Re: [PATCH 01/58] LSM: Infrastructure management of the superblock

[Kees Cook <keescook@chromium.org>]

On Fri, May 31, 2019 at 04:09:23PM -0700, Casey Schaufler wrote:
> Move management of the superblock->sb_security blob out
> of the individual security modules and into the security
> infrastructure. Instead of allocating the blobs from within
> the modules the modules tell the infrastructure how much
> space is required, and the space is allocated there.
> 
> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  include/linux/lsm_hooks.h         |  1 +
>  security/security.c               | 46 ++++++++++++++++++++----
>  security/selinux/hooks.c          | 58 ++++++++++++-------------------
>  security/selinux/include/objsec.h |  6 ++++
>  security/selinux/ss/services.c    |  3 +-
>  security/smack/smack.h            |  6 ++++
>  security/smack/smack_lsm.c        | 35 +++++--------------
>  7 files changed, 85 insertions(+), 70 deletions(-)
> 
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index a240a3fc5fc4..f9222a04968d 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -2047,6 +2047,7 @@ struct lsm_blob_sizes {
>  	int	lbs_cred;
>  	int	lbs_file;
>  	int	lbs_inode;
> +	int	lbs_superblock;
>  	int	lbs_ipc;
>  	int	lbs_msg_msg;
>  	int	lbs_task;
> diff --git a/security/security.c b/security/security.c
> index 23cbb1a295a3..550988a0f024 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -172,6 +172,7 @@ static void __init lsm_set_blob_sizes(struct lsm_blob_sizes *needed)
>  	lsm_set_blob_size(&needed->lbs_inode, &blob_sizes.lbs_inode);
>  	lsm_set_blob_size(&needed->lbs_ipc, &blob_sizes.lbs_ipc);
>  	lsm_set_blob_size(&needed->lbs_msg_msg, &blob_sizes.lbs_msg_msg);
> +	lsm_set_blob_size(&needed->lbs_superblock, &blob_sizes.lbs_superblock);
>  	lsm_set_blob_size(&needed->lbs_task, &blob_sizes.lbs_task);
>  }
>  
> @@ -300,12 +301,13 @@ static void __init ordered_lsm_init(void)
>  	for (lsm = ordered_lsms; *lsm; lsm++)
>  		prepare_lsm(*lsm);
>  
> -	init_debug("cred blob size     = %d\n", blob_sizes.lbs_cred);
> -	init_debug("file blob size     = %d\n", blob_sizes.lbs_file);
> -	init_debug("inode blob size    = %d\n", blob_sizes.lbs_inode);
> -	init_debug("ipc blob size      = %d\n", blob_sizes.lbs_ipc);
> -	init_debug("msg_msg blob size  = %d\n", blob_sizes.lbs_msg_msg);
> -	init_debug("task blob size     = %d\n", blob_sizes.lbs_task);
> +	init_debug("cred blob size       = %d\n", blob_sizes.lbs_cred);
> +	init_debug("file blob size       = %d\n", blob_sizes.lbs_file);
> +	init_debug("inode blob size      = %d\n", blob_sizes.lbs_inode);
> +	init_debug("ipc blob size        = %d\n", blob_sizes.lbs_ipc);
> +	init_debug("msg_msg blob size    = %d\n", blob_sizes.lbs_msg_msg);
> +	init_debug("superblock blob size = %d\n", blob_sizes.lbs_superblock);
> +	init_debug("task blob size       = %d\n", blob_sizes.lbs_task);
>  
>  	/*
>  	 * Create any kmem_caches needed for blobs
> @@ -603,6 +605,27 @@ static void __init lsm_early_task(struct task_struct *task)
>  		panic("%s: Early task alloc failed.\n", __func__);
>  }
>  
> +/**
> + * lsm_superblock_alloc - allocate a composite superblock blob
> + * @sb: the superblock that needs a blob
> + *
> + * Allocate the superblock blob for all the modules
> + *
> + * Returns 0, or -ENOMEM if memory can't be allocated.
