2 files changed, 126 insertions, 0 deletions
diff --git a/pinyweb/suid/Makefile b/pinyweb/suid/Makefile
new file mode 100644
index 0000000..6d67058
--- /dev/null
+++ b/pinyweb/suid/Makefile
@@ -0,0 +1,5 @@
+piny-suid: piny-suid.c
+	gcc -Wall -Werror -Os -o $@ $<
+
+clean:
+	rm -f piny-suid
diff --git a/pinyweb/suid/piny-suid.c b/pinyweb/suid/piny-suid.c
new file mode 100644
index 0000000..251e3e1
--- /dev/null
+++ b/pinyweb/suid/piny-suid.c
@@ -0,0 +1,121 @@
+#include <errno.h>
+#include <pwd.h>
+#include <regex.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/types.h>
+#include <syslog.h>
+#include <unistd.h>
+
+int main( int argc, char *argv[] ) {
+
+  int err;
+
+  openlog( "piny-suid", LOG_ODELAY, LOG_AUTHPRIV );
+
+  if ( argc < 3 ) {
+    syslog( LOG_ERR, "Invalid usage" );
+    fprintf( stderr, "Usage: %s username command [args ...]\n", argv[0] );
+    return 1;
+  };
+
+  regex_t user_reg;
+
+  // Please note that these regular expressions should duplicate the language for usernames described in Piny::User.
+  if ( ( err = regcomp( &user_reg, "^[a-zA-Z][a-zA-Z0-9_.-]*$", REG_EXTENDED | REG_NOSUB ) ) != 0 ) {
+    size_t sz = regerror( err, &user_reg, NULL, 0 );
+    char buf[sz];
+    regerror( err, &user_reg, buf, sz );
+    syslog( LOG_CRIT, "Internal error; first regex, %s", buf );
+    fprintf( stderr, "Internal error compiling first regular expression: %s\n", buf );
+    return 1;
+  };
+
+  if ( regexec( &user_reg, argv[1], 0, NULL, 0 ) ) {
+    syslog( LOG_ERR, "Invalid username '%s' (first regex)", argv[1] );
+    fprintf( stderr, "'%s' does not appear to be a valid username!\n", argv[1] );
+    return 1;
+  };
+
+  regfree( &user_reg );
+
+  if ( ( err = regcomp( &user_reg, "^(git|ikiwiki)-", REG_EXTENDED | REG_NOSUB ) ) != 0 ) {
+    size_t sz = regerror( err, &user_reg, NULL, 0 );
+    char buf[sz];
+    regerror( err, &user_reg, buf, sz );
+    syslog( LOG_CRIT, "Internal error: second regex, %s", buf );
+    fprintf( stderr, "Internal error compiling second regular expression: %s\n", buf );
+    return 1;
+  };
+
+  if ( ! regexec( &user_reg, argv[1], 0, NULL, 0 ) ) {
+    syslog( LOG_ERR, "Invalid username '%s' (second regex)", argv[1] );
+    fprintf( stderr, "'%s' does not appear to be a valid username!\n", argv[1] );
+    return 1;
+  };
+
+  regfree( &user_reg );
+
+  regex_t cmd_reg;
+
+  if ( ( err = regcomp( &cmd_reg, "/", REG_EXTENDED | REG_NOSUB ) ) != 0 ) {
+    size_t sz = regerror( err, &cmd_reg, NULL, 0 );
+    char buf[sz];
+    regerror( err, &cmd_reg, buf, sz );
+    syslog( LOG_CRIT, "Internal error: third regex, %s", buf );
+    fprintf( stderr, "Internal error compiling third regular expression: %s\n", buf );
+    return 1;
+  };
+
+  if ( ! regexec( &cmd_reg, argv[2], 0, NULL, 0 ) ) {
+    syslog( LOG_ERR, "Invalid command '%s' (third regex)", argv[2] );
+    fprintf( stderr, "'%s' does not appear to be a valid command!\n", argv[2] );
+    return 1;
+  };
+
+  regfree( &cmd_reg );
+
+  struct passwd *pwd = getpwnam( argv[1] );
+
+  if ( ! pwd ) {
+    syslog( LOG_ERR, "Invalid username '%s' (getpwnam)", argv[1] );
+    fprintf( stderr, "'%s' does not appear to be a valid username!\n", argv[1] );
+    return 1;
+  };
+
+  if ( pwd->pw_uid < 1000 ) {
+    syslog( LOG_ERR, "Invalid username '%s' (uid)", argv[1] );
+    fprintf( stderr, "'%s' does not appear to be a valid username!\n", argv[1] );
+    return 1;
+  };
+
+  if ( setregid( pwd->pw_gid, pwd->pw_gid ) != 0 ) {
+    err = errno;
+    syslog( LOG_ERR, "Unable to change GID: %s, %s", argv[2], strerror( err ) );
+    fprintf( stderr, "Unable to change GID: %s\n", strerror( err ) );
+    return 1;
+  };
+
+  if ( setreuid( pwd->pw_uid, pwd->pw_uid ) != 0 ) {
+    err = errno;
+    syslog( LOG_ERR, "Unable to change UID: %s, %s", argv[2], strerror( err ) );
+    fprintf( stderr, "Unable to change UID: %s\n", strerror( err ) );
+    return 1;
+  };
+
+  size_t sz = snprintf( NULL, 0, "/usr/share/piny-suid/%s", argv[2] );
+  char buf[sz];
+  snprintf( buf, sz, "/usr/share/piny-suid/%s", argv[2] );
+
+  char * const env[] =
+    { NULL
+    };
+
+  syslog( LOG_NOTICE, "Going to exec '%s' as '%s'", argv[2], argv[1] );
+  execve( buf, argv + 2, env );
+
+  syslog( LOG_ERR, "Invalid command '%s' (fell past exec)", argv[2] );
+  fprintf( stderr, "'%s' does not appear to be a valid command!\n", argv[2] );
+  return 1;
+
+};