--- /dev/null
+From e5a0ef27c227f7ae69d9a9fec98a056494409b9b Mon Sep 17 00:00:00 2001
+From: Matt Johnston <matt@ucc.asn.au>
+Date: Mon, 5 May 2025 23:14:19 +0800
+Subject: [PATCH] Execute multihop commands directly, no shell
+
+This avoids problems with shell escaping if arguments contain special
+characters.
+
+CVE: CVE-2025-47203
+Upstream-Status: Backport [https://github.com/mkj/dropbear/commit/e5a0ef27c227f7ae69d9a9fec98a056494409b9b]
+Signed-off-by: Peter Marko <peter.marko@siemens.com>
+---
+ src/cli-main.c | 59 +++++++++++++++++---------
+ src/cli-runopts.c | 104 ++++++++++++++++++++++++++++------------------
+ src/dbutil.c | 9 +++-
+ src/dbutil.h | 1 +
+ src/runopts.h | 5 +++
+ 5 files changed, 117 insertions(+), 61 deletions(-)
+
+diff --git a/src/cli-main.c b/src/cli-main.c
+index 065fd76..2fafa88 100644
+--- a/src/cli-main.c
++++ b/src/cli-main.c
+@@ -77,9 +77,8 @@ int main(int argc, char ** argv) {
+ }
+
+ #if DROPBEAR_CLI_PROXYCMD
+- if (cli_opts.proxycmd) {
++ if (cli_opts.proxycmd || cli_opts.proxyexec) {
+ cli_proxy_cmd(&sock_in, &sock_out, &proxy_cmd_pid);
+- m_free(cli_opts.proxycmd);
+ if (signal(SIGINT, kill_proxy_sighandler) == SIG_ERR ||
+ signal(SIGTERM, kill_proxy_sighandler) == SIG_ERR ||
+ signal(SIGHUP, kill_proxy_sighandler) == SIG_ERR) {
+@@ -101,7 +100,8 @@ int main(int argc, char ** argv) {
+ }
+ #endif /* DBMULTI stuff */
+
+-static void exec_proxy_cmd(const void *user_data_cmd) {
++#if DROPBEAR_CLI_PROXYCMD
++static void shell_proxy_cmd(const void *user_data_cmd) {
+ const char *cmd = user_data_cmd;
+ char *usershell;
+
+@@ -110,41 +110,62 @@ static void exec_proxy_cmd(const void *user_data_cmd) {
+ dropbear_exit("Failed to run '%s'\n", cmd);
+ }
+
+-#if DROPBEAR_CLI_PROXYCMD
++static void exec_proxy_cmd(const void *unused) {
++ (void)unused;
++ run_command(cli_opts.proxyexec[0], cli_opts.proxyexec, ses.maxfd);
++ dropbear_exit("Failed to run '%s'\n", cli_opts.proxyexec[0]);
++}
++
+ static void cli_proxy_cmd(int *sock_in, int *sock_out, pid_t *pid_out) {
+- char * ex_cmd = NULL;
+- size_t ex_cmdlen;
++ char * cmd_arg = NULL;
++ void (*exec_fn)(const void *user_data) = NULL;
+ int ret;
+
++ /* exactly one of cli_opts.proxycmd or cli_opts.proxyexec should be set */
++
+ /* File descriptor "-j &3" */
+- if (*cli_opts.proxycmd == '&') {
++ if (cli_opts.proxycmd && *cli_opts.proxycmd == '&') {
+ char *p = cli_opts.proxycmd + 1;
+ int sock = strtoul(p, &p, 10);
+ /* must be a single number, and not stdin/stdout/stderr */
+ if (sock > 2 && sock < 1024 && *p == '\0') {
+ *sock_in = sock;
+ *sock_out = sock;
+- return;
++ goto cleanup;
+ }
+ }
+
+- /* Normal proxycommand */
