restorecon context validation improvement

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, as each context is used, verify it is valid before blindly applying the label. If an error with validation occurs in restorecon, application of remaining valid labels will be uninterrupted as before.

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

---
 libselinux/src/label.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

libselinux/src/label.c +0 -0

index 48f4d2d6..e642a97b 100644

Quoted 35 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 bad label could cause issues during policy development in permissive.

Instead, as each context is used, verify it is valid before blindly applying the label. If an error with validation occurs in restorecon, application of remaining valid labels will be uninterrupted as before.

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

---
 libselinux/src/label.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

libselinux/src/label.c +1 -1

index 48f4d2d6..e642a97b 100644
@@ -126,7 +126,7 @@ int selabel_validate(struct selabel_handle *rec,
 {
      int rc = 0;
 
-     if (!rec->validating || contexts->validated)
+     if (contexts->validated)
              goto out;
 

libselinux/src/label.c int selabel_validate(struct selabel_handle *rec, · line 132

Quoted 2 lines

libselinux/src/label.c +0 -0

      rc = selinux_validate(&contexts->ctx_raw);

label.c: In function ‘selabel_validate’:
label.c:124:45: error: unused parameter ‘rec’ [-Werror=unused-parameter]
int selabel_validate(struct selabel_handle *rec,

                                             ^~~

Need to drop the rec argument to selabel_validate() since it is no longer used.

Keep track of line numbers for each file context in selabel_handle. If an error occurs in selabel_fini(), the line number of an invalid file context is echoed to the user.

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

---
 libselinux/src/label.c          | 2 +-
 libselinux/src/label_file.h     | 1 +
 libselinux/src/label_internal.h | 1 +
 3 files changed, 3 insertions(+), 1 deletion(-)

libselinux/src/label.c +1 -1

index e642a97b..d9a58ce9 100644
@@ -143,7 +143,7 @@ static int selabel_fini(struct selabel_handle *rec,
 			    struct selabel_lookup_rec *lr,
 			    int translating)
 {
-	if (compat_validate(rec, lr, rec->spec_file, 0))
+	if (compat_validate(rec, lr, rec->spec_file, lr->lineno))
 		return -1;
 
 	if (translating && !lr->ctx_trans &&

libselinux/src/label_file.h +1 -0

index aa576d8e..4780ae48 100644
@@ -472,6 +472,7 @@ static inline int process_line(struct selabel_handle *rec,
 	spec_arr[nspec].mode = 0;
 
 	spec_arr[nspec].lr.ctx_raw = context;
+	spec_arr[nspec].lr.lineno = lineno;
 
 	/*
 	 * bump data->nspecs to cause closef() to cover it in its free

libselinux/src/label_internal.h +0 -0

index c55efb75..0e020557 100644

libselinux/src/label_file.h static inline int process_line(struct selabel_handle

Quoted 29 lines · Yuli Khodorkovskiy

Keep track of line numbers for each file context in selabel_handle. If an error occurs in selabel_fini(), the line number of an invalid file context is echoed to the user.

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

---
 libselinux/src/label.c          | 2 +-
 libselinux/src/label_file.h     | 1 +
 libselinux/src/label_internal.h | 1 +
 3 files changed, 3 insertions(+), 1 deletion(-)

libselinux/src/label.c +1 -1

index e642a97b..d9a58ce9 100644
@@ -143,7 +143,7 @@ static int selabel_fini(struct selabel_handle *rec,
                          struct selabel_lookup_rec *lr,
                          int translating)
 {
-     if (compat_validate(rec, lr, rec->spec_file, 0))
+     if (compat_validate(rec, lr, rec->spec_file, lr->lineno))
              return -1;
 
      if (translating && !lr->ctx_trans &&

libselinux/src/label_file.h +0 -0

index aa576d8e..4780ae48 100644
@@ -472,6 +472,7 @@ static inline int process_line(struct selabel_handle

*rec,

libselinux/src/label_

Quoted 8 lines

libselinux/src/label_file.h +1 -0

      spec_arr[nspec].mode = 0;
 
      spec_arr[nspec].lr.ctx_raw = context;
+     spec_arr[nspec].lr.lineno = lineno;
 
      /*
       * bump data->nspecs to cause closef() to cover it in its free

libselinux/src/label_ renamed from libselinux/src/label_internal.h +0 -0

internal.h

Quoted 10 lines

index c55efb75..0e020557 100644

libselinux/src/label_internal.h +1 -0

@@ -73,6 +73,7 @@ struct selabel_lookup_rec {
      char * ctx_raw;
      char * ctx_trans;
      int validated;
+     unsigned lineno;
 };
 

libselinux/src/label_internal.h struct selabel_lookup_rec { · line 79

Quoted 2 lines

libselinux/src/label_internal.h +0 -0

 struct selabel_handle {

I think this is ok, but wanted to double check: does this work correctly when file contexts are loaded from
file_contexts.bin instead? It looks to me as if the lineno will be left as 0 in that case and the
code will handle that correctly.