> + */
> +int lsm_superblock_alloc(struct super_block *sb)
> +{
> +	if (blob_sizes.lbs_superblock == 0) {
> +		sb->s_security = NULL;
> +		return 0;
> +	}
> +
> +	sb->s_security = kzalloc(blob_sizes.lbs_superblock, GFP_KERNEL);
> +	if (sb->s_security == NULL)
> +		return -ENOMEM;
> +	return 0;
> +}
> +
>  /*
>   * Hook list operation macros.
>   *
> @@ -776,12 +799,21 @@ int security_fs_context_parse_param(struct fs_context *fc, struct fs_parameter *
>  
>  int security_sb_alloc(struct super_block *sb)
>  {
> -	return call_int_hook(sb_alloc_security, 0, sb);
> +	int rc = lsm_superblock_alloc(sb);
> +
> +	if (unlikely(rc))
> +		return rc;
> +	rc = call_int_hook(sb_alloc_security, 0, sb);
> +	if (unlikely(rc))
> +		security_sb_free(sb);
> +	return rc;
>  }
>  
>  void security_sb_free(struct super_block *sb)
>  {
>  	call_void_hook(sb_free_security, sb);
> +	kfree(sb->s_security);
> +	sb->s_security = NULL;
>  }
>  
>  void security_free_mnt_opts(void **mnt_opts)
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 1d0b37af2444..7478d8eda00a 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -335,7 +335,7 @@ static void inode_free_security(struct inode *inode)
>  
>  	if (!isec)
>  		return;
> -	sbsec = inode->i_sb->s_security;
> +	sbsec = selinux_superblock(inode->i_sb);
>  	/*
>  	 * As not all inode security structures are in a list, we check for
>  	 * empty list outside of the lock to make sure that we won't waste
> @@ -366,11 +366,7 @@ static int file_alloc_security(struct file *file)
>  
>  static int superblock_alloc_security(struct super_block *sb)
>  {
> -	struct superblock_security_struct *sbsec;
> -
> -	sbsec = kzalloc(sizeof(struct superblock_security_struct), GFP_KERNEL);
> -	if (!sbsec)
> -		return -ENOMEM;
> +	struct superblock_security_struct *sbsec = selinux_superblock(sb);
>  
>  	mutex_init(&sbsec->lock);
>  	INIT_LIST_HEAD(&sbsec->isec_head);
> @@ -379,18 +375,10 @@ static int superblock_alloc_security(struct super_block *sb)
>  	sbsec->sid = SECINITSID_UNLABELED;
>  	sbsec->def_sid = SECINITSID_FILE;
>  	sbsec->mntpoint_sid = SECINITSID_UNLABELED;
> -	sb->s_security = sbsec;
>  
>  	return 0;
>  }
>  
> -static void superblock_free_security(struct super_block *sb)
> -{
> -	struct superblock_security_struct *sbsec = sb->s_security;
> -	sb->s_security = NULL;
> -	kfree(sbsec);
> -}
> -
>  struct selinux_mnt_opts {
>  	const char *fscontext, *context, *rootcontext, *defcontext;
>  };
> @@ -507,7 +495,7 @@ static int selinux_is_genfs_special_handling(struct super_block *sb)
>  
>  static int selinux_is_sblabel_mnt(struct super_block *sb)
>  {
> -	struct superblock_security_struct *sbsec = sb->s_security;
> +	struct superblock_security_struct *sbsec = selinux_superblock(sb);
>  
>  	/*
>  	 * IMPORTANT: Double-check logic in this function when adding a new
> @@ -535,7 +523,7 @@ static int selinux_is_sblabel_mnt(struct super_block *sb)
>  
>  static int sb_finish_set_opts(struct super_block *sb)
>  {
> -	struct superblock_security_struct *sbsec = sb->s_security;
> +	struct superblock_security_struct *sbsec = selinux_superblock(sb);
>  	struct dentry *root = sb->s_root;
>  	struct inode *root_inode = d_backing_inode(root);
>  	int rc = 0;
> @@ -648,7 +636,7 @@ static int selinux_set_mnt_opts(struct super_block *sb,
