@ -2,12 +2,12 @@
# include <stdio.h> # include <stdio.h>
# include <string.h> # include <string.h>
# include <unistd.h> # include <unistd.h>
# include <stdnoreturn.h>
# include <sys/types.h> # include <sys/types.h>
# include <sys/stat.h> # include <sys/stat.h>
# include <sys/xattr.h> # include <sys/xattr.h>
# include <fcntl.h> # include <fcntl.h>
# include <dirent.h> # include <dirent.h>
# include <assert.h>
# include <errno.h> # include <errno.h>
# include <linux/capability.h> # include <linux/capability.h>
# include <sys/prctl.h> # include <sys/prctl.h>
@ -16,10 +16,7 @@
# include <syscall.h> # include <syscall.h>
# include <byteswap.h> # include <byteswap.h>
// Make sure assertions are not compiled out, we use them to codify
# define ASSERT(expr) ((expr) ? (void) 0 : assert_failure(#expr))
// invariants about this program and we want it to fail fast and
// loudly if they are violated.
# undef NDEBUG
extern char * * environ ; extern char * * environ ;
@ -38,6 +35,12 @@ static char *wrapper_debug = "WRAPPER_DEBUG";
# define LE32_TO_H(x) (x) # define LE32_TO_H(x) (x)
# endif # endif
static noreturn void assert_failure ( const char * assertion ) {
fprintf ( stderr , " Assertion `%s` in NixOS's wrapper.c failed. \n " , assertion ) ;
fflush ( stderr ) ;
abort ( ) ;
}
int get_last_cap ( unsigned * last_cap ) { int get_last_cap ( unsigned * last_cap ) {
FILE * file = fopen ( " /proc/sys/kernel/cap_last_cap " , " r " ) ; FILE * file = fopen ( " /proc/sys/kernel/cap_last_cap " , " r " ) ;
if ( file = = NULL ) { if ( file = = NULL ) {
@ -167,6 +170,7 @@ int readlink_malloc(const char *p, char **ret) {
} }
int main ( int argc , char * * argv ) { int main ( int argc , char * * argv ) {
ASSERT ( argc > = 1 ) ;
char * self_path = NULL ; char * self_path = NULL ;
int self_path_size = readlink_malloc ( " /proc/self/exe " , & self_path ) ; int self_path_size = readlink_malloc ( " /proc/self/exe " , & self_path ) ;
if ( self_path_size < 0 ) { if ( self_path_size < 0 ) {
@ -181,36 +185,36 @@ int main(int argc, char **argv) {
int len = strlen ( wrapper_dir ) ; int len = strlen ( wrapper_dir ) ;
if ( len > 0 & & ' / ' = = wrapper_dir [ len - 1 ] ) if ( len > 0 & & ' / ' = = wrapper_dir [ len - 1 ] )
- - len ; - - len ;
assert ( ! strncmp ( self_path , wrapper_dir , len ) ) ; ASSERT ( ! strncmp ( self_path , wrapper_dir , len ) ) ;
assert ( ' / ' = = wrapper_dir [ 0 ] ) ; ASSERT ( ' / ' = = wrapper_dir [ 0 ] ) ;
assert ( ' / ' = = self_path [ len ] ) ; ASSERT ( ' / ' = = self_path [ len ] ) ;
// Make *really* *really* sure that we were executed as
// Make *really* *really* sure that we were executed as
// `self_path', and not, say, as some other setuid program. That
// `self_path', and not, say, as some other setuid program. That
// is, our effective uid/gid should match the uid/gid of
// is, our effective uid/gid should match the uid/gid of
// `self_path'.
// `self_path'.
struct stat st ; struct stat st ;
assert ( lstat ( self_path , & st ) ! = - 1 ) ; ASSERT ( lstat ( self_path , & st ) ! = - 1 ) ;
assert ( ! ( st . st_mode & S_ISUID ) | | ( st . st_uid = = geteuid ( ) ) ) ; ASSERT ( ! ( st . st_mode & S_ISUID ) | | ( st . st_uid = = geteuid ( ) ) ) ;
assert ( ! ( st . st_mode & S_ISGID ) | | ( st . st_gid = = getegid ( ) ) ) ; ASSERT ( ! ( st . st_mode & S_ISGID ) | | ( st . st_gid = = getegid ( ) ) ) ;
// And, of course, we shouldn't be writable.
// And, of course, we shouldn't be writable.
assert ( ! ( st . st_mode & ( S_IWGRP | S_IWOTH ) ) ) ; ASSERT ( ! ( st . st_mode & ( S_IWGRP | S_IWOTH ) ) ) ;
// Read the path of the real (wrapped) program from <self>.real.
// Read the path of the real (wrapped) program from <self>.real.
char real_fn [ PATH_MAX + 10 ] ; char real_fn [ PATH_MAX + 10 ] ;
int real_fn_size = snprintf ( real_fn , sizeof ( real_fn ) , " %s.real " , self_path ) ; int real_fn_size = snprintf ( real_fn , sizeof ( real_fn ) , " %s.real " , self_path ) ;
assert ( real_fn_size < sizeof ( real_fn ) ) ; ASSERT ( real_fn_size < sizeof ( real_fn ) ) ;
int fd_self = open ( real_fn , O_RDONLY ) ; int fd_self = open ( real_fn , O_RDONLY ) ;
assert ( fd_self ! = - 1 ) ; ASSERT ( fd_self ! = - 1 ) ;
char source_prog [ PATH_MAX ] ; char source_prog [ PATH_MAX ] ;
len = read ( fd_self , source_prog , PATH_MAX ) ; len = read ( fd_self , source_prog , PATH_MAX ) ;
assert ( len ! = - 1 ) ; ASSERT ( len ! = - 1 ) ;
assert ( len < sizeof ( source_prog ) ) ; ASSERT ( len < sizeof ( source_prog ) ) ;
assert ( len > 0 ) ; ASSERT ( len > 0 ) ;
source_prog [ len ] = 0 ; source_prog [ len ] = 0 ;
close ( fd_self ) ; close ( fd_self ) ;
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