tinyproxy · tkluck · Mar 1, 2019 · Mar 1, 2019
diff --git a/configure.ac b/configure.ac
@@ -134,7 +134,7 @@ AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK
 AC_FUNC_MALLOC
 AC_FUNC_REALLOC
 
-AC_CHECK_FUNCS([inet_ntoa strdup])
+AC_CHECK_FUNCS([inet_ntoa strdup fdopen])
 AC_CHECK_FUNCS([strlcpy strlcat setgroups])
 
 dnl Enable extra warnings

diff --git a/src/Makefile.am b/src/Makefile.am
@@ -46,6 +46,7 @@ tinyproxy_SOURCES = \
 	utils.c utils.h \
 	vector.c vector.h \
 	upstream.c upstream.h \
+	upstream-command.c upstream-command.h \
 	basicauth.c basicauth.h \
 	base64.c base64.h \
 	connect-ports.c connect-ports.h

diff --git a/src/conf.c b/src/conf.c
@@ -165,6 +165,7 @@ static HANDLE_FUNC (handle_xtinyproxy);
 #ifdef UPSTREAM_SUPPORT
 static HANDLE_FUNC (handle_upstream);
 static HANDLE_FUNC (handle_upstream_no);
+static HANDLE_FUNC (handle_upstream_command);
 #endif
 
 static void config_free_regex (void);
@@ -264,6 +265,12 @@ struct {
                       ":" INT "(" WS STR ")?"
                 END, handle_upstream, NULL
         },
+        {
+                BEGIN "(upstream)" WS "(command)" WS
+                      STR /* path to script */
+                      "(" WS STR ")?" /* host filter */
+                END, handle_upstream_command, NULL
+        },
 #endif
         /* loglevel */
         STDCONF ("loglevel", "(critical|error|warning|notice|connect|info)",
@@ -1135,7 +1142,7 @@ static HANDLE_FUNC (handle_upstream)
         if (match[mi].rm_so != -1)
                 domain = get_string_arg (line, &match[mi]);
 
-        upstream_add (ip, port, domain, user, pass, pt, &conf->upstream_list);
+        upstream_add (ip, port, domain, user, pass, NULL, pt, &conf->upstream_list);
 
         safefree (user);
         safefree (pass);
@@ -1153,9 +1160,31 @@ static HANDLE_FUNC (handle_upstream_no)
         if (!domain)
                 return -1;
 
-        upstream_add (NULL, 0, domain, 0, 0, PT_NONE, &conf->upstream_list);
+        upstream_add (NULL, 0, domain, 0, 0, NULL, PT_NONE, &conf->upstream_list);
         safefree (domain);
 