>  				unsigned long *set_kern_flags)
>  {
>  	const struct cred *cred = current_cred();
> -	struct superblock_security_struct *sbsec = sb->s_security;
> +	struct superblock_security_struct *sbsec = selinux_superblock(sb);
>  	struct dentry *root = sbsec->sb->s_root;
>  	struct selinux_mnt_opts *opts = mnt_opts;
>  	struct inode_security_struct *root_isec;
> @@ -881,8 +869,8 @@ static int selinux_set_mnt_opts(struct super_block *sb,
>  static int selinux_cmp_sb_context(const struct super_block *oldsb,
>  				    const struct super_block *newsb)
>  {
> -	struct superblock_security_struct *old = oldsb->s_security;
> -	struct superblock_security_struct *new = newsb->s_security;
> +	struct superblock_security_struct *old = selinux_superblock(oldsb);
> +	struct superblock_security_struct *new = selinux_superblock(newsb);
>  	char oldflags = old->flags & SE_MNTMASK;
>  	char newflags = new->flags & SE_MNTMASK;
>  
> @@ -914,8 +902,9 @@ static int selinux_sb_clone_mnt_opts(const struct super_block *oldsb,
>  					unsigned long *set_kern_flags)
>  {
>  	int rc = 0;
> -	const struct superblock_security_struct *oldsbsec = oldsb->s_security;
> -	struct superblock_security_struct *newsbsec = newsb->s_security;
> +	const struct superblock_security_struct *oldsbsec =
> +						selinux_superblock(oldsb);
> +	struct superblock_security_struct *newsbsec = selinux_superblock(newsb);
>  
>  	int set_fscontext =	(oldsbsec->flags & FSCONTEXT_MNT);
>  	int set_context =	(oldsbsec->flags & CONTEXT_MNT);
> @@ -1085,7 +1074,7 @@ static int show_sid(struct seq_file *m, u32 sid)
>  
>  static int selinux_sb_show_options(struct seq_file *m, struct super_block *sb)
>  {
> -	struct superblock_security_struct *sbsec = sb->s_security;
> +	struct superblock_security_struct *sbsec = selinux_superblock(sb);
>  	int rc;
>  
>  	if (!(sbsec->flags & SE_SBINITIALIZED))
> @@ -1377,7 +1366,7 @@ static int inode_doinit_with_dentry(struct inode *inode, struct dentry *opt_dent
>  	if (isec->sclass == SECCLASS_FILE)
>  		isec->sclass = inode_mode_to_security_class(inode->i_mode);
>  
> -	sbsec = inode->i_sb->s_security;
> +	sbsec = selinux_superblock(inode->i_sb);
>  	if (!(sbsec->flags & SE_SBINITIALIZED)) {
>  		/* Defer initialization until selinux_complete_init,
>  		   after the initial policy is loaded and the security
> @@ -1767,7 +1756,8 @@ selinux_determine_inode_label(const struct task_security_struct *tsec,
>  				 const struct qstr *name, u16 tclass,
>  				 u32 *_new_isid)
>  {
> -	const struct superblock_security_struct *sbsec = dir->i_sb->s_security;
> +	const struct superblock_security_struct *sbsec =
> +						selinux_superblock(dir->i_sb);
>  
>  	if ((sbsec->flags & SE_SBINITIALIZED) &&
>  	    (sbsec->behavior == SECURITY_FS_USE_MNTPOINT)) {
> @@ -1798,7 +1788,7 @@ static int may_create(struct inode *dir,
>  	int rc;
>  
>  	dsec = inode_security(dir);
> -	sbsec = dir->i_sb->s_security;
> +	sbsec = selinux_superblock(dir->i_sb);
>  
>  	sid = tsec->sid;
>  
> @@ -1947,7 +1937,7 @@ static int superblock_has_perm(const struct cred *cred,
>  	struct superblock_security_struct *sbsec;
>  	u32 sid = cred_sid(cred);
>  
> -	sbsec = sb->s_security;
> +	sbsec = selinux_superblock(sb);
>  	return avc_has_perm(&selinux_state,
