Re: semodule/libsemanage patch to allow enable and disable of modules.

[Joshua Brindle <method@manicmethod.com>]

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Chad Sellers wrote:
> On 8/28/09 1:58 PM, "Daniel J Walsh"<dwalsh@redhat.com>  wrote:
>
>    
>> The general idea is to relabel a disabled policy module as
>> policymodule.pp.disabled
>>
>> Then make sure -u and -i update this name.
>>
>> Rebuilding policy does not include .disabled
>>
>> Listing shows disabled as disabled.
>>
>> semodule -r will remove disabled modules. If you reinstall they will come
>> back.
>>
>> # /usr/sbin/semodule -d unconfined
>> # /usr/sbin/semodule -l | grep unc
>> unconfined 3.0.1 Disabled
>> unconfineduser 1.0.0
>> # ls -lZ /etc/selinux/targeted/modules/active/modules/unconfined.pp*
>> -rw-------. root root staff_u:object_r:semanage_store_t:s0
>> /etc/selinux/targeted/modules/active/modules/unconfined.pp.disabled
>> # /usr/sbin/semodule -i /usr/share/selinux/targeted/unconfined.pp.bz2
>> # /usr/sbin/semodule -l | grep unc
>> unconfined 3.0.1 Disabled
>> unconfineduser 1.0.0
>> # /usr/sbin/semodule -e unconfined
>> # /usr/sbin/semodule -l | grep unc
>> unconfined 3.0.1
>> unconfineduser 1.0.0
>>
>> This would allow an admin to disable a module and the module will stay
>> disabled until he enables it.
>>      
> <snip>
>    
>> diff --git a/libsemanage/src/direct_api.c b/libsemanage/src/direct_api.c
>> index f7d65eb..49a2357 100644
>> --- a/libsemanage/src/direct_api.c
>> +++ b/libsemanage/src/direct_api.c
>> @@ -53,6 +53,8 @@
>>   #include "policy.h"
>>   #include<sys/mman.h>
>>
>> +static const char *DISABLESTR=".disabled";
>> +
>>   static void semanage_direct_destroy(semanage_handle_t * sh);
>>   static int semanage_direct_disconnect(semanage_handle_t * sh);
>>   static int semanage_direct_begintrans(semanage_handle_t * sh);
>> @@ -66,6 +68,8 @@ static int semanage_direct_upgrade_file(semanage_handle_t *
>> sh, const char *modu
>>   static int semanage_direct_install_base(semanage_handle_t * sh, char
>> *base_data,
>>                       size_t data_len);
>>   static int semanage_direct_install_base_file(semanage_handle_t * sh, const
>> char *module_name);
>> +static int semanage_direct_enable(semanage_handle_t * sh, char *module_name);
>> +static int semanage_direct_disable(semanage_handle_t * sh, char
>> *module_name);
>>   static int semanage_direct_remove(semanage_handle_t * sh, char *module_name);
>>   static int semanage_direct_list(semanage_handle_t * sh,
>>                   semanage_module_info_t ** modinfo,
>> @@ -83,6 +87,8 @@ static struct semanage_policy_table direct_funcs = {
>>       .upgrade_file = semanage_direct_upgrade_file,
>>       .install_base = semanage_direct_install_base,
>>       .install_base_file = semanage_direct_install_base_file,
>> +    .enable = semanage_direct_enable,
>> +    .disable = semanage_direct_disable,
>>       .remove = semanage_direct_remove,
>>       .list = semanage_direct_list
>>   };
>> @@ -1002,6 +1008,17 @@ static int semanage_direct_commit(semanage_handle_t *
>> sh)
>>       return retval;
>>   }
>>
>> +static char * get_store_name(const char *file)
>> +{
>> +    int len = strlen(file) + strlen(DISABLESTR) + 1;
>> +    char *storename = calloc(1, len);
>> +    if (! storename) return NULL;
>> +    snprintf(storename,len, "%s%s", file, DISABLESTR);
>> +    if ( access(storename, F_OK) == 0) return storename;
>> +    free(storename);
>> +    return strdup(file);
>> +}
>> +
>>   /* Writes a module to the sandbox's module directory, overwriting any
>>    * previous module stored within.  Note that module data are not
>>    * free()d by this function; caller is responsible for deallocating it
>> @@ -1019,11 +1036,20 @@ static int semanage_direct_install(semanage_handle_t *
>> sh,
>>                          &filename)) != 0) {
>>           goto cleanup;
>>       }
>> -    if (bzip(sh, filename, data, data_len)<= 0) {
>> +
>> +    char *storename = get_store_name(filename);
>> +    if (!storename) {
>> +        ERR(sh, "Could not allocate memory");
>> +        retval = -1;
>> +        goto cleanup;
>> +    }
>> +    if (bzip(sh, storename, data, data_len)<= 0) {
>>      
>
> Should we present some sort of warning to the user if they install/upgrade a
> module that is disabled? This seems to maintain the disabled status
> silently, which might confuse users (e.g. "I just installed that module, why
> isn't the policy working").
>
> Also, I see that you patched direct_install, but not direct_upgrade. So,
> upgrade will try to re-enable the module if it has been disabled.
>
>    
>>           ERR(sh, "Error while writing to %s.", filename);
>>           retval = -3;
>>           goto cleanup;
>>       }
>> +    free(storename);
>> +
>>       retval = 0;
>>         cleanup:
