libselinux: verify file_contexts when using restorecon

In permissive mode, calling restorecon with a bad label in file_contexts does not verify the label's existence in the loaded policy. This results in any label successfully applying to a file, as long as the file exists.

This issue has two assumptions:
1) file_contexts must be manually updated with the invalid label. Running semanage fcontext will error when attempting to add an invalid label to file_contexts.
2) the system must be in permissive. Although applying an invalid label in enforcing gives an error and fails, successfully labeling a file with a bad label could cause issues during policy development in permissive.

Instead of the current behavior, mimic setfiles' -c flag, and verify the labels against the loaded policy binary.

Behavior before patch:

$ sudo -s
$ setenforce 0
$ echo '/test.txt       --      system_u:object_r:foo_bar_baz:s0' >> /etc/selinux/targeted/contexts/files/file_contexts
$ restorecon -v /test.txt
Relabeled /test.txt from system_u:object_r:etc_runtime_t:s0 to system_u:object_r:foo_bar_baz:s0

Behavior after patch:

$ sudo -s
$ setenforce 0
$ echo '/test.txt       --      system_u:object_r:foo_bar_baz:s0' >> /etc/selinux/targeted/contexts/files/file_contexts
$ restorecon -v /test.txt
restorecon: /etc/selinux/targeted/contexts/files/file_contexts: line 6123 has invalid context system_u:object_r:foo_bar_baz:s0
Invalid argument

Signed-off-by Yuli Khodorkovskiy <[email protected]>

---
 policycoreutils/setfiles/setfiles.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

policycoreutils/setfiles/setfiles.c +0 -0

index bc83c27b..ce1e4324 100644

policycoreutils/setfiles/setfiles.c +1 -1

 		 */
 		if (strcmp(base, RESTORECON))
 			fprintf(stderr, "Executed with unrecognized name (%s), defaulting to %s behavior.\n",

@@ -230,7 +230,7 @@ int main(int argc, char **argv)
 		r_opts.add_assoc = 0;
 		r_opts.xdev = 0;
 		r_opts.ignore_mounts = 0;
-		ctx_validate = 0;
+		ctx_validate = 1;
 		opts = ropts;
 
 		/* restorecon only:  silent exit if no SELinux.

Quoted 11 lines · Yuli Khodorkovskiy

In permissive mode, calling restorecon with a bad label in file_contexts does not verify the label's existence in the loaded policy. This results in any label successfully applying to a file, as long as the file exists.

This issue has two assumptions:
1) file_contexts must be manually updated with the invalid label. Running semanage fcontext will error when attempting to add an invalid label to file_contexts.
2) the system must be in permissive. Although applying an invalid label in enforcing gives an error and fails, successfully labeling a file with

a

Quoted 3 lines

bad label could cause issues during policy development in permissive.

Instead of the current behavior, mimic setfiles' -c flag, and verify the

labels

Quoted 7 lines

against the loaded policy binary.

Behavior before patch:

$ sudo -s
$ setenforce 0
$ echo '/test.txt       --      system_u:object_r:foo_bar_baz:s0' >>

/etc/selinux/targeted/contexts/files/file_contexts

Quoted 2 lines

$ restorecon -v /test.txt
Relabeled /test.txt from system_u:object_r:etc_runtime_t:s0 to

system_u:object_r:foo_bar_baz:s0

Quoted 6 lines

Behavior after patch:

$ sudo -s
$ setenforce 0
$ echo '/test.txt       --      system_u:object_r:foo_bar_baz:s0' >>

/etc/selinux/targeted/contexts/files/file_contexts

Quoted 2 lines

$ restorecon -v /test.txt
restorecon: /etc/selinux/targeted/contexts/files/file_contexts: line

6123 has invalid context system_u:object_r:foo_bar_baz:s0

Review

Quoted 8 lines

Invalid argument

Signed-off-by Yuli Khodorkovskiy <[email protected]>

---
 policycoreutils/setfiles/setfiles.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

(quoted diff) +0 -0

b/policycoreutils/setfiles/setfiles.c

policycoreutils/setfiles/setfiles.c int main(int argc, char **argv) · line 218

Quoted 6 lines

index bc83c27b..ce1e4324 100644

policycoreutils/setfiles/setfiles.c +0 -0

@@ -217,7 +217,7 @@ int main(int argc, char **argv)
               * Do not abort on errors during the file tree walk,
               * Do not try to track inode associations for conflict

detection,

policycoreutils/setfiles/setfiles.c int main(int argc, char **argv) · line 220

Quoted 3 lines

policycoreutils/setfiles/setfiles.c +1 -1

               * Follows mounts,
-              * Does lazy validation of contexts upon use.
+              * Validates all file contexts at init time.

I think this was intentional; the reason they didn't want to validate all file contexts at init time for restorecon was that they didn't want a single error in file_contexts to prevent restorecon from working at all (e.g. one typo could kill restorecon -R /dev during boot, even if the erroneous entry had nothing to do with /dev). Instead, I think we were doing validation lazily for the context to be used, e.g. matchpathcon() or selabel_lookup() would validate the context before returning it. Looking at the code, we do call compat_validate() in selabel_fini(), which occurs just prior to returning a result from lookup. And this will call selabel_validate() unless the caller has set an invalidcon or canoncon callback (legacy matchpathcon support). And selabel_validate() has a check to see if the individual context has already been validated (contexts->validated), but it also presently returns immediately if the caller did not set validation up front. Meanwhile, process_line() and load_mmap() don't even call selabel_validate() if !rec->validating. I think it is a bug in selabel_validate() that it is returning immediately if !rec->validating. During initialization (i.e. loading of file_contexts or

file_contexts.bin by process_line() or load_mmap() respectively), we should only call selabel_validate() if rec->validating (as is presently done). But at lookup, selabel_fini() should call selabel_validate() and that should validate the context unless it has already been validated (based on contexts->validated), irrespective of rec->validating. That's the lazy validation part. Then we get validation before any context gets used but we don't break entirely if there is a single bad entry in file_contexts. Sound reasonable?

policycoreutils/setfiles/setfiles.c int main(int argc, char **argv)

Quoted 4 lines

policycoreutils/setfiles/setfiles.c +0 -0

               */
              if (strcmp(base, RESTORECON))
                      fprintf(stderr, "Executed with unrecognized name

(%s), defaulting to %s behavior.\n",

Quoted 10 lines

policycoreutils/setfiles/setfiles.c +1 -1

@@ -230,7 +230,7 @@ int main(int argc, char **argv)
              r_opts.add_assoc = 0;
              r_opts.xdev = 0;
              r_opts.ignore_mounts = 0;
-             ctx_validate = 0;
+             ctx_validate = 1;
              opts = ropts;
 
              /* restorecon only:  silent exit if no SELinux.