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su: Make it setuid root, ask for a password, and accept a username

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It asks for a password only if you are not root, obviously.
This commit is contained in:
apio 2022-10-28 20:57:13 +02:00
parent 477af66cdc
commit 5aba1c5f15
2 changed files with 45 additions and 5 deletions
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1
apps/Makefile
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@ -17,6 +17,7 @@ build: $(REAL_APPS)
install: $(REAL_APPS)
@mkdir -p $(LUNA_ROOT)/initrd/bin
cp $(REAL_APPS) $(LUNA_ROOT)/initrd/bin
@chmod a+s $(LUNA_ROOT)/initrd/bin/su
clean:
rm -f $(APPS_BIN)/*

49
apps/src/su.c
View File

@ -1,9 +1,10 @@
#include <errno.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
char* default_argv[] = {"/bin/sh", NULL};
void run_program(char** argv)
{
execv(argv[0], argv);
@ -12,26 +13,64 @@ void run_program(char** argv)
exit(EXIT_FAILURE);
}
void strip_newline(char* str)
{
size_t len = strlen(str);
if (str[len - 1] == '\n') str[len - 1] = 0;
}
int main(int argc, char** argv)
{
if (argc == 1)
{
fprintf(stderr, "Usage: %s [uid] [command | sh]\n", argv[0]);
fprintf(stderr, "Usage: %s [username] [command | login shell]\n", argv[0]);
return EXIT_FAILURE;
}
if (setuid(atoi(argv[1])) < 0)
if (getuid() != 0)
{
fprintf(stderr, "%s must be setuid root", argv[0]);
return EXIT_FAILURE;
}
struct passwd* user = getpwnam(argv[1]);
if (!user)
{
if (errno) perror("getpwnam");
else
fprintf(stderr, "Unknown user %s\n", argv[1]);
return EXIT_FAILURE;
}
if (getuid() != geteuid()) // we were started from a non-root user
{
printf("Password: ");
char buf[BUFSIZ];
fgets(buf, BUFSIZ, stdin);
strip_newline(buf);
putchar('\n');
if (strcmp(buf, user->pw_passwd) != 0)
{
fprintf(stderr, "Invalid password\n");
return EXIT_FAILURE;
}
}
if (setuid(user->pw_uid) < 0)
{
perror("setuid");
return EXIT_FAILURE;
}
if (setgid(atoi(argv[1])) < 0)
if (setgid(user->pw_gid) < 0)
{
perror("setgid");
return EXIT_FAILURE;
}
char* default_argv[] = {user->pw_shell, NULL};
if (argc == 2) run_program(default_argv);
else
run_program(argv + 2);