1 #include <stdio.h> |
1 #include <stdio.h> |
2 #include <stdlib.h> |
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3 #include <unistd.h> |
2 #include <unistd.h> |
4 #include <errno.h> |
3 #include <errno.h> |
5 |
4 |
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5 FILE *f; //file pointer |
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6 |
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7 //tests return errno = 13 for permission denied |
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8 void read_test(char *name) |
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9 { |
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10 if ((f = fopen(name, "r")) == NULL) { |
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11 printf("%s is not readable, errno = %d\n", name, errno); |
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12 } else { |
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13 printf("%s is readable\n", name); fclose(f); |
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14 } |
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15 } |
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16 |
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17 void write_test(char *name) |
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18 { |
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19 if ((f = fopen(name, "r+")) == NULL) { |
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20 printf("%s is not writable, errno = %d\n", name, errno); |
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21 } else { |
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22 printf("%s is writable\n", name); fclose(f); |
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23 } |
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24 } |
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25 |
6 int main(int argc, char *argv[]) |
26 int main(int argc, char *argv[]) |
7 { |
27 { |
8 FILE *f; //file pointer |
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9 |
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10 printf("Real UID = %d\n", getuid()); |
28 printf("Real UID = %d\n", getuid()); |
11 printf("Effective UID = %d\n", geteuid()); |
29 printf("Effective UID = %d\n", geteuid()); |
12 |
30 |
13 //read test (error 13 is permission denied) |
31 read_test(argv[1]); |
14 if ((f = fopen(argv[1], "r")) == NULL) { |
32 write_test(argv[1]); |
15 fprintf(stderr, "%s is not readable, errno = %d\n", argv[1], errno); |
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16 } else { |
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17 fprintf(stderr, "%s is readable\n", argv[1]); fclose(f); |
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18 } |
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19 |
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20 //write test |
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21 if ((f = fopen(argv[1], "r+")) == NULL) { |
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22 fprintf(stderr, "%s is not writable, errno = %d\n", argv[1], errno); |
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23 } else { |
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24 fprintf(stderr, "%s is writable\n", argv[1]); fclose(f); |
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25 } |
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26 |
33 |
27 //lowering the access rights to the caller |
34 //lowering the access rights to the caller |
28 if (setuid(getuid())) { |
35 if (setuid(getuid())) { |
29 fprintf(stderr, "could not reset setuid, errno = %d\n", errno); return 1; |
36 printf("could not reset setuid, errno = %d\n", errno); |
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37 return 1; |
30 } |
38 } |
31 |
39 |
32 printf("Real UID = %d\n", getuid()); |
40 printf("Real UID = %d\n", getuid()); |
33 printf("Effective UID = %d\n", geteuid()); |
41 printf("Effective UID = %d\n", geteuid()); |
34 |
42 |
35 //read test |
43 read_test(argv[1]); |
36 if ((f = fopen(argv[1], "r")) == NULL) { |
44 write_test(argv[1]); |
37 fprintf(stderr, "%s is not readable, errno = %d\n", argv[1], errno); |
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38 } else { |
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39 fprintf(stderr, "%s is readable\n", argv[1]); fclose(f); |
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40 } |
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41 |
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42 //write test |
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43 if ((f = fopen(argv[1], "w")) == NULL) { |
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44 fprintf(stderr, "%s is not writable, errno = %d\n", argv[1], errno); |
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45 } else { |
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46 fprintf(stderr, "%s is writable\n", argv[1]); fclose(f); |
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47 } |
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48 |
45 |
49 return 0; |
46 return 0; |
50 } |
47 } |