misc-progs: Introduce run()

This function invokes a new command similar to safe_system()
but without launching a shell before.

That way, it is possible to execute commands without any risk
of shell command injection from nobody.

Fixes: #12562
Reported-by: Albert Schwarzkopf <ipfire@quitesimple.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

diff --git a/src/misc-progs/setuid.c b/src/misc-progs/setuid.c
index e54b5d3abe7b66e20e76f6cc66cd91db1fab8ac8..6637d3e6fcba82bc40acd27a62160d57e2c0544e 100644 (file)
--- a/src/misc-progs/setuid.c
+++ b/src/misc-progs/setuid.c
@@ -20,6 +20,7 @@
  *
  */
 
+#include <ctype.h>
 #include <stdio.h>
 #include <string.h>
 #include <errno.h>
@@ -41,6 +42,8 @@
 #define OPEN_MAX 256
 #endif
 
+#define MAX_ARGUMENTS 128
+
 /* Trusted environment for executing commands */
 char * trusted_env[4] = {
        "PATH=/usr/bin:/usr/sbin:/sbin:/bin",
@@ -49,37 +52,40 @@ char * trusted_env[4] = {
        NULL
 };
 
-/* Spawns a child process that uses /bin/sh to interpret a command.
- * This is much the same in use and purpose as system(), yet as it uses execve
- * to pass a trusted environment it's immune to attacks based upon changing
- * IFS, ENV, BASH_ENV and other such variables.
- * Note this does NOT guard against any other attacks, inparticular you MUST
- * validate the command you are passing. If the command is formed from user
- * input be sure to check this input is what you expect. Nasty things can
- * happen if a user can inject ; or `` into your command for example */
-int safe_system(char* command) {
-       return system_core(command, 0, 0, "safe_system");
-}
-
-/* Much like safe_system but lets you specify a non-root uid and gid to run
- * the command as */
-int unpriv_system(char* command, uid_t uid, gid_t gid) {
-       return system_core(command, uid, gid, "unpriv_system");
-}
-
-int system_core(char* command, uid_t uid, gid_t gid, char *error) {
+static int system_core(char* command, char** args, uid_t uid, gid_t gid, char *error) {
        int pid, status;
 
+       char* argv[MAX_ARGUMENTS + 1];
+       unsigned int argc = 0;
+
        if(!command)
                return 1;
 
+#if 0
+       // Add command as first element to argv
+       argv[argc++] = command;
+#endif
+
+       // Add all other arguments
+       if (args) {
+               while (*args) {
+                       argv[argc++] = *args++;
+
+                       // Break when argv is full
+                       if (argc >= MAX_ARGUMENTS) {
+                               return 2;
+                       }
+               }
+       }
+
+       // Make sure that argv is NULL-terminated
+       argv[argc] = NULL;
+
        switch(pid = fork()) {
                case -1:
                        return -1;
 
                case 0: /* child */ {
-                       char *argv[4];
-
                        if (gid && setgid(gid)) {
                                fprintf(stderr, "%s: ", error);
                                perror("Couldn't setgid");
@@ -92,11 +98,8 @@ int system_core(char* command, uid_t uid, gid_t gid, char *error) {
                                exit(127);
                        }
 
-                       argv[0] = "sh";
-                       argv[1] = "-c";
-                       argv[2] = command;
-                       argv[3] = NULL;
-                       execve("/bin/sh", argv, trusted_env);
+                       execve(command, argv, trusted_env);
+
                        fprintf(stderr, "%s: ", error);
                        perror("execve failed");
                        exit(127);
@@ -115,6 +118,35 @@ int system_core(char* command, uid_t uid, gid_t gid, char *error) {
 
 }
 
+int run(char* command, char** argv) {
+       return system_core(command, argv, 0, 0, "run");
+}
+
+/* Spawns a child process that uses /bin/sh to interpret a command.
+ * This is much the same in use and purpose as system(), yet as it uses execve
+ * to pass a trusted environment it's immune to attacks based upon changing
+ * IFS, ENV, BASH_ENV and other such variables.
+ * Note this does NOT guard against any other attacks, inparticular you MUST
+ * validate the command you are passing. If the command is formed from user
+ * input be sure to check this input is what you expect. Nasty things can
+ * happen if a user can inject ; or `` into your command for example */
+int safe_system(char* command) {
+       char* argv[4] = {
+               "/bin/sh",
+               "-c",
+               command,
+               NULL,
+       };
+
+       return system_core(argv[0], argv, 0, 0, "safe_system");
+}
+
+/* Much like safe_system but lets you specify a non-root uid and gid to run
+ * the command as */
+int unpriv_system(char* command, uid_t uid, gid_t gid) {
+       return system_core(command, NULL, uid, gid, "unpriv_system");
+}
+
 /* General routine to initialise a setuid root program, and put the
  * environment in a known state. Returns 1 on success, if initsetuid() returns
  * 0 then you should exit(1) immediately, DON'T attempt to recover from the

diff --git a/src/misc-progs/setuid.h b/src/misc-progs/setuid.h
index 7f3fda30808c6d40c6af8cf637ff20bf7b5ef4f6..aa265a52f7c31e8f2304f3f2f99411584c759af7 100644 (file)
--- a/src/misc-progs/setuid.h
+++ b/src/misc-progs/setuid.h
@@ -28,7 +28,7 @@
 
 extern char * trusted_env[4];
 
-int system_core(char* command, uid_t uid, gid_t gid, char *error);
+int run(char* command, char** argv);
 int safe_system(char* command);
 int unpriv_system(char* command, uid_t uid, gid_t gid);
 int initsetuid(void);