++ if (cli_opts.proxycmd) {
++ /* Normal proxycommand */
++ size_t shell_cmdlen;
++ /* So that spawn_command knows which shell to run */
++ fill_passwd(cli_opts.own_user);
+
+- /* So that spawn_command knows which shell to run */
+- fill_passwd(cli_opts.own_user);
++ shell_cmdlen = strlen(cli_opts.proxycmd) + 6; /* "exec " + command + '\0' */
++ cmd_arg = m_malloc(shell_cmdlen);
++ snprintf(cmd_arg, shell_cmdlen, "exec %s", cli_opts.proxycmd);
++ exec_fn = shell_proxy_cmd;
++ } else {
++ /* No shell */
++ exec_fn = exec_proxy_cmd;
++ }
+
+- ex_cmdlen = strlen(cli_opts.proxycmd) + 6; /* "exec " + command + '\0' */
+- ex_cmd = m_malloc(ex_cmdlen);
+- snprintf(ex_cmd, ex_cmdlen, "exec %s", cli_opts.proxycmd);
+-
+- ret = spawn_command(exec_proxy_cmd, ex_cmd,
+- sock_out, sock_in, NULL, pid_out);
+- DEBUG1(("cmd: %s pid=%d", ex_cmd,*pid_out))
+- m_free(ex_cmd);
++ ret = spawn_command(exec_fn, cmd_arg, sock_out, sock_in, NULL, pid_out);
+ if (ret == DROPBEAR_FAILURE) {
+ dropbear_exit("Failed running proxy command");
+ *sock_in = *sock_out = -1;
+ }
++
++cleanup:
++ m_free(cli_opts.proxycmd);
++ m_free(cmd_arg);
++ if (cli_opts.proxyexec) {
++ char **a = NULL;
++ for (a = cli_opts.proxyexec; *a; a++) {
++ m_free_direct(*a);
++ }
++ m_free(cli_opts.proxyexec);
++ }
+ }
+
+ static void kill_proxy_sighandler(int UNUSED(signo)) {
+diff --git a/src/cli-runopts.c b/src/cli-runopts.c
+index b664293..a21b7a2 100644
+--- a/src/cli-runopts.c
++++ b/src/cli-runopts.c
+@@ -556,62 +556,88 @@ void loadidentityfile(const char* filename, int warnfail) {
+
+ /* Fill out -i, -y, -W options that make sense for all
+ * the intermediate processes */
+-static char* multihop_passthrough_args(void) {
+- char *args = NULL;
+- unsigned int len, total;
++static char** multihop_args(const char* argv0, const char* prior_hops) {
++ /* null terminated array */
++ char **args = NULL;
++ size_t max_args = 14, pos = 0, len;
+ #if DROPBEAR_CLI_PUBKEY_AUTH
+ m_list_elem *iter;
+ #endif
+- /* Sufficient space for non-string args */
+- len = 100;
+
+- /* String arguments have arbitrary length, so determine space required */
+- if (cli_opts.proxycmd) {
+- len += strlen(cli_opts.proxycmd);
+- }
+ #if DROPBEAR_CLI_PUBKEY_AUTH
+ for (iter = cli_opts.privkeys->first; iter; iter = iter->next)
+ {
+- sign_key * key = (sign_key*)iter->item;
+- len += 4 + strlen(key->filename);
++ /* "-i file" for each */
++ max_args += 2;
+ }
+ #endif
+
+- args = m_malloc(len);
+- total = 0;
++ args = m_malloc(sizeof(char*) * max_args);
++ pos = 0;
+
+- /* Create new argument string */
++ args[pos] = m_strdup(argv0);
++ pos++;
+
+ if (cli_opts.quiet) {