The other question is whether we correctly report the file name when the entry comes from a file other
than file_contexts itself, e.g. file_contexts.local, .homedirs, ... Not your bug if we don't but wondered.

On Thu, Mar 29, 2018 at 9:49 AM, Stephen Smalley <[email protected] <mailto:[email protected]>> wrote:

    On 03/28/2018 11:40 PM, Yuli Khodorkovskiy wrote:
    > Keep track of line numbers for each file context in
    > selabel_handle. If an error occurs in selabel_fini(), the
    > line number of an invalid file context is echoed to the user.
    >
    > Signed-off-by: Yuli Khodorkovskiy <[email protected] <mailto:[email protected]>>
    > ---
    >  libselinux/src/label.c          | 2 +-
    >  libselinux/src/label_file.h     | 1 +
    >  libselinux/src/label_internal.h | 1 +
    >  3 files changed, 3 insertions(+), 1 deletion(-)
    >
    > diff --git a/libselinux/src/label.c b/libselinux/src/label.c
    > index e642a97b..d9a58ce9 100644
    > --- a/libselinux/src/label.c
    > +++ b/libselinux/src/label.c
    > @@ -143,7 +143,7 @@ static int selabel_fini(struct selabel_handle *rec,
    >                           struct selabel_lookup_rec *lr,
    >                           int translating)
    >  {
    > -     if (compat_validate(rec, lr, rec->spec_file, 0))
    > +     if (compat_validate(rec, lr, rec->spec_file, lr->lineno))
    >               return -1;
    >
    >       if (translating && !lr->ctx_trans &&
    > diff --git a/libselinux/src/label_file.h b/libselinux/src/label_file.h
    > index aa576d8e..4780ae48 100644
    > --- a/libselinux/src/label_file.h
    > +++ b/libselinux/src/label_file.h
    > @@ -472,6 +472,7 @@ static inline int process_line(struct selabel_handle *rec,
    >       spec_arr[nspec].mode = 0;
    >
    >       spec_arr[nspec].lr.ctx_raw = context;
    > +     spec_arr[nspec].lr.lineno = lineno;
    >
    >       /*
    >        * bump data->nspecs to cause closef() to cover it in its free
    > diff --git a/libselinux/src/label_internal.h b/libselinux/src/label_internal.h
    > index c55efb75..0e020557 100644
    > --- a/libselinux/src/label_internal.h
    > +++ b/libselinux/src/label_internal.h
    > @@ -73,6 +73,7 @@ struct selabel_lookup_rec {
    >       char * ctx_raw;
    >       char * ctx_trans;
    >       int validated;
    > +     unsigned lineno;
    >  };
    >
    >  struct selabel_handle {
    >

    I think this is ok, but wanted to double check: does this work correctly when file contexts are loaded from
    file_contexts.bin instead?  It looks to me as if the lineno will be left as 0 in that case and the
    code will handle that correctly.

Compiling a file_contexts.bin with sefcontext_compile will give you the line number:

sefcontext_compile /etc/selinux/targeted/contexts/files/file_contexts -o file_contexts.bin -p /etc/selinux/targeted/policy/policy.31 libsepol.sepol_context_from_string: malformed context "test"
libsepol.sepol_context_from_string: could not construct context from string
libsepol.context_from_string: could not create context structure
libsepol.sepol_context_to_sid: could not convert test to sid /etc/selinux/targeted/contexts/files/file_contexts: line 6132 has invalid context test
sefcontext_compile: process_file failed

Using file_contexts.bin for relabeling that I generated with no validation will not report a line number:

restorecon: /etc/selinux/targeted/contexts/files/file_contexts: has invalid context test

I'll see if I can associate the line number with each regex in sefcontext_compile.

The other question is whether we correctly report the file name when the entry comes from a file other than file_contexts itself, e.g. file_contexts.local, .homedirs, ...  Not your bug if we don't but wondered.

It is reporting the line number correctly, but the filename is incorrect. I'll update this.