>  			    sid, sbsec->sid, SECCLASS_FILESYSTEM, perms, ad);
>  }
> @@ -2578,11 +2568,6 @@ static int selinux_sb_alloc_security(struct super_block *sb)
>  	return superblock_alloc_security(sb);
>  }
>  
> -static void selinux_sb_free_security(struct super_block *sb)
> -{
> -	superblock_free_security(sb);
> -}
> -
>  static inline int opt_len(const char *s)
>  {
>  	bool open_quote = false;
> @@ -2653,7 +2638,7 @@ static int selinux_sb_eat_lsm_opts(char *options, void **mnt_opts)
>  static int selinux_sb_remount(struct super_block *sb, void *mnt_opts)
>  {
>  	struct selinux_mnt_opts *opts = mnt_opts;
> -	struct superblock_security_struct *sbsec = sb->s_security;
> +	struct superblock_security_struct *sbsec = selinux_superblock(sb);
>  	u32 sid;
>  	int rc;
>  
> @@ -2877,7 +2862,7 @@ static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
>  	int rc;
>  	char *context;
>  
> -	sbsec = dir->i_sb->s_security;
> +	sbsec = selinux_superblock(dir->i_sb);
>  
>  	newsid = tsec->create_sid;
>  
> @@ -3115,7 +3100,7 @@ static int selinux_inode_setxattr(struct dentry *dentry, const char *name,
>  		return dentry_has_perm(current_cred(), dentry, FILE__SETATTR);
>  	}
>  
> -	sbsec = inode->i_sb->s_security;
> +	sbsec = selinux_superblock(inode->i_sb);
>  	if (!(sbsec->flags & SBLABEL_MNT))
>  		return -EOPNOTSUPP;
>  
> @@ -3296,13 +3281,14 @@ static int selinux_inode_setsecurity(struct inode *inode, const char *name,
>  				     const void *value, size_t size, int flags)
>  {
>  	struct inode_security_struct *isec = inode_security_novalidate(inode);
> -	struct superblock_security_struct *sbsec = inode->i_sb->s_security;
> +	struct superblock_security_struct *sbsec;
>  	u32 newsid;
>  	int rc;
>  
>  	if (strcmp(name, XATTR_SELINUX_SUFFIX))
>  		return -EOPNOTSUPP;
>  
> +	sbsec = selinux_superblock(inode->i_sb);
>  	if (!(sbsec->flags & SBLABEL_MNT))
>  		return -EOPNOTSUPP;
>  
> @@ -6647,6 +6633,7 @@ struct lsm_blob_sizes selinux_blob_sizes __lsm_ro_after_init = {
>  	.lbs_inode = sizeof(struct inode_security_struct),
>  	.lbs_ipc = sizeof(struct ipc_security_struct),
>  	.lbs_msg_msg = sizeof(struct msg_security_struct),
> +	.lbs_superblock = sizeof(struct superblock_security_struct),
>  };
>  
>  static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
> @@ -6675,7 +6662,6 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
>  	LSM_HOOK_INIT(fs_context_parse_param, selinux_fs_context_parse_param),
>  
>  	LSM_HOOK_INIT(sb_alloc_security, selinux_sb_alloc_security),
> -	LSM_HOOK_INIT(sb_free_security, selinux_sb_free_security),
>  	LSM_HOOK_INIT(sb_eat_lsm_opts, selinux_sb_eat_lsm_opts),
>  	LSM_HOOK_INIT(sb_free_mnt_opts, selinux_free_mnt_opts),
>  	LSM_HOOK_INIT(sb_remount, selinux_sb_remount),
> diff --git a/security/selinux/include/objsec.h b/security/selinux/include/objsec.h
> index 231262d8eac9..d08d7e5d2f93 100644
> --- a/security/selinux/include/objsec.h
> +++ b/security/selinux/include/objsec.h
> @@ -188,4 +188,10 @@ static inline struct ipc_security_struct *selinux_ipc(
>  	return ipc->security + selinux_blob_sizes.lbs_ipc;
>  }
>  
> +static inline struct superblock_security_struct *selinux_superblock(
> +					const struct super_block *superblock)
> +{
> +	return superblock->s_security + selinux_blob_sizes.lbs_superblock;
> +}
> +
