set(bind,
                                 SSH_BIND_OPTIONS_HOSTKEY_ALGORITHMS, p);
            if (rc != 0) {
                SSH_LOG(SSH_LOG_TRACE,
                        "line %d: Failed to set HostkeyAlgorithms value '%s'",
                        count, p);
            }
        }
        break;
    case BIND_CFG_NOT_ALLOWED_IN_MATCH:
        SSH_LOG(SSH_LOG_DEBUG, "Option not allowed in Match block: %s, line: %d",
                keyword, count);
        break;
    case BIND_CFG_UNKNOWN:
        SSH_LOG(SSH_LOG_TRACE, "Unknown option: %s, line: %d",
                keyword, count);
        break;
    case BIND_CFG_UNSUPPORTED:
        SSH_LOG(SSH_LOG_TRACE, "Unsupported option: %s, line: %d",
                keyword, count);
        break;
    case BIND_CFG_NA:
        SSH_LOG(SSH_LOG_TRACE, "Option not applicable: %s, line: %d",
                keyword, count);
        break;
    default:
        ssh_set_error(bind, SSH_FATAL, "ERROR - unimplemented opcode: %d",
                opcode);
        SAFE_FREE(x);
        return -1;
        break;
    }

    SAFE_FREE(x);
    return rc;
}

int ssh_bind_config_parse_file(ssh_bind bind, const char *filename)
{
    char line[MAX_LINE_SIZE] = {0};
    unsigned int count = 0;
    FILE *f = NULL;
    uint32_t parser_flags;
    int rv;

    /* This local table is used during the parsing of the current file (and
     * files included recursively in this file) to prevent an option to be
     * redefined, i.e. the first value set is kept. But this DO NOT prevent the
     * option to be redefined later by another file. */
    uint8_t seen[BIND_CFG_MAX] = {0};

    f = ssh_strict_fopen(filename, SSH_MAX_CONFIG_FILE_SIZE);
    if (f == NULL) {
        return 0;
    }

    SSH_LOG(SSH_LOG_PACKET, "Reading configuration data from %s", filename);

    parser_flags = PARSING;
    while (fgets(line, sizeof(line), f)) {
        count++;
        rv = ssh_bind_config_parse_line(bind, line, count, &parser_flags, seen, 0);
        if (rv) {
            fclose(f);
            return -1;
        }
    }

    fclose(f);
    return 0;
}

/* @brief Parse configuration string and set the options to the given bind session
 *
 * @params[in] bind      The ssh bind session
 * @params[in] input     Null terminated string containing the configuration
 *
 * @returns    SSH_OK on successful parsing the configuration string,
 *             SSH_ERROR on error
 */
int ssh_bind_config_parse_string(ssh_bind bind, const char *input)
{
    char line[MAX_LINE_SIZE] = {0};
    const char *c = input, *line_start = input;
    unsigned int line_num = 0, line_len;
    uint32_t parser_flags;
    int rv;

    /* This local table is used during the parsing of the current file (and
     * files included recursively in this file) to prevent an option to be
     * redefined, i.e. the first value set is kept. But this DO NOT prevent the
     * option to be redefined later by another file. */
    uint8_t seen[BIND_CFG_MAX] = {0};

    SSH_LOG(SSH_LOG_DEBUG, "Reading bind configuration data from string:");
    SSH_LOG(SSH_LOG_DEBUG, "START\n%s\nEND", input);

    parser_flags = PARSING;
    while (1) {
        line_num++;
        line_start = c;
        c = strchr(line_start, '\n');
        if (c == NULL) {
            /* if there is no newline at the end of the string */
            c = strchr(line_start, '\0');
        }
        if (c == NULL) {
            /* should not happen, would mean a string without trailing '\0' */
            SSH_LOG(SSH_LOG_WARN, "No trailing '\\0' in config string");
            return SSH_ERROR;
        }
        line_len = c - line_start;
        if (line_len > MAX_LINE_SIZE - 1) {
            SSH_LOG(SSH_LOG_WARN, "Line %u too long: %u characters",
                    line_num, line_len);
            return SSH_ERROR;
        }
        memcpy(line, line_start, line_len);
        line[line_len] = '\0';
        SSH_LOG(SSH_LOG_DEBUG, "Line %u: %s", line_num, line);
        rv = ssh_bind_config_parse_line(bind, line, line_num, &parser_flags, seen, 0);
        if (rv < 0) {
            return SSH_ERROR;
        }
        if (*c == '\0') {
            break;
        }
        c++;
    }

    return SSH_OK;
}