Quoted 70 lines · Yuli Khodorkovskiy

On Thu, Mar 29, 2018 at 9:49 AM, Stephen Smalley <[email protected] <mailto:[email protected]>> wrote:

    On 03/28/2018 11:40 PM, Yuli Khodorkovskiy wrote:
    > Keep track of line numbers for each file context in
    > selabel_handle. If an error occurs in selabel_fini(), the
    > line number of an invalid file context is echoed to the user.
    >
    > Signed-off-by: Yuli Khodorkovskiy <[email protected] <mailto:[email protected]>>
    > ---
    >  libselinux/src/label.c          | 2 +-
    >  libselinux/src/label_file.h     | 1 +
    >  libselinux/src/label_internal.h | 1 +
    >  3 files changed, 3 insertions(+), 1 deletion(-)
    >
    > diff --git a/libselinux/src/label.c b/libselinux/src/label.c
    > index e642a97b..d9a58ce9 100644
    > --- a/libselinux/src/label.c
    > +++ b/libselinux/src/label.c
    > @@ -143,7 +143,7 @@ static int selabel_fini(struct selabel_handle *rec,
    >                           struct selabel_lookup_rec *lr,
    >                           int translating)
    >  {
    > -     if (compat_validate(rec, lr, rec->spec_file, 0))
    > +     if (compat_validate(rec, lr, rec->spec_file, lr->lineno))
    >               return -1;
    >
    >       if (translating && !lr->ctx_trans &&
    > diff --git a/libselinux/src/label_file.h b/libselinux/src/label_file.h
    > index aa576d8e..4780ae48 100644
    > --- a/libselinux/src/label_file.h
    > +++ b/libselinux/src/label_file.h
    > @@ -472,6 +472,7 @@ static inline int process_line(struct selabel_handle *rec,
    >       spec_arr[nspec].mode = 0;
    >
    >       spec_arr[nspec].lr.ctx_raw = context;
    > +     spec_arr[nspec].lr.lineno = lineno;
    >
    >       /*
    >        * bump data->nspecs to cause closef() to cover it in its free
    > diff --git a/libselinux/src/label_internal.h b/libselinux/src/label_internal.h
    > index c55efb75..0e020557 100644
    > --- a/libselinux/src/label_internal.h
    > +++ b/libselinux/src/label_internal.h
    > @@ -73,6 +73,7 @@ struct selabel_lookup_rec {
    >       char * ctx_raw;
    >       char * ctx_trans;
    >       int validated;
    > +     unsigned lineno;
    >  };
    >
    >  struct selabel_handle {
    >

    I think this is ok, but wanted to double check: does this work correctly when file contexts are loaded from
    file_contexts.bin instead?  It looks to me as if the lineno will be left as 0 in that case and the
    code will handle that correctly.

Compiling a file_contexts.bin with sefcontext_compile will give you the line number:

sefcontext_compile /etc/selinux/targeted/contexts/files/file_contexts -o file_contexts.bin -p /etc/selinux/targeted/policy/policy.31 libsepol.sepol_context_from_string: malformed context "test"
libsepol.sepol_context_from_string: could not construct context from string
libsepol.context_from_string: could not create context structure
libsepol.sepol_context_to_sid: could not convert test to sid /etc/selinux/targeted/contexts/files/file_contexts: line 6132 has invalid context test
sefcontext_compile: process_file failed

Quoted 5 lines

Using file_contexts.bin for relabeling that I generated with no validation will not report a line number:

restorecon: /etc/selinux/targeted/contexts/files/file_contexts: has invalid context test

I'll see if I can associate the line number with each regex in sefcontext_compile.

That's fine if you want to do it but not necessary for these patches to be merged; I just wanted to ensure that we don't have garbage output as a result of these patches. I'd do it as a separate patch regardless since it likely requires a new binary format version for the file_contexts.bin files.

Quoted 5 lines

The other question is whether we correctly report the file name when the entry comes from a file other than file_contexts itself, e.g. file_contexts.local, .homedirs, ... Not your bug if we don't but wondered.

It is reporting the line number correctly, but the filename is incorrect. I'll update this.

Again, not strictly necessary for these patches since you didn't introduce the bug, and probably ought to be its own separate patch.

In permissive, if a bad label is written to a file_context file, restorecon will not verify the label before succesfully applying the context. These patches fix validation of labels during restorecon while not breaking current behavior of lazy validation.

Yuli Khodorkovskiy (2):
libselinux: verify file_contexts when using restorecon
libselinux: echo line number of bad label in selabel_fini()

 libselinux/src/label.c          | 4 ++--
 libselinux/src/label_file.h     | 1 +
 libselinux/src/label_internal.h | 1 +
 3 files changed, 4 insertions(+), 2 deletions(-)

--
2.14.3