unistd: Interpose execv* functions for LOADER

Newer releases of Chromium directly execv /proc/self/exe, missing our
readlink(3) interposing.  We go ahead and interpose all three execv*
functions just to ensure wider compatibility.

2 files changed, 60 insertions, 1 deletions

diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index a4d7698..1330b68 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -8,9 +8,14 @@
   © 2016-2019 Adélie Linux and contributors.  NCSA open source licence.
 
 
-1.0.0 (20??-??-??)
+0.9.0 (2020-07-??)
 ==================
 
+unistd
+------
+
+* Add execv/execve/execvp family of functions to catch exec of /proc/self/exe.
+
 wchar
 -----
 
diff --git a/libgcompat/unistd.c b/libgcompat/unistd.c
index d2f3097..d632eee 100644
--- a/libgcompat/unistd.c
+++ b/libgcompat/unistd.c
@@ -3,6 +3,10 @@
 #include <limits.h> /* NGROUPS_MAX */
 #include <stddef.h> /* NULL, size_t */
 #include <unistd.h> /* confstr, getcwd, getgroups, ... */
+#include <errno.h>  /* ENOSYS, ENOMEM */
+#include <stdlib.h> /* calloc */
+#include <dlfcn.h>  /* dlsym */
+#include <string.h> /* strcmp */
 
 #include "alias.h" /* alias */
 
@@ -179,3 +183,53 @@ int group_member(gid_t gid)
 
 	return 0;
 }
+
+#ifndef LOADER
+#error LOADER must be defined
+#endif
+
+static int (*real_execve)(const char *pathname, char *const argv[], char *const envp[]);
+int execve(const char *pathname, char *const argv[], char *const envp[]) {
+	if(real_execve == NULL) {
+		real_execve = dlsym(RTLD_NEXT, "execve");
+		if(real_execve == NULL) {
+			errno = ENOSYS;
+			return -1;
+		}
+	}
+
+	if(!strcmp(pathname, "/proc/self/exe")) {
+		char **new_argv;
+		char target[PATH_MAX] = "";
+		int argc = 0, i = 0;
+		while(argv[i++] != 0) argc++;
+
+		i = readlink("/proc/self/exe", target, sizeof(target));
+		if(i < 0 || i == sizeof(target)) {
+			errno = ENOMEM;
+			return -1;
+		}
+
+		new_argv = calloc(argc + 6, sizeof(char *));
+		new_argv[0] = LOADER;
+		new_argv[1] = "--argv0";
+		new_argv[2] = argv[0];
+		new_argv[3] = "--preload";
+		new_argv[4] = "/lib/libgcompat.so.0";
+		new_argv[5] = target;
+		for(int j = 1, i = 6; j < argc; ++i, ++j) {
+			new_argv[i] = argv[j];
+		}
+		return execve(LINKER, new_argv, envp);
+	}
+	return real_execve(pathname, argv, envp);
+}
+
+extern char **environ;
+int execv(const char *pathname, char *const argv[]) {
+	return execve(pathname, argv, environ);
+}
+
+int execvp(const char *file, char *const argv[]) {
+	return execv(file, argv);
+}