Re: [PATCH v3 3/3] LSM: Add context interface for proc attr
From: Casey Schaufler
Date: Tue Jun 14 2016 - 16:19:57 EST
On 6/14/2016 11:57 AM, Kees Cook wrote:
> On Fri, Jun 10, 2016 at 2:25 PM, Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote:
>> Subject: [PATCH v3 3/3] LSM: Add context interface for proc attrs
>>
>> The /proc/.../attr/current interface is used by all three
>> Linux security modules (SELinux, Smack and AppArmor) to
>> report and modify the process security attribute. This is
>> all fine when there is exactly one of these modules active
>> and the userspace code knows which it module it is.
>> It would require a major change to the "current" interface
>> to provide information about more than one set of process
>> security attributes. Instead, a "context" attribute is
>> added, which identifies the security module that the
>> information applies to. The format is:
>>
>> lsmname='context-value'
>>
>> When multiple concurrent modules are supported the
>> /proc/.../attr/context interface will include the data
>> for all of the active modules.
>>
>> lsmname1='context-value1'lsmname2='context-value2'
> For humans to read this, could we add a space between each?
You can't use it in audit records or SO_PEERSEC if you
put whitespace in it.
>> The module specific subdirectories under attr contain context
>> entries that report the information for that specific module
>> in the same format.
>>
>> Signed-off-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
>>
>> ---
>> fs/proc/base.c | 4 ++
>> security/apparmor/lsm.c | 34 ++++++++++++++--
>> security/security.c | 97 ++++++++++++++++++++++++++++++++++++++++++++++
>> security/selinux/hooks.c | 22 ++++++++++-
>> security/smack/smack_lsm.c | 21 ++++++----
>> 5 files changed, 164 insertions(+), 14 deletions(-)
>>
>> diff --git a/fs/proc/base.c b/fs/proc/base.c
>> index 182bc28..df94f26 100644
>> --- a/fs/proc/base.c
>> +++ b/fs/proc/base.c
>> @@ -2532,6 +2532,7 @@ static const struct pid_entry selinux_attr_dir_stuff[] = {
>> ATTR("selinux", "fscreate", S_IRUGO|S_IWUGO),
>> ATTR("selinux", "keycreate", S_IRUGO|S_IWUGO),
>> ATTR("selinux", "sockcreate", S_IRUGO|S_IWUGO),
>> + ATTR("selinux", "context", S_IRUGO|S_IWUGO),
>> };
>> LSM_DIR_OPS(selinux);
>> #endif
>> @@ -2539,6 +2540,7 @@ LSM_DIR_OPS(selinux);
>> #ifdef CONFIG_SECURITY_SMACK
>> static const struct pid_entry smack_attr_dir_stuff[] = {
>> ATTR("smack", "current", S_IRUGO|S_IWUGO),
>> + ATTR("smack", "context", S_IRUGO|S_IWUGO),
>> };
>> LSM_DIR_OPS(smack);
>> #endif
>> @@ -2548,6 +2550,7 @@ static const struct pid_entry apparmor_attr_dir_stuff[] = {
>> ATTR("apparmor", "current", S_IRUGO|S_IWUGO),
>> ATTR("apparmor", "prev", S_IRUGO),
>> ATTR("apparmor", "exec", S_IRUGO|S_IWUGO),
>> + ATTR("apparmor", "context", S_IRUGO|S_IWUGO),
>> };
>> LSM_DIR_OPS(apparmor);
>> #endif
>> @@ -2559,6 +2562,7 @@ static const struct pid_entry attr_dir_stuff[] = {
>> ATTR(NULL, "fscreate", S_IRUGO|S_IWUGO),
>> ATTR(NULL, "keycreate", S_IRUGO|S_IWUGO),
>> ATTR(NULL, "sockcreate", S_IRUGO|S_IWUGO),
>> + ATTR(NULL, "context", S_IRUGO|S_IWUGO),
>> #ifdef CONFIG_SECURITY_SELINUX
>> DIR("selinux", S_IRUGO|S_IXUGO,
>> proc_selinux_attr_dir_inode_ops, proc_selinux_attr_dir_ops),
>> diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
>> index fb0fb03..3790a7d 100644
>> --- a/security/apparmor/lsm.c
>> +++ b/security/apparmor/lsm.c
>> @@ -479,6 +479,8 @@ static int apparmor_getprocattr(struct task_struct *task, char *name,
>>
>> if (strcmp(name, "current") == 0)
>> profile = aa_get_newest_profile(cxt->profile);
>> + else if (strcmp(name, "context") == 0)
>> + profile = aa_get_newest_profile(cxt->profile);
>> else if (strcmp(name, "prev") == 0 && cxt->previous)
>> profile = aa_get_newest_profile(cxt->previous);
>> else if (strcmp(name, "exec") == 0 && cxt->onexec)
>> @@ -486,8 +488,29 @@ static int apparmor_getprocattr(struct task_struct *task, char *name,
>> else
>> error = -EINVAL;
>>
>> - if (profile)
>> - error = aa_getprocattr(profile, value);
>> + if (profile) {
>> + if (strcmp(name, "context") == 0) {
>> + char *vp;
>> + char *np;
>> +
>> + error = aa_getprocattr(profile, &vp);
>> + if (error > 0) {
>> + error += 12;
>> + *value = kzalloc(error, GFP_KERNEL);
>> + if (*value == NULL)
>> + error = -ENOMEM;
>> + else {
>> + sprintf(*value, "apparmor='%s'", vp);
>> + np = strchr(*value, '\n');
>> + if (np != NULL) {
>> + np[0] = '\'';
>> + np[1] = '\0';
>> + }
>> + }
>> + }
>> + } else
>> + error = aa_getprocattr(profile, value);
>> + }
>>
>> aa_put_profile(profile);
>> put_cred(cred);
>> @@ -530,7 +553,7 @@ static int apparmor_setprocattr(struct task_struct *task, char *name,
>> return -EINVAL;
>>
>> arg_size = size - (args - (char *) value);
>> - if (strcmp(name, "current") == 0) {
>> + if (strcmp(name, "current") == 0 || strcmp(name, "context") == 0) {
>> if (strcmp(command, "changehat") == 0) {
>> error = aa_setprocattr_changehat(args, arg_size,
>> !AA_DO_TEST);
>> @@ -552,7 +575,10 @@ static int apparmor_setprocattr(struct task_struct *task, char *name,
>> else
>> goto fail;
>> } else
>> - /* only support the "current" and "exec" process attributes */
>> + /*
>> + * only support the "current", context and "exec"
>> + * process attributes
>> + */
>> return -EINVAL;
>>
>> if (!error)
>> diff --git a/security/security.c b/security/security.c
>> index 41ac80d..6f7ad19 100644
>> --- a/security/security.c
>> +++ b/security/security.c
>> @@ -1187,8 +1187,49 @@ int security_getprocattr(struct task_struct *p, const char *lsm, char *name,
>> char **value)
>> {
>> struct security_hook_list *hp;
>> + char *vp;
>> + char *cp = NULL;
>> int rc = -EINVAL;
>> + int trc;
>>
>> + /*
>> + * "context" requires work here in addition to what
>> + * the modules provide.
>> + */
>> + if (strcmp(name, "context") == 0) {
>> + *value = NULL;
>> + list_for_each_entry(hp,
>> + &security_hook_heads.getprocattr, list) {
>> + if (lsm != NULL && strcmp(lsm, hp->lsm))
>> + continue;
>> + trc = hp->hook.getprocattr(p, "context", &vp);
>> + if (trc == -ENOENT)
>> + continue;
>> + if (trc <= 0) {
>> + kfree(*value);
>> + return trc;
>> + }
>> + rc = trc;
>> + if (*value == NULL) {
>> + *value = vp;
>> + } else {
>> + cp = kzalloc(strlen(*value) + strlen(vp) + 1,
>> + GFP_KERNEL);
>> + if (cp == NULL) {
>> + kfree(*value);
>> + kfree(vp);
>> + return -ENOMEM;
>> + }
>> + sprintf(cp, "%s%s", *value, vp);
> This is another place kasprinf() would be cleaner.
