@@ -484,6 +484,55 @@ static int selinux_is_sblabel_mnt(struct super_block *sb)
}
}
+static int sb_check_xattr_support(struct super_block *sb)
+{
+ struct superblock_security_struct *sbsec = sb->s_security;
+ struct dentry *root = sb->s_root;
+ struct inode *root_inode = d_backing_inode(root);
+ u32 sid;
+ int rc;
+
+ /*
+ * Make sure that the xattr handler exists and that no
+ * error other than -ENODATA is returned by getxattr on
+ * the root directory. -ENODATA is ok, as this may be
+ * the first boot of the SELinux kernel before we have
+ * assigned xattr values to the filesystem.
+ */
+ if (!(root_inode->i_opflags & IOP_XATTR)) {
+ pr_warn("SELinux: (dev %s, type %s) has no xattr support\n",
+ sb->s_id, sb->s_type->name);
+ goto fallback;
+ }
+
+ rc = __vfs_getxattr(root, root_inode, XATTR_NAME_SELINUX, NULL, 0);
+ if (rc < 0 && rc != -ENODATA) {
+ if (rc == -EOPNOTSUPP) {
+ pr_warn("SELinux: (dev %s, type %s) has no security xattr handler\n",
+ sb->s_id, sb->s_type->name);
+ goto fallback;
+ } else {
+ pr_warn("SELinux: (dev %s, type %s) getxattr errno %d\n",
+ sb->s_id, sb->s_type->name, -rc);
+ return rc;
+ }
+ }
+ return 0;
+
+fallback:
+ /* No xattr support - try to fallback to genfs if possible. */
+ rc = security_genfs_sid(&selinux_state, sb->s_type->name, "/",
+ SECCLASS_DIR, &sid);
+ if (rc)
+ return -EOPNOTSUPP;
+
+ pr_warn("SELinux: (dev %s, type %s) falling back to genfs\n",
+ sb->s_id, sb->s_type->name);
+ sbsec->behavior = SECURITY_FS_USE_GENFS;
+ sbsec->sid = sid;
+ return 0;
+}
+
static int sb_finish_set_opts(struct super_block *sb)
{
struct superblock_security_struct *sbsec = sb->s_security;
@@ -492,30 +541,9 @@ static int sb_finish_set_opts(struct super_block *sb)
int rc = 0;
if (sbsec->behavior == SECURITY_FS_USE_XATTR) {
- /* Make sure that the xattr handler exists and that no
- error other than -ENODATA is returned by getxattr on
- the root directory. -ENODATA is ok, as this may be
- the first boot of the SELinux kernel before we have
- assigned xattr values to the filesystem. */
- if (!(root_inode->i_opflags & IOP_XATTR)) {
- pr_warn("SELinux: (dev %s, type %s) has no "
- "xattr support\n", sb->s_id, sb->s_type->name);
- rc = -EOPNOTSUPP;
- goto out;
- }
-
- rc = __vfs_getxattr(root, root_inode, XATTR_NAME_SELINUX, NULL, 0);
- if (rc < 0 && rc != -ENODATA) {
- if (rc == -EOPNOTSUPP)
- pr_warn("SELinux: (dev %s, type "
- "%s) has no security xattr handler\n",
- sb->s_id, sb->s_type->name);
- else
- pr_warn("SELinux: (dev %s, type "
- "%s) getxattr errno %d\n", sb->s_id,
- sb->s_type->name, -rc);
- goto out;
- }
+ rc = sb_check_xattr_support(sb);
+ if (rc)
+ return rc;
}
sbsec->flags |= SE_SBINITIALIZED;
@@ -554,7 +582,6 @@ static int sb_finish_set_opts(struct super_block *sb)
spin_lock(&sbsec->isec_lock);
}
spin_unlock(&sbsec->isec_lock);
-out:
return rc;
}
When a superblock is assigned the SECURITY_FS_USE_XATTR behavior by the policy yet it lacks xattr support, try to fall back to genfs rather than rejecting the mount. If a genfscon rule is found for the filesystem, then change the behavior to SECURITY_FS_USE_GENFS, otherwise reject the mount as before. A similar fallback is already done in security_fs_use() if no behavior specification is found for the given filesystem. This is needed e.g. for virtiofs, which may or may not support xattrs depending on the backing host filesystem. Example: # seinfo --genfs | grep ' ramfs' genfscon ramfs / system_u:object_r:ramfs_t:s0 # echo '(fsuse xattr ramfs (system_u object_r fs_t ((s0) (s0))))' >ramfs_xattr.cil # semodule -i ramfs_xattr.cil # mount -t ramfs none /mnt Before: mount: /mnt: mount(2) system call failed: Operation not supported. After: (mount succeeds) # ls -Zd /mnt system_u:object_r:ramfs_t:s0 /mnt See also: https://lore.kernel.org/selinux/20210105142148.GA3200@redhat.com/T/ https://github.com/fedora-selinux/selinux-policy/pull/478 Cc: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com> --- v2: - incorporated Paul's suggestions - corrected the `ls` command in reproducer security/selinux/hooks.c | 77 +++++++++++++++++++++++++++------------- 1 file changed, 52 insertions(+), 25 deletions(-)