selinux: try security xattr after genfs for kernfs filesystems

Since kernfs supports the security xattr handlers, we can simply use
these to determine the inode's context, dropping the need to update it
from kernfs explicitly using a security_inode_notifysecctx() call.

We achieve this by setting a new sbsec flag SE_SBGENFS_XATTR to all
mounts that are known to use kernfs under the hood and then fetching the
xattrs after determining the fallback genfs sid in
inode_doinit_with_dentry() when this flag is set.

This will allow implementing full security xattr support in kernfs and
removing the ...notifysecctx() call in a subsequent patch.

Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
[PM: more manual merge fixups]
Signed-off-by: Paul Moore <paul@paul-moore.com>

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 1d0b37a..085409b 100644 (file)
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -751,11 +751,13 @@ static int selinux_set_mnt_opts(struct super_block *sb,
 
        if (!strcmp(sb->s_type->name, "debugfs") ||
            !strcmp(sb->s_type->name, "tracefs") ||
-           !strcmp(sb->s_type->name, "sysfs") ||
-           !strcmp(sb->s_type->name, "pstore") ||
+           !strcmp(sb->s_type->name, "pstore"))
+               sbsec->flags |= SE_SBGENFS;
+
+       if (!strcmp(sb->s_type->name, "sysfs") ||
            !strcmp(sb->s_type->name, "cgroup") ||
            !strcmp(sb->s_type->name, "cgroup2"))
-               sbsec->flags |= SE_SBGENFS;
+               sbsec->flags |= SE_SBGENFS | SE_SBGENFS_XATTR;
 
        if (!sbsec->behavior) {
                /*
@@ -1354,6 +1356,67 @@ static int selinux_genfs_get_sid(struct dentry *dentry,
        return rc;
 }
 
+static int inode_doinit_use_xattr(struct inode *inode, struct dentry *dentry,
+                                 u32 def_sid, u32 *sid)
+{
+#define INITCONTEXTLEN 255
+       char *context;
+       unsigned int len;
+       int rc;
+
+       len = INITCONTEXTLEN;
+       context = kmalloc(len + 1, GFP_NOFS);
+       if (!context)
+               return -ENOMEM;
+
+       context[len] = '\0';
+       rc = __vfs_getxattr(dentry, inode, XATTR_NAME_SELINUX, context, len);
+       if (rc == -ERANGE) {
+               kfree(context);
+
+               /* Need a larger buffer.  Query for the right size. */
+               rc = __vfs_getxattr(dentry, inode, XATTR_NAME_SELINUX, NULL, 0);
+               if (rc < 0)
+                       return rc;
+
+               len = rc;
+               context = kmalloc(len + 1, GFP_NOFS);
+               if (!context)
+                       return -ENOMEM;
+
+               context[len] = '\0';
+               rc = __vfs_getxattr(dentry, inode, XATTR_NAME_SELINUX,
+                                   context, len);
+       }
+       if (rc < 0) {
+               kfree(context);
+               if (rc != -ENODATA) {
+                       pr_warn("SELinux: %s:  getxattr returned %d for dev=%s ino=%ld\n",
+                               __func__, -rc, inode->i_sb->s_id, inode->i_ino);
+                       return rc;
+               }
+               *sid = def_sid;
+               return 0;
+       }
+
+       rc = security_context_to_sid_default(&selinux_state, context, rc, sid,
+                                            def_sid, GFP_NOFS);
+       if (rc) {
+               char *dev = inode->i_sb->s_id;
+               unsigned long ino = inode->i_ino;
+
+               if (rc == -EINVAL) {
+                       pr_notice_ratelimited("SELinux: inode=%lu on dev=%s was found to have an invalid context=%s.  This indicates you may need to relabel the inode or the filesystem in question.\n",
+                                             ino, dev, context);
+               } else {
+                       pr_warn("SELinux: %s:  context_to_sid(%s) returned %d for dev=%s ino=%ld\n",
+                               __func__, context, -rc, dev, ino);
+               }
+       }
+       kfree(context);
+       return 0;
+}
+
 /* The inode's security attributes must be initialized before first use. */
 static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dentry)
 {
@@ -1362,9 +1425,6 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
        u32 task_sid, sid = 0;
        u16 sclass;
        struct dentry *dentry;
-#define INITCONTEXTLEN 255
-       char *context = NULL;
-       unsigned len = 0;
        int rc = 0;
 
        if (isec->initialized == LABEL_INITIALIZED)
@@ -1432,72 +1492,11 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
                        goto out;
                }
 
