[PATCH v17 22/23] LSM: Add /proc attr entry for full LSM context
Casey Schaufler
casey at schaufler-ca.com
Thu May 14 22:11:41 UTC 2020
Add an entry /proc/.../attr/context which displays the full
process security "context" in compound format:
lsm1\0value\0lsm2\0value\0...
This entry is not writable.
Reviewed-by: Kees Cook <keescook at chromium.org>
Signed-off-by: Casey Schaufler <casey at schaufler-ca.com>
Cc: linux-api at vger.kernel.org
---
Documentation/security/lsm.rst | 28 +++++++++++++
fs/proc/base.c | 1 +
include/linux/lsm_hooks.h | 6 +++
security/apparmor/include/procattr.h | 2 +-
security/apparmor/lsm.c | 8 +++-
security/apparmor/procattr.c | 22 +++++-----
security/security.c | 63 ++++++++++++++++++++++++++++
security/selinux/hooks.c | 2 +-
security/smack/smack_lsm.c | 2 +-
9 files changed, 119 insertions(+), 15 deletions(-)
diff --git a/Documentation/security/lsm.rst b/Documentation/security/lsm.rst
index aadf47c808c0..304260778cab 100644
--- a/Documentation/security/lsm.rst
+++ b/Documentation/security/lsm.rst
@@ -199,3 +199,31 @@ capability-related fields:
- ``fs/nfsd/auth.c``::c:func:`nfsd_setuser()`
- ``fs/proc/array.c``::c:func:`task_cap()`
+
+LSM External Interfaces
+=======================
+
+The LSM infrastructure does not generally provide external interfaces.
+The individual security modules provide what external interfaces they
+require.
+
+The file ``/sys/kernel/security/lsm`` provides a comma
+separated list of the active security modules.
+
+The file ``/proc/pid/attr/display`` contains the name of the security
+module for which the ``/proc/pid/attr/current`` interface will
+apply. This interface can be written to.
+
+The infrastructure does provide an interface for the special
+case where multiple security modules provide a process context.
+This is provided in compound context format.
+
+- `lsm\0value\0lsm\0value\0`
+
+The `lsm` and `value` fields are nul terminated bytestrings.
+Each field may contain whitespace or non-printable characters.
+The nul bytes are included in the size of a compound context.
+The context ``Bell\0Secret\0Biba\0Loose\0`` has a size of 23.
+
+The file ``/proc/pid/attr/context`` provides the security
+context of the identified process.
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 8217e2642096..3983b29316ea 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2778,6 +2778,7 @@ static const struct pid_entry attr_dir_stuff[] = {
ATTR(NULL, "keycreate", 0666),
ATTR(NULL, "sockcreate", 0666),
ATTR(NULL, "display", 0666),
+ ATTR(NULL, "context", 0444),
#ifdef CONFIG_SECURITY_SMACK
DIR("smack", 0555,
proc_smack_attr_dir_inode_ops, proc_smack_attr_dir_ops),
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 7799c6d2a63a..c986cd21cb4f 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1342,6 +1342,12 @@
* @pages contains the number of pages.
* Return 0 if permission is granted.
*
+ * @getprocattr:
+ * Provide the named process attribute for display in special files in
+ * the /proc/.../attr directory. Attribute naming and the data displayed
+ * is at the discretion of the security modules. The exception is the
+ * "context" attribute, which will contain the security context of the
+ * task as a nul terminated text string without trailing whitespace.
* @ismaclabel:
* Check if the extended attribute specified by @name
* represents a MAC label. Returns 1 if name is a MAC
diff --git a/security/apparmor/include/procattr.h b/security/apparmor/include/procattr.h
index 31689437e0e1..03dbfdb2f2c0 100644
--- a/security/apparmor/include/procattr.h
+++ b/security/apparmor/include/procattr.h
@@ -11,7 +11,7 @@
#ifndef __AA_PROCATTR_H
#define __AA_PROCATTR_H
-int aa_getprocattr(struct aa_label *label, char **string);
+int aa_getprocattr(struct aa_label *label, char **string, bool newline);
int aa_setprocattr_changehat(char *args, size_t size, int flags);
#endif /* __AA_PROCATTR_H */
diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index 16b992235c11..02f305ab2c69 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -593,6 +593,7 @@ static int apparmor_getprocattr(struct task_struct *task, char *name,
const struct cred *cred = get_task_cred(task);
struct aa_task_ctx *ctx = task_ctx(current);
struct aa_label *label = NULL;
+ bool newline = true;
if (strcmp(name, "current") == 0)
label = aa_get_newest_label(cred_label(cred));
@@ -600,11 +601,14 @@ static int apparmor_getprocattr(struct task_struct *task, char *name,
label = aa_get_newest_label(ctx->previous);
else if (strcmp(name, "exec") == 0 && ctx->onexec)
label = aa_get_newest_label(ctx->onexec);
- else
+ else if (strcmp(name, "context") == 0) {
+ label = aa_get_newest_label(cred_label(cred));
+ newline = false;
+ } else
error = -EINVAL;
if (label)
- error = aa_getprocattr(label, value);
+ error = aa_getprocattr(label, value, newline);
aa_put_label(label);
put_cred(cred);
diff --git a/security/apparmor/procattr.c b/security/apparmor/procattr.c
index c929bf4a3df1..be3b083d9b74 100644
--- a/security/apparmor/procattr.c
+++ b/security/apparmor/procattr.c
@@ -20,6 +20,7 @@
* aa_getprocattr - Return the profile information for @profile
* @profile: the profile to print profile info about (NOT NULL)
* @string: Returns - string containing the profile info (NOT NULL)
+ * @newline: Should a newline be added to @string.
