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77 lines
2 KiB
C
77 lines
2 KiB
C
#include <stdlib.h>
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#include <stdio.h>
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#include <string.h>
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#include <unistd.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <dirent.h>
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#include <assert.h>
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/* Make sure assertions are not compiled out. */
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#undef NDEBUG
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extern char **environ;
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static char * wrapperDir = WRAPPER_DIR;
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int main(int argc, char * * argv)
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{
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char self[PATH_MAX];
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int len = readlink("/proc/self/exe", self, sizeof(self) - 1);
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assert (len > 0);
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self[len] = 0;
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/* Make sure that we are being executed from the right location,
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i.e., `wrapperDir'. This is to prevent someone from
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creating hard link `X' from some other location, along with a
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false `X.real' file, to allow arbitrary programs from being
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executed setuid. */
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assert ((strncmp(self, wrapperDir, sizeof(wrapperDir)) == 0) &&
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(self[strlen(wrapperDir)] == '/'));
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/* Make *really* *really* sure that we were executed as `self',
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and not, say, as some other setuid program. That is, our
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effective uid/gid should match the uid/gid of `self'. */
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//printf("%d %d\n", geteuid(), getegid());
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struct stat st;
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assert (lstat(self, &st) != -1);
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//printf("%d %d\n", st.st_uid, st.st_gid);
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assert ((st.st_mode & S_ISUID) == 0 ||
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(st.st_uid == geteuid()));
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assert ((st.st_mode & S_ISGID) == 0 ||
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st.st_gid == getegid());
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/* And, of course, we shouldn't be writable. */
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assert (!(st.st_mode & (S_IWGRP | S_IWOTH)));
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/* Read the path of the real (wrapped) program from <self>.real. */
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char realFN[PATH_MAX + 10];
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int realFNSize = snprintf (realFN, sizeof(realFN), "%s.real", self);
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assert (realFNSize < sizeof(realFN));
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int fdSelf = open(realFN, O_RDONLY);
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assert (fdSelf != -1);
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char real[PATH_MAX];
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len = read(fdSelf, real, PATH_MAX);
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assert (len != -1);
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assert (len < sizeof (real));
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assert (len > 0);
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real[len] = 0;
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close(fdSelf);
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//printf("real = %s, len = %d\n", real, len);
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execve(real, argv, environ);
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exit(1);
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}
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