[lxc-devel] Question: Some confusion about lxc-test-apparmor #2206

[Hongzhi, Song]

I have some confusion about source code of lxc-test-apparmor defined in 
'lxc/src/tests/aa.c'.

  * The output of||
  * |lxc-test-apparmor|

|passed with /sys/kernel/uevent_helper passed with /proc/sys/fs/file-nr 
failed - opened /sys/kernel/mm/ksm/pages_to_scan |

  * |ls -l /sys/kernel/uevent_helper|
  * |ls -l /sys/kernel/mm/ksm/pages_to_scan|

|root at intel-x86-64:# ls -l /sys/kernel/uevent_helper ls: cannot access 
'/sys/kernel/uevent_helper': No such file or directory 
root at intel-x86-64:# ls -l /sys/kernel/mm/ksm/pages_to_scan -rw-r--r-- 1 
root root 4096 Mar 6 19:17 /sys/kernel/mm/ksm/pages_to_scan |


        Issue description

As shown above, /sys/kernel/mm/ksm/pages_to_scan is exist, and can be 
opened. But error message prompts that fail to open it.
I refer to source code lxc/src/tests/aa.c, branch master.

|108 char *files_to_deny[] = { 109 "/sys/kernel/uevent_helper", 110 
"/proc/sys/fs/file-nr", 111 "/sys/kernel/mm/ksm/pages_to_scan", 112 
"/proc/sys/kernel/sysrq", 113 NULL }; |

|115 static bool test_aa_policy(struct lxc_container *c) 116 { 117 int i, 
ret; 118 119 for (i = 0; files_to_deny[i]; i++) { 120 ret = 
do_test_file_open(c, files_to_deny[i]); 121 if (ret < 0) { 122 
fprintf(stderr, "attach failed; skipping test\n"); 123 return true; 124 
} 125 if (ret > 0) { 126 fprintf(stderr, "failed - opened %s\n", 127 
files_to_deny[i]); 128 return false; 129 } 130 fprintf(stderr, "passed 
with %s\n", files_to_deny[i]); 131 } ...... |

|63 static int do_test_file_open(struct lxc_container *c, char *fnam) 64 
{ 65 int fret = -1; 66 int ret; 67 pid_t pid; 68 int pipefd[2]; 69 char 
result[1024]; 70 lxc_attach_options_t attach_options = 
LXC_ATTACH_OPTIONS_DEFAULT; 71 72 ret = pipe(pipefd); 73 if (ret < 0) { 
74 fprintf(stderr, "pipe failed %d\n", ret); 75 return fret; 76 } 77 
attach_options.stdout_fd = pipefd[1]; 78 attach_options.attach_flags &= 
~(LXC_ATTACH_LSM_EXEC|LXC_ATTACH_DROP_CAPABILITIES); 79 
attach_options.attach_flags |= LXC_ATTACH_LSM_NOW; 80 ret = c->attach(c, 
test_attach_write_file, fnam, &attach_options, &pid); ...... 85 86 ret = 
read(pipefd[0], result, sizeof(result)-1); 87 if (ret < 0) { 88 
fprintf(stderr, "read failed %d\n", ret); 89 goto err2; 90 } 91 92 fret 
= 1; 93 if (strncmp(result, "no", 2) == 0) 94 fret = 0; ...... 101 
return fret; 102 } |

|41 static int test_attach_write_file(void* payload) 42 { 43 char *fnam = 
payload; 44 FILE *f; 45 46 f = fopen(fnam, "w"); 47 if (f) { 48 
printf("yes\n"); 49 fclose(f); 50 fflush(NULL); 51 return 1; 52 } 53 
printf("no\n"); 54 fflush(NULL); 55 return 0; 56 } |

Line46-48: If open interfaces successfully listed in files_to_deny[], 
Line108, printf 'yes' into pipe[1].
Line86: And then pipe[0] reads out 'yes'.
Line92-101: If result is 'yes', do_test_file_open() will return 1.
Line125-128: If the return of do_test_file_open() is 1, then fprintf( 
failed open).
So can anyone tell me why files listed in files_to_deny[] exit but print 
fail.

Thanks.


||

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