+- total += m_snprintf(args+total, len-total, "-q ");
++ args[pos] = m_strdup("-q");
++ pos++;
+ }
+
+ if (cli_opts.no_hostkey_check) {
+- total += m_snprintf(args+total, len-total, "-y -y ");
++ args[pos] = m_strdup("-y");
++ pos++;
++ args[pos] = m_strdup("-y");
++ pos++;
+ } else if (cli_opts.always_accept_key) {
+- total += m_snprintf(args+total, len-total, "-y ");
++ args[pos] = m_strdup("-y");
++ pos++;
+ }
+
+ if (cli_opts.batch_mode) {
+- total += m_snprintf(args+total, len-total, "-o BatchMode=yes ");
++ args[pos] = m_strdup("-o");
++ pos++;
++ args[pos] = m_strdup("BatchMode=yes");
++ pos++;
+ }
+
+ if (cli_opts.proxycmd) {
+- total += m_snprintf(args+total, len-total, "-J '%s' ", cli_opts.proxycmd);
++ args[pos] = m_strdup("-J");
++ pos++;
++ args[pos] = m_strdup(cli_opts.proxycmd);
++ pos++;
+ }
+
+ if (opts.recv_window != DEFAULT_RECV_WINDOW) {
+- total += m_snprintf(args+total, len-total, "-W %u ", opts.recv_window);
++ args[pos] = m_strdup("-W");
++ pos++;
++ args[pos] = m_malloc(11);
++ m_snprintf(args[pos], 11, "%u", opts.recv_window);
++ pos++;
+ }
+
+ #if DROPBEAR_CLI_PUBKEY_AUTH
+ for (iter = cli_opts.privkeys->first; iter; iter = iter->next)
+ {
+ sign_key * key = (sign_key*)iter->item;
+- total += m_snprintf(args+total, len-total, "-i %s ", key->filename);
++ args[pos] = m_strdup("-i");
++ pos++;
++ args[pos] = m_strdup(key->filename);
++ pos++;
+ }
+ #endif /* DROPBEAR_CLI_PUBKEY_AUTH */
+
++ /* last hop */
++ args[pos] = m_strdup("-B");
++ pos++;
++ len = strlen(cli_opts.remotehost) + strlen(cli_opts.remoteport) + 2;
++ args[pos] = m_malloc(len);
++ snprintf(args[pos], len, "%s:%s", cli_opts.remotehost, cli_opts.remoteport);
++ pos++;
++
++ /* hostnames of prior hops */
++ args[pos] = m_strdup(prior_hops);
++ pos++;
++
+ return args;
+ }
+
+@@ -626,7 +652,7 @@ static char* multihop_passthrough_args(void) {
+ * etc for as many hosts as we want.
+ *
+ * Note that "-J" arguments aren't actually used, instead
+- * below sets cli_opts.proxycmd directly.
++ * below sets cli_opts.proxyexec directly.
+ *
+ * Ports for hosts can be specified as host/port.
+ */
+@@ -634,7 +660,7 @@ static void parse_multihop_hostname(const char* orighostarg, const char* argv0)
+ char *userhostarg = NULL;
+ char *hostbuf = NULL;
+ char *last_hop = NULL;
+- char *remainder = NULL;
++ char *prior_hops = NULL;
+
+ /* both scp and rsync parse a user@host argument
+ * and turn it into "-l user host". This breaks
+@@ -652,6 +678,8 @@ static void parse_multihop_hostname(const char* orighostarg, const char* argv0)
+ }
+ userhostarg = hostbuf;
+
++ /* Split off any last hostname and use that as remotehost/remoteport.