-               len = INITCONTEXTLEN;
-               context = kmalloc(len+1, GFP_NOFS);
-               if (!context) {
-                       rc = -ENOMEM;
-                       dput(dentry);
-                       goto out;
-               }
-               context[len] = '\0';
-               rc = __vfs_getxattr(dentry, inode, XATTR_NAME_SELINUX, context, len);
-               if (rc == -ERANGE) {
-                       kfree(context);
-
-                       /* Need a larger buffer.  Query for the right size. */
-                       rc = __vfs_getxattr(dentry, inode, XATTR_NAME_SELINUX, NULL, 0);
-                       if (rc < 0) {
-                               dput(dentry);
-                               goto out;
-                       }
-                       len = rc;
-                       context = kmalloc(len+1, GFP_NOFS);
-                       if (!context) {
-                               rc = -ENOMEM;
-                               dput(dentry);
-                               goto out;
-                       }
-                       context[len] = '\0';
-                       rc = __vfs_getxattr(dentry, inode, XATTR_NAME_SELINUX, context, len);
-               }
+               rc = inode_doinit_use_xattr(inode, dentry, sbsec->def_sid,
+                                           &sid);
                dput(dentry);
-               if (rc < 0) {
-                       if (rc != -ENODATA) {
-                               pr_warn("SELinux: %s:  getxattr returned "
-                                      "%d for dev=%s ino=%ld\n", __func__,
-                                      -rc, inode->i_sb->s_id, inode->i_ino);
-                               kfree(context);
-                               goto out;
-                       }
-                       /* Map ENODATA to the default file SID */
-                       sid = sbsec->def_sid;
-                       rc = 0;
-               } else {
-                       rc = security_context_to_sid_default(&selinux_state,
-                                                            context, rc, &sid,
-                                                            sbsec->def_sid,
-                                                            GFP_NOFS);
-                       if (rc) {
-                               char *dev = inode->i_sb->s_id;
-                               unsigned long ino = inode->i_ino;
-
-                               if (rc == -EINVAL) {
-                                       if (printk_ratelimit())
-                                               pr_notice("SELinux: inode=%lu on dev=%s was found to have an invalid "
-                                                       "context=%s.  This indicates you may need to relabel the inode or the "
-                                                       "filesystem in question.\n", ino, dev, context);
-                               } else {
-                                       pr_warn("SELinux: %s:  context_to_sid(%s) "
-                                              "returned %d for dev=%s ino=%ld\n",
-                                              __func__, context, -rc, dev, ino);
-                               }
-                               kfree(context);
-                               /* Leave with the unlabeled SID */
-                               rc = 0;
-                               break;
-                       }
-               }
-               kfree(context);
+               if (rc)
+                       goto out;
                break;
        case SECURITY_FS_USE_TASK:
                sid = task_sid;
@@ -1548,9 +1547,21 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
                                goto out;
                        rc = selinux_genfs_get_sid(dentry, sclass,
                                                   sbsec->flags, &sid);
-                       dput(dentry);
-                       if (rc)
+                       if (rc) {
+                               dput(dentry);
                                goto out;
+                       }
+
+                       if ((sbsec->flags & SE_SBGENFS_XATTR) &&
+                           (inode->i_opflags & IOP_XATTR)) {
+                               rc = inode_doinit_use_xattr(inode, dentry,
+                                                           sid, &sid);
+                               if (rc) {
+                                       dput(dentry);
+                                       goto out;
+                               }
+                       }
+                       dput(dentry);
                }
                break;
        }

diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
index b5b7c5a..1111212 100644 (file)
--- a/security/selinux/include/security.h
+++ b/security/selinux/include/security.h
@@ -58,6 +58,7 @@
 #define SE_SBINITIALIZED       0x0100
 #define SE_SBPROC              0x0200
 #define SE_SBGENFS             0x0400
+#define SE_SBGENFS_XATTR       0x0800
 
 #define CONTEXT_STR    "context"
 #define FSCONTEXT_STR  "fscontext"