         return 0;
 }
-#endif
+
+static HANDLE_FUNC (handle_upstream_command)
+{
+        int mi = 3;
+        char *command = 0, *domain = 0;
+
+        command = get_string_arg (line, &match[mi]);
+        mi++;
+
+        if (match[mi].rm_so != -1)
+                domain = get_string_arg (line, &match[mi]);
+        mi++;
+
+        upstream_add (NULL, 0, domain, 0, 0, command, PT_NONE, &conf->upstream_list);
+
+        safefree (command);
+        safefree (domain);
+
+        return 0;
+}
+
+
+#endif /* UPSTREAM_SUPPORT */
diff --git a/src/upstream-command.c b/src/upstream-command.c
@@ -0,0 +1,140 @@
+/* TODO(tkluck): this is needed for fdopen. Does it have portability
+ * downsides? */
+#define _POSIX_C_SOURCE 1
+#include <stdio.h>
+
+#include "upstream-command.h"
+#include "upstream.h"
+
+#define MAX_RESULT_MESSAGE_SIZE 1024
+
+/*
+ * ensure that st->in is writable (according to select() ). Use select()
+ * to wait at most UPSTREAM_COMMAND_WRITABLE_TIMOUT_MS milliseconds,
+ * and respawn otherwise.
+ * Returns a negative error code if we do not succeed in respawning.
+ */
+static int ensure_upstream_command_writable(const char *cmd, struct upstream_command_state *st)
+{
+        int err;
+        int parent2child[2];
+        int child2parent[2];
+
+        assert(st != NULL);
+
+        if (0 == st->pid) {
+                err = pipe(parent2child);
+                if (0 != err)
+                        return -1;
+                err = pipe(child2parent);
+                if (0 != err)
+                        return -1;
+
+                st->pid = fork();
+                if (0 > st->pid)
+                        return -1;
+                if (0 == st->pid) {
+                        /* I'm the child; connect stdin/stdout to the pipes */
+                        if (0 > close(parent2child[1]))
+                                exit(1);
+                        if (0 > close(child2parent[0]))
+                                exit(1);
+                        if (0 > dup2(parent2child[0], 0))
+                                exit(1);
+                        if (0 > dup2(child2parent[1], 1))
+                                exit(1);
+
+                        /* TODO(tkluck): do we need to worry about installed
+                         * signal handlers (e.g. for SIGCHLD)?
+                         */
+
+                        err = execl("/bin/sh", "sh", "-c", cmd, (char *) 0);
+
+                        /* unreachable unless something is wrong with the command */
+                        exit(1);
+                } else {
+                        /* I'm the parent */
+                        sleep(1);
+                        close(parent2child[0]);
+                        close(child2parent[1]);
+                        st->in  = fdopen(parent2child[1], "w");
+                        st->out = fdopen(child2parent[0], "r");
+                }
+        }
+
+        /* TODO(tkluck): use select(2) to ensure that writing to
+         * the process stdin doesn't block (for sufficiently small
+         * message). Otherwise, fork a new copy and kill the old one. */
+
+        return 0;
+}
+
+/*
+ * Communicate with the configured command to obtain a proxy
+ * specification, and _replace_ the fields in *up with the appropriate
+ * spec.
+ *
+ * In case of success, returns one of the following positive constants:
+ *     UPSTREAM_DIRECT - no proxy
+ *     UPSTREAM_FALLTHROUGH - use subsequent rules
+ *     UPSTREAM_PROXY - use upstream as configured in *up
+ *
+ * Returns a negative error code if we do not succeed in communicating
+ * with the subprocess.
+ */
+int upstream_get_from_command(const char *host, struct upstream *up)
+{
+        int err;
+        char msg[MAX_RESULT_MESSAGE_SIZE];
+        char *msgres;
+
+        assert(up != NULL);
+        assert(up->command != NULL);
+        if (NULL != strchr(host, '\n'))
+                return -1;
+
+        err = ensure_upstream_command_writable(up->command, &up->cmdstate);
+        if (err < 0)
+                return -2;
+
+        /* TODO(tkluck): replace by version with timeout. */
+        err = fprintf(up->cmdstate.in, "HOST %s\n", host);
+        if (err < 0)
+                return -3;
+        err = fflush(up->cmdstate.in);
+        if (err != 0)
+                return -4;
+
+        /* TODO(tkluck): replace by version with timeout */
+        msgres = fgets(msg, MAX_RESULT_MESSAGE_SIZE, up->cmdstate.out);
+        if (NULL == msgres)
+                return -5;
+
+        if (strncmp(msg, "DIRECT",       6)) {
+                return UPSTREAM_DIRECT;
+        } else if
+           (strncmp(msg, "FALLTHROUGH", 11)) {
+                return UPSTREAM_FALLTHROUGH;
+        } else if
+           (strncmp(msg, "HTTP ",        5)) {
+                /* TODO(tkluck): parse and fill the struct here.
+                 * use same/similar format as the configuration file */
+                return UPSTREAM_PROXY;
+        } else if
+           (strncmp(msg, "SOCKS4 ",      7)) {
+                /* TODO(tkluck): parse and fill the struct here.
+                 * use same/similar format as the configuration file */
+                return UPSTREAM_PROXY;
+        } else if
+           (strncmp(msg, "SOCKS5 ",      7)) {
+                /* TODO(tkluck): parse and fill the struct here.
+                 * use same/similar format as the configuration file */
+                return UPSTREAM_PROXY;
+        } else {
+                goto parsefail;
+        }
+
+parsefail:
+        return -6;
+
+}
diff --git a/src/upstream-command.h b/src/upstream-command.h
@@ -0,0 +1,19 @@
+#ifndef _TINYPROXY_UPSTREAM_COMMAND_H_
+#define _TINYPROXY_UPSTREAM_COMMAND_H_
+
+#include <stdio.h>
+
+typedef enum upstream_command_result {
+  UPSTREAM_DIRECT = 1,
+  UPSTREAM_FALLTHROUGH,
+  UPSTREAM_PROXY,
+} upstream_command_result;
+
+struct upstream_command_state {
+        int pid;
+        FILE *in;
+        FILE *out;
+};
+
+
+#endif /* _TINYPROXY_UPSTREAM_COMMAND_H_ */
diff --git a/src/upstream.c b/src/upstream.c
@@ -47,7 +47,7 @@ proxy_type_name(proxy_type type)
  * Construct an upstream struct from input data.
  */
 static struct upstream *upstream_build (const char *host, int port, const char *domain,
-                        const char *user, const char *pass,
+                        const char *user, const char *pass, const char *command,
 			proxy_type type)
 {
         char *ptr;
@@ -63,6 +63,9 @@ static struct upstream *upstream_build (const char *host, int port, const char *
         up->type = type;
         up->host = up->domain = up->ua.user = up->pass = NULL;
         up->ip = up->mask = 0;
+        up->command = NULL;
+        up->cmdstate.in = up->cmdstate.out = NULL;
+        up->cmdstate.pid = 0;
         if (user) {
                 if (type == PT_HTTP) {
                         char b[BASE64ENC_BYTES((256+2)-1) + 1];
@@ -80,6 +83,21 @@ static struct upstream *upstream_build (const char *host, int port, const char *
                 }
         }
 