++ * That is used for authorized_keys checking etc */
+ last_hop = strrchr(userhostarg, ',');
+ if (last_hop) {
+ if (last_hop == userhostarg) {
+@@ -659,32 +687,28 @@ static void parse_multihop_hostname(const char* orighostarg, const char* argv0)
+ }
+ *last_hop = '\0';
+ last_hop++;
+- remainder = userhostarg;
++ prior_hops = userhostarg;
+ userhostarg = last_hop;
+ }
+
++ /* Update cli_opts.remotehost and cli_opts.remoteport */
+ parse_hostname(userhostarg);
+
+- if (last_hop) {
+- /* Set up the proxycmd */
+- unsigned int cmd_len = 0;
+- char *passthrough_args = multihop_passthrough_args();
+- cmd_len = strlen(argv0) + strlen(remainder)
+- + strlen(cli_opts.remotehost) + strlen(cli_opts.remoteport)
+- + strlen(passthrough_args)
+- + 30;
+- /* replace proxycmd. old -J arguments have been copied
+- to passthrough_args */
+- cli_opts.proxycmd = m_realloc(cli_opts.proxycmd, cmd_len);
+- m_snprintf(cli_opts.proxycmd, cmd_len, "%s -B %s:%s %s %s",
+- argv0, cli_opts.remotehost, cli_opts.remoteport,
+- passthrough_args, remainder);
++ /* Construct any multihop proxy command. Use proxyexec to
++ * avoid worrying about shell escaping. */
++ if (prior_hops) {
++ cli_opts.proxyexec = multihop_args(argv0, prior_hops);
++ /* Any -J argument has been copied to proxyexec */
++ if (cli_opts.proxycmd) {
++ m_free(cli_opts.proxycmd);
++ }
++
+ #ifndef DISABLE_ZLIB
+- /* The stream will be incompressible since it's encrypted. */
++ /* This outer stream will be incompressible since it's encrypted. */
+ opts.compress_mode = DROPBEAR_COMPRESS_OFF;
+ #endif
+- m_free(passthrough_args);
+ }
++
+ m_free(hostbuf);
+ }
+ #endif /* DROPBEAR_CLI_MULTIHOP */
+diff --git a/src/dbutil.c b/src/dbutil.c
+index 2b44921..a70025e 100644
+--- a/src/dbutil.c
++++ b/src/dbutil.c
+@@ -371,7 +371,6 @@ int spawn_command(void(*exec_fn)(const void *user_data), const void *exec_data,
+ void run_shell_command(const char* cmd, unsigned int maxfd, char* usershell) {
+ char * argv[4];
+ char * baseshell = NULL;
+- unsigned int i;
+
+ baseshell = basename(usershell);
+
+@@ -393,6 +392,12 @@ void run_shell_command(const char* cmd, unsigned int maxfd, char* usershell) {
+ argv[1] = NULL;
+ }
+
++ run_command(usershell, argv, maxfd);
++}
++
++void run_command(const char* argv0, char** args, unsigned int maxfd) {
++ unsigned int i;
++
+ /* Re-enable SIGPIPE for the executed process */
+ if (signal(SIGPIPE, SIG_DFL) == SIG_ERR) {
+ dropbear_exit("signal() error");
+@@ -404,7 +409,7 @@ void run_shell_command(const char* cmd, unsigned int maxfd, char* usershell) {
+ m_close(i);
+ }
+
+- execv(usershell, argv);
++ execv(argv0, args);
+ }
+
+ #if DEBUG_TRACE
+diff --git a/src/dbutil.h b/src/dbutil.h
+index 05fc50c..bfbed73 100644
+--- a/src/dbutil.h
++++ b/src/dbutil.h
+@@ -63,6 +63,7 @@ char * stripcontrol(const char * text);
+ int spawn_command(void(*exec_fn)(const void *user_data), const void *exec_data,
+ int *writefd, int *readfd, int *errfd, pid_t *pid);
+ void run_shell_command(const char* cmd, unsigned int maxfd, char* usershell);
++void run_command(const char* argv0, char** args, unsigned int maxfd);
+ #if ENABLE_CONNECT_UNIX
+ int connect_unix(const char* addr);
+ #endif
+diff --git a/src/runopts.h b/src/runopts.h
+index c4061a0..f255882 100644
+--- a/src/runopts.h
++++ b/src/runopts.h
+@@ -197,7 +197,12 @@ typedef struct cli_runopts {
+ unsigned int netcat_port;
+ #endif
+ #if DROPBEAR_CLI_PROXYCMD
++ /* A proxy command to run via the user's shell */
+ char *proxycmd;
++#endif
++#if DROPBEAR_CLI_MULTIHOP
++ /* Similar to proxycmd, but is arguments for execve(), not shell */
++ char **proxyexec;
+ #endif
+ const char *bind_arg;
+ char *bind_address;
projects / thirdparty / openembedded / openembedded-core.git / commitdiff