*
* Returns: length of @string on success else error on failure
*
@@ -30,20 +31,21 @@
*
* Returns: size of string placed in @string else error code on failure
*/
-int aa_getprocattr(struct aa_label *label, char **string)
+int aa_getprocattr(struct aa_label *label, char **string, bool newline)
{
struct aa_ns *ns = labels_ns(label);
struct aa_ns *current_ns = aa_get_current_ns();
+ int flags = FLAG_VIEW_SUBNS | FLAG_HIDDEN_UNCONFINED;
int len;
if (!aa_ns_visible(current_ns, ns, true)) {
aa_put_ns(current_ns);
return -EACCES;
}
+ if (newline)
+ flags |= FLAG_SHOW_MODE;
- len = aa_label_snxprint(NULL, 0, current_ns, label,
- FLAG_SHOW_MODE | FLAG_VIEW_SUBNS |
- FLAG_HIDDEN_UNCONFINED);
+ len = aa_label_snxprint(NULL, 0, current_ns, label, flags);
AA_BUG(len < 0);
*string = kmalloc(len + 2, GFP_KERNEL);
@@ -52,19 +54,19 @@ int aa_getprocattr(struct aa_label *label, char **string)
return -ENOMEM;
}
- len = aa_label_snxprint(*string, len + 2, current_ns, label,
- FLAG_SHOW_MODE | FLAG_VIEW_SUBNS |
- FLAG_HIDDEN_UNCONFINED);
+ len = aa_label_snxprint(*string, len + 2, current_ns, label, flags);
if (len < 0) {
aa_put_ns(current_ns);
return len;
}
- (*string)[len] = '\n';
- (*string)[len + 1] = 0;
+ if (newline) {
+ (*string)[len] = '\n';
+ (*string)[++len] = 0;
+ }
aa_put_ns(current_ns);
- return len + 1;
+ return len;
}
/**
diff --git a/security/security.c b/security/security.c
index ed20d4c6ed93..691748cf1c50 100644
--- a/security/security.c
+++ b/security/security.c
@@ -754,6 +754,42 @@ static void __init lsm_early_task(struct task_struct *task)
panic("%s: Early task alloc failed.\n", __func__);
}
+/**
+ * append_ctx - append a lsm/context pair to a compound context
+ * @ctx: the existing compound context
+ * @ctxlen: size of the old context, including terminating nul byte
+ * @lsm: new lsm name, nul terminated
+ * @new: new context, possibly nul terminated
+ * @newlen: maximum size of @new
+ *
+ * replace @ctx with a new compound context, appending @newlsm and @new
+ * to @ctx. On exit the new data replaces the old, which is freed.
+ * @ctxlen is set to the new size, which includes a trailing nul byte.
+ *
+ * Returns 0 on success, -ENOMEM if no memory is available.
+ */
+static int append_ctx(char **ctx, int *ctxlen, const char *lsm, char *new,
+ int newlen)
+{
+ char *final;
+ int llen;
+
+ llen = strlen(lsm) + 1;
+ newlen = strnlen(new, newlen) + 1;
+
+ final = kzalloc(*ctxlen + llen + newlen, GFP_KERNEL);
+ if (final == NULL)
+ return -ENOMEM;
+ if (*ctxlen)
+ memcpy(final, *ctx, *ctxlen);
+ memcpy(final + *ctxlen, lsm, llen);
+ memcpy(final + *ctxlen + llen, new, newlen);
+ kfree(*ctx);
+ *ctx = final;
+ *ctxlen = *ctxlen + llen + newlen;
+ return 0;
+}
+
/*
* The default value of the LSM hook is defined in linux/lsm_hook_defs.h and
* can be accessed with:
@@ -2092,6 +2128,10 @@ int security_getprocattr(struct task_struct *p, const char *lsm, char *name,
char **value)
{
struct security_hook_list *hp;
+ char *final = NULL;
+ char *cp;
+ int rc = 0;
+ int finallen = 0;
int display = lsm_task_display(current);
int slot = 0;
@@ -2119,6 +2159,29 @@ int security_getprocattr(struct task_struct *p, const char *lsm, char *name,
return -ENOMEM;
}
+ if (!strcmp(name, "context")) {
+ hlist_for_each_entry(hp, &security_hook_heads.getprocattr,
+ list) {
+ rc = hp->hook.getprocattr(p, "context", &cp);
+ if (rc == -EINVAL)
+ continue;
+ if (rc < 0) {
+ kfree(final);
+ return rc;
+ }
+ rc = append_ctx(&final, &finallen, hp->lsmid->lsm,
+ cp, rc);
+ if (rc < 0) {
+ kfree(final);
+ return rc;
+ }
+ }
+ if (final == NULL)
+ return -EINVAL;
+ *value = final;
+ return finallen;
+ }
+
hlist_for_each_entry(hp, &security_hook_heads.getprocattr, list) {
if (lsm != NULL && strcmp(lsm, hp->lsmid->lsm))
continue;
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index c13b130bda55..5a128f1f30be 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -6290,7 +6290,7 @@ static int selinux_getprocattr(struct task_struct *p,
goto bad;
}
- if (!strcmp(name, "current"))
+ if (!strcmp(name, "current") || !strcmp(name, "context"))
sid = __tsec->sid;
else if (!strcmp(name, "prev"))
sid = __tsec->osid;
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 5bee05bd7a42..453923eee950 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -3479,7 +3479,7 @@ 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 && strcmp(name, "context") != 0)
return -EINVAL;
cp = kstrdup(skp->smk_known, GFP_KERNEL);
--
2.24.1
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