Agreed. Will make the change.
>
>> + kfree(*value);
>> + kfree(vp);
>> + *value = cp;
>> + }
>> + }
>> + if (rc > 0)
>> + return strlen(*value);
>> + return rc;
>> + }
>>
>> list_for_each_entry(hp, &security_hook_heads.getprocattr, list) {
>> if (lsm != NULL && strcmp(lsm, hp->lsm))
>> @@ -1205,7 +1246,63 @@ int security_setprocattr(struct task_struct *p, const char *lsm, char *name,
>> {
>> struct security_hook_list *hp;
>> int rc = -EINVAL;
>> + char *local;
>> + char *cp;
>> + int slen;
>> + int failed = 0;
>>
>> + /*
>> + * "context" is handled directly here.
>> + */
>> + if (strcmp(name, "context") == 0) {
>> + /*
>> + * First verify that the input is acceptable.
>> + * lsm1='v1'lsm2='v2'lsm3='v3'
>> + *
>> + * A note on the use of strncmp() below.
>> + * The check is for the substring at the beginning of cp.
>> + */
> I'd add a note that this is creating a NULL-terminated string. Though
> to that end, should NULL bytes be invalid in the input string? It
> could confuse things.
>
>> + local = kzalloc(size + 1, GFP_KERNEL);
>> + memcpy(local, value, size);
>> + cp = local;
>> + list_for_each_entry(hp, &security_hook_heads.setprocattr,
>> + list) {
>> + if (lsm != NULL && strcmp(lsm, hp->lsm))
>> + continue;
>> + slen = strlen(hp->lsm);
>> + if (strncmp(cp, hp->lsm, slen))
>> + goto free_out;
>> + cp += slen;
>> + if (cp[0] != '=' || cp[1] != '\'' || cp[2] == '\'')
>> + goto free_out;
>> + for (cp += 2; cp[0] != '\''; cp++)
>> + if (cp[0] == '\0')
>> + goto free_out;
>> + cp++;
>> + }
> Is it okay that this loop allows unknown LSMs to be input? (I think
It requires that all the necessary data be supplied, and in the
correct order. Once it has it, it stops. There could be a check that
there isn't anything beyond the last entry. I'm not worried about
that.
> it's okay.) Also, should lsm == NULL be checked early and
> rejected/skipped so the lsm != NULL test isn't needed in both loops?
Ah, you miss the nuance of the code. NULL is an acceptance condition,
not a rejection as it would be in most cases.