>>       free(version);
>> @@ -1268,6 +1294,107 @@ static int
>> semanage_direct_install_base_file(semanage_handle_t * sh,
>>       return retval;
>>   }
>>
>> +/* Enables a module from the sandbox.  Returns 0 on success, -1 if out
>> + * of memory, -2 if module not found or could not be enabled. */
>> +static int semanage_direct_enable(semanage_handle_t * sh, char *module_name)
>> +{
>> +    int i, retval = -1;
>> +    char **module_filenames = NULL;
>> +    int num_mod_files;
>> +    size_t name_len = strlen(module_name);
>> +    if (semanage_get_modules_names(sh,&module_filenames,&num_mod_files) ==
>> +        -1) {
>> +        return -1;
>> +    }
>> +    for (i = 0; i<  num_mod_files; i++) {
>> +        char *base = strrchr(module_filenames[i], '/');
>> +        if (base == NULL) {
>> +            ERR(sh, "Could not read module names.");
>> +            retval = -2;
>> +            goto cleanup;
>> +        }
>> +        base++;
>> +        if (memcmp(module_name, base, name_len) == 0&&
>> +            strcmp(base + name_len + 3, DISABLESTR) == 0) {
>> +            int len = strlen(module_filenames[i]) - strlen(DISABLESTR);
>> +            char *enabled_name = calloc(1, len+1);
>> +            if (!enabled_name) {
>> +                ERR(sh, "Could not allocate memory");
>> +                retval = -1;
>> +                goto cleanup;
>> +            }
>> +
>> +            strncpy(enabled_name, module_filenames[i],len);
>> +
>> +            if (rename(module_filenames[i], enabled_name) == -1) {
>> +                ERR(sh, "Could not enable module file %s.",
>> +                    enabled_name);
>> +                retval = -2;
>> +            }
>> +            retval = 0;
>> +            free(enabled_name);
>> +            goto cleanup;
>> +        }
>> +    }
>> +    ERR(sh, "Module %s was not found.", module_name);
>> +    retval = -2;        /* module not found */
>> +      cleanup:
>> +    for (i = 0; module_filenames != NULL&&  i<  num_mod_files; i++) {
>> +        free(module_filenames[i]);
>> +    }
>> +    free(module_filenames);
>> +    return retval;
>> +}
>> +
>> +/* Enables a module from the sandbox.  Returns 0 on success, -1 if out
>> + * of memory, -2 if module not found or could not be enabled. */
>> +static int semanage_direct_disable(semanage_handle_t * sh, char *module_name)
>> +{
>> +    int i, retval = -1;
>> +    char **module_filenames = NULL;
>> +    int num_mod_files;
>> +    size_t name_len = strlen(module_name);
>> +    if (semanage_get_modules_names(sh,&module_filenames,&num_mod_files) ==
>> +        -1) {
>> +        return -1;
>> +    }
>> +    for (i = 0; i<  num_mod_files; i++) {
>> +        char *base = strrchr(module_filenames[i], '/');
>> +        if (base == NULL) {
>> +            ERR(sh, "Could not read module names.");
>> +            retval = -2;
>> +            goto cleanup;
>> +        }
>> +        base++;
>> +        if (memcmp(module_name, base, name_len) == 0&&
>> +            strcmp(base + name_len, ".pp") == 0) {
>> +            char disabled_name[PATH_MAX];
>> +            if (snprintf(disabled_name, PATH_MAX, "%s%s",
>> +                     module_filenames[i], DISABLESTR) == PATH_MAX) {
>> +                ERR(sh, "Could not disable module file %s.",
>> +                    module_filenames[i]);
>> +                retval = -2;
>> +                goto cleanup;
>> +            }
>> +            if (rename(module_filenames[i], disabled_name) == -1) {
>> +                ERR(sh, "Could not disable module file %s.",
>> +                    module_filenames[i]);
>> +                retval = -2;
>> +            }
>> +            retval = 0;
>> +            goto cleanup;
>> +        }
>> +    }
>> +    ERR(sh, "Module %s was not found.", module_name);
>> +    retval = -2;        /* module not found */
>> +      cleanup:
>> +    for (i = 0; module_filenames != NULL&&  i<  num_mod_files; i++) {
>> +        free(module_filenames[i]);
>> +    }
>> +    free(module_filenames);
>> +    return retval;
>> +}
>> +
>>      
> While this function does succeed in renaming a file, it does not succeed in
> preventing the module from being linked in. semanage_get_modules_names()
> grabs everything in the modules directory, so the disabled modules here are
> still linked into the policy. A quick sesearch confirms this.
>
> To fix this, you'll either need to modify semanage_filename_select() to
> filter out files ending in .disabled or perhaps just move them from the
> modules directory to a disabled_modules directory (instead of the rename).
> The latter option has the advantage of not requiring filtering that could go
> wrong at some point, so I would lean toward it.
>
> Thanks,
> Chad
>
>
>    


Do you have an updated version of this?

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