+        if (command) {
+                up->command = safestrdup(command);
+                if (domain && domain[0] != '\0')
+                        up->domain = safestrdup (domain);
+
+                if (domain && domain[0] != '\0') {
+                        log_message (LOG_INFO, "Added upstream command %s for %s",
+                                     up->command, up->domain);
+                } else {
+                        log_message (LOG_INFO, "Added upstream command %s",
+                                     up->command);
+                }
+                return up;
+        }
+
         if (domain == NULL) {
                 if (!host || host[0] == '\0' || port < 1) {
                         log_message (LOG_WARNING,
@@ -154,12 +172,12 @@ static struct upstream *upstream_build (const char *host, int port, const char *
  * Add an entry to the upstream list
  */
 void upstream_add (const char *host, int port, const char *domain,
-                   const char *user, const char *pass,
+                   const char *user, const char *pass, const char *command,
                    proxy_type type, struct upstream **upstream_list)
 {
         struct upstream *up;
 
-        up = upstream_build (host, port, domain, user, pass, type);
+        up = upstream_build (host, port, domain, user, pass, command, type);
         if (up == NULL) {
                 return;
         }
@@ -203,32 +221,58 @@ void upstream_add (const char *host, int port, const char *domain,
 struct upstream *upstream_get (char *host, struct upstream *up)
 {
         in_addr_t my_ip = INADDR_NONE;
+        int maskfail;
+        int res;
 
         while (up) {
+                maskfail = (up->domain || up->ip) ? 1 : 0;
                 if (up->domain) {
                         if (strcasecmp (host, up->domain) == 0)
-                                break;  /* exact match */
+                                maskfail = 0;  /* exact match */
 
                         if (up->domain[0] == '.') {
                                 char *dot = strchr (host, '.');
 
                                 if (!dot && !up->domain[1])
-                                        break;  /* local host matches "." */
+                                        maskfail = 0;  /* local host matches "." */
 
                                 while (dot && strcasecmp (dot, up->domain))
                                         dot = strchr (dot + 1, '.');
 
                                 if (dot)
-                                        break;  /* subdomain match */
+                                        maskfail = 0;  /* subdomain match */
                         }
                 } else if (up->ip) {
                         if (my_ip == INADDR_NONE)
                                 my_ip = ntohl (inet_addr (host));
 
                         if ((my_ip & up->mask) == up->ip)
+                                maskfail = 0;
+                }
+
+                if (!maskfail) {
+                        if (!up->command)
+                               break;
+
+                        log_message (LOG_INFO,
+                                     "Running command %s for host %s",
+                                     up->command, host);
+                        res = upstream_get_from_command(host, up);
+                        if (UPSTREAM_DIRECT == res || UPSTREAM_PROXY == res) {
                                 break;
-                } else {
-                        break;  /* No domain or IP, default upstream */
+                        } else if (UPSTREAM_FALLTHROUGH == res) {
+                                /* continue */
+                        } else {
+                                /* command failure
+                                 * TODO(tkluck): we should propagate this failure
+                                 * and reject the request rather than forwarding
+                                 * the request to a 'random' location. E.g. if
+                                 * the user configures a proxy for privacy reasons,
+                                 * command failure should not compromise their
+                                 * privacy.
+                                 */
+                                return NULL;
+                        }
                 }
 
                 up = up->next;
@@ -251,6 +295,7 @@ void free_upstream_list (struct upstream *up)
         while (up) {
                 struct upstream *tmp = up;
                 up = up->next;
+                safefree (tmp->command);
                 safefree (tmp->domain);
                 safefree (tmp->host);
                 safefree (tmp);

diff --git a/src/upstream.h b/src/upstream.h
@@ -26,6 +26,7 @@
 #define _TINYPROXY_UPSTREAM_H_
 
 #include "common.h"
+#include "upstream-command.h"
 
 /*
  * Even if upstream support is not compiled into tinyproxy, this
@@ -50,15 +51,19 @@ struct upstream {
         int port;
         in_addr_t ip, mask;
         proxy_type type;
+        char *command;
+        struct upstream_command_state cmdstate;
 };
 
 #ifdef UPSTREAM_SUPPORT
 const char *proxy_type_name(proxy_type type);
 extern void upstream_add (const char *host, int port, const char *domain,
                           const char *user, const char *pass,
+                          const char *command,
                           proxy_type type, struct upstream **upstream_list);
 extern struct upstream *upstream_get (char *host, struct upstream *up);
 extern void free_upstream_list (struct upstream *up);
+int upstream_get_from_command(const char *host, struct upstream *up);
 #endif /* UPSTREAM_SUPPORT */
 
 #endif /* _TINYPROXY_UPSTREAM_H_ */