>> + cp = local;
>> + list_for_each_entry(hp, &security_hook_heads.setprocattr,
>> + list) {
>> + if (lsm != NULL && strcmp(lsm, hp->lsm))
>> + continue;
>> + cp += strlen(hp->lsm) + 2;
>> + for (slen = 0; cp[slen] != '\''; slen++)
>> + ;
>> + cp[slen] = '\0';
>> +
>> + rc = hp->hook.setprocattr(p, "context", cp, slen);
>> + if (rc < 0)
>> + failed = rc;
>> + cp += slen + 1;
>> + }
>> + if (failed != 0)
>> + rc = failed;
>> + else
>> + rc = size;
>> +free_out:
>> + kfree(local);
>> + return rc;
>> + }
>> list_for_each_entry(hp, &security_hook_heads.setprocattr, list) {
>> if (lsm != NULL && strcmp(lsm, hp->lsm))
>> continue;
>> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
>> index ed3a757..3a21c2b 100644
>> --- a/security/selinux/hooks.c
>> +++ b/security/selinux/hooks.c
>> @@ -5711,6 +5711,8 @@ static int selinux_getprocattr(struct task_struct *p,
>>
>> if (!strcmp(name, "current"))
>> sid = __tsec->sid;
>> + else if (!strcmp(name, "context"))
>> + sid = __tsec->sid;
>> else if (!strcmp(name, "prev"))
>> sid = __tsec->osid;
>> else if (!strcmp(name, "exec"))
>> @@ -5728,7 +5730,21 @@ static int selinux_getprocattr(struct task_struct *p,
>> if (!sid)
>> return 0;
>>
>> - error = security_sid_to_context(sid, value, &len);
>> + if (strcmp(name, "context")) {
>> + error = security_sid_to_context(sid, value, &len);
>> + } else {
>> + char *vp;
>> +
>> + error = security_sid_to_context(sid, &vp, &len);
>> + if (!error) {
>> + *value = kzalloc(len + 10, GFP_KERNEL);
>> + if (*value == NULL)
>> + error = -ENOMEM;
>> + else
>> + sprintf(*value, "selinux='%s'", vp);
> More kasprintf...
Indeed.
>
>> + }
>> + }
>> +
>> if (error)
>> return error;
>> return len;
>> @@ -5768,6 +5784,8 @@ static int selinux_setprocattr(struct task_struct *p,
>> error = current_has_perm(p, PROCESS__SETSOCKCREATE);
>> else if (!strcmp(name, "current"))
>> error = current_has_perm(p, PROCESS__SETCURRENT);
>> + else if (!strcmp(name, "context"))
>> + error = current_has_perm(p, PROCESS__SETCURRENT);
>> else
>> error = -EINVAL;
>> if (error)
>> @@ -5827,7 +5845,7 @@ static int selinux_setprocattr(struct task_struct *p,
>> tsec->keycreate_sid = sid;
>> } else if (!strcmp(name, "sockcreate")) {
>> tsec->sockcreate_sid = sid;
>> - } else if (!strcmp(name, "current")) {
>> + } else if (!strcmp(name, "current") || !strcmp(name, "context")) {
>> error = -EINVAL;
>> if (sid == 0)
>> goto abort_change;
>> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
>> index 3577009..d2d8624 100644
>> --- a/security/smack/smack_lsm.c
>> +++ b/security/smack/smack_lsm.c
>> @@ -3576,16 +3576,21 @@ static int smack_getprocattr(struct task_struct *p, char *name, char **value)
>> char *cp;
>> int slen;
>>
>> - if (strcmp(name, "current") != 0)
>> + if (strcmp(name, "current") == 0) {
>> + cp = kstrdup(skp->smk_known, GFP_KERNEL);
>> + if (cp == NULL)
>> + return -ENOMEM;
>> + } else if (strcmp(name, "context") == 0) {
>> + slen = strlen(skp->smk_known) + 9;
>> + cp = kzalloc(slen, GFP_KERNEL);
>> + if (cp == NULL)
>> + return -ENOMEM;
>> + sprintf(cp, "smack='%s'", skp->smk_known);
> And more kasprintf
Yes.
>> + } else
>> return -EINVAL;
>>
>> - cp = kstrdup(skp->smk_known, GFP_KERNEL);
>> - if (cp == NULL)
>> - return -ENOMEM;
>> -
>> - slen = strlen(cp);
>> *value = cp;
>> - return slen;
>> + return strlen(cp);
>> }
>>
>> /**
>> @@ -3622,7 +3627,7 @@ static int smack_setprocattr(struct task_struct *p, char *name,
>> if (value == NULL || size == 0 || size >= SMK_LONGLABEL)
>> return -EINVAL;
>>
>> - if (strcmp(name, "current") != 0)
>> + if (strcmp(name, "current") != 0 && strcmp(name, "context") != 0)
>> return -EINVAL;
>>
>> skp = smk_import_entry(value, size);
>>
> Otherwise, looks good to me.
>
> -Kees
>