Implement sudo_intercept.so.

Uses protobuf to talk to main sudo process over a socketpair.

src/sudo_intercept.c

@@ -0,0 +1,126 @@
+/*
+ * SPDX-License-Identifier: ISC
+ *
+ * Copyright (c) 2021 Todd C. Miller <Todd.Miller@sudo.ws>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/*
+ * This is an open source non-commercial project. Dear PVS-Studio, please check it.
+ * PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
+ */
+
+#include <config.h>
+
+#include <sys/types.h>
+
+#include <errno.h>
+#include <stdarg.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#ifdef HAVE_STDBOOL_H
+# include <stdbool.h>
+#else
+# include "compat/stdbool.h"
+#endif /* HAVE_STDBOOL_H */
+#if defined(HAVE_SHL_LOAD)
+# include <dl.h>
+#elif defined(HAVE_DLOPEN)
+# include <dlfcn.h>
+#endif
+
+#include "sudo_compat.h"
+#include "pathnames.h"
+
+extern bool command_allowed(const char *cmnd, char * const argv[], char * const envp[], char **ncmnd, char ***nargv, char ***nenvp);
+
+#ifdef HAVE___INTERPOSE
+/*
+ * Mac OS X 10.4 and above has support for library symbol interposition.
+ * There is a good explanation of this in the Mac OS X Internals book.
+ */
+typedef struct interpose_s {
+    void *new_func;
+    void *orig_func;
+} interpose_t;
+
+static int
+my_execve(const char *cmnd, char * const argv[], char * const envp[])
+{
+    char *ncmnd = NULL, **nargv = NULL, **nenvp = NULL;
+
+    /* XXX - add SUDO_INTERCEPT_FD to environment as needed. */
+    if (command_allowed(cmnd, argv, envp, &ncmnd, &nargv, &nenvp)) {
+	/* Execute the command using the "real" execve() function. */
+	execve(ncmnd, nargv, nenvp);
+    } else {
+	errno = EACCES;
+    }
+    /* XXX - free ncmnd, nargv, nenvp */
+    return -1;
+}
+
+/* Magic to tell dyld to do symbol interposition. */
+__attribute__((__used__)) static const interpose_t interposers[]
+__attribute__((__section__("__DATA,__interpose"))) = {
+    { (void *)my_execve, (void *)execve }
+};
+
+#else /* HAVE___INTERPOSE */
+
+typedef int (*sudo_fn_execve_t)(const char *, char *const *, char *const *);
+
+sudo_dso_public int
+execve(const char *cmnd, char * const argv[], char * const envp[])
+{
+    char *ncmnd = NULL, **nargv = NULL, **nenvp = NULL;
+# if defined(HAVE_DLOPEN)
+    void *fn = dlsym(RTLD_NEXT, "execve");
+# elif defined(HAVE_SHL_LOAD)
+    const char *name, *myname = _PATH_SUDO_INTERCEPT;
+    struct shl_descriptor *desc;
+    void *fn = NULL;
+    int idx = 0;
+
+    /* Search for execve() but skip this shared object. */
+    myname = sudo_basename(myname);
+    while (shl_get(idx++, &desc) == 0) {
+        name = sudo_basename(desc->filename);
+        if (strcmp(name, myname) == 0)
+            continue;
+        if (shl_findsym(&desc->handle, "execve", TYPE_PROCEDURE, &fn) == 0)
+            break;
+    }
+# else
+    void *fn = NULL;
+# endif
+    if (fn == NULL) {
+        errno = EACCES;
+        return -1;
+    }
+
+    /* XXX - add SUDO_INTERCEPT_FD to environment as needed. */
+    if (command_allowed(cmnd, argv, envp, &ncmnd, &nargv, &nenvp)) {
+	/* Execute the command using the "real" execve() function. */
+	return ((sudo_fn_execve_t)fn)(ncmnd, nargv, nenvp);
+    } else {
+	errno = EACCES;
+    }
+    /* XXX - free ncmnd, nargv, nenvp */
+    return -1;
+}
+#endif /* HAVE___INTERPOSE) */