>  #endif /* _SELINUX_OBJSEC_H_ */
> diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
> index ec62918521b1..e3f5d6aece66 100644
> --- a/security/selinux/ss/services.c
> +++ b/security/selinux/ss/services.c
> @@ -50,6 +50,7 @@
>  #include <linux/audit.h>
>  #include <linux/mutex.h>
>  #include <linux/vmalloc.h>
> +#include <linux/lsm_hooks.h>
>  #include <net/netlabel.h>
>  
>  #include "flask.h"
> @@ -2751,7 +2752,7 @@ int security_fs_use(struct selinux_state *state, struct super_block *sb)
>  	struct sidtab *sidtab;
>  	int rc = 0;
>  	struct ocontext *c;
> -	struct superblock_security_struct *sbsec = sb->s_security;
> +	struct superblock_security_struct *sbsec = selinux_superblock(sb);
>  	const char *fstype = sb->s_type->name;
>  
>  	read_lock(&state->ss->policy_rwlock);
> diff --git a/security/smack/smack.h b/security/smack/smack.h
> index cf52af77d15e..caecbcba9942 100644
> --- a/security/smack/smack.h
> +++ b/security/smack/smack.h
> @@ -375,6 +375,12 @@ static inline struct smack_known **smack_ipc(const struct kern_ipc_perm *ipc)
>  	return ipc->security + smack_blob_sizes.lbs_ipc;
>  }
>  
> +static inline struct superblock_smack *smack_superblock(
> +					const struct super_block *superblock)
> +{
> +	return superblock->s_security + smack_blob_sizes.lbs_superblock;
> +}
> +
>  /*
>   * Is the directory transmuting?
>   */
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index 5c1613519d5a..807eff2ccce9 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -540,12 +540,7 @@ static int smack_syslog(int typefrom_file)
>   */
>  static int smack_sb_alloc_security(struct super_block *sb)
>  {
> -	struct superblock_smack *sbsp;
> -
> -	sbsp = kzalloc(sizeof(struct superblock_smack), GFP_KERNEL);
> -
> -	if (sbsp == NULL)
> -		return -ENOMEM;
> +	struct superblock_smack *sbsp = smack_superblock(sb);
>  
>  	sbsp->smk_root = &smack_known_floor;
>  	sbsp->smk_default = &smack_known_floor;
> @@ -554,22 +549,10 @@ static int smack_sb_alloc_security(struct super_block *sb)
>  	/*
>  	 * SMK_SB_INITIALIZED will be zero from kzalloc.
>  	 */
> -	sb->s_security = sbsp;
>  
>  	return 0;
>  }
>  
> -/**
> - * smack_sb_free_security - free a superblock blob
> - * @sb: the superblock getting the blob
> - *
> - */
> -static void smack_sb_free_security(struct super_block *sb)
> -{
> -	kfree(sb->s_security);
> -	sb->s_security = NULL;
> -}
> -
>  struct smack_mnt_opts {
>  	const char *fsdefault, *fsfloor, *fshat, *fsroot, *fstransmute;
>  };
> @@ -781,7 +764,7 @@ static int smack_set_mnt_opts(struct super_block *sb,
>  {
>  	struct dentry *root = sb->s_root;
>  	struct inode *inode = d_backing_inode(root);
> -	struct superblock_smack *sp = sb->s_security;
> +	struct superblock_smack *sp = smack_superblock(sb);
>  	struct inode_smack *isp;
>  	struct smack_known *skp;
>  	struct smack_mnt_opts *opts = mnt_opts;
> @@ -880,7 +863,7 @@ static int smack_set_mnt_opts(struct super_block *sb,
>   */
>  static int smack_sb_statfs(struct dentry *dentry)
>  {
> -	struct superblock_smack *sbp = dentry->d_sb->s_security;
> +	struct superblock_smack *sbp = smack_superblock(dentry->d_sb);
>  	int rc;
>  	struct smk_audit_info ad;
>  
> @@ -917,7 +900,7 @@ static int smack_bprm_set_creds(struct linux_binprm *bprm)
>  	if (isp->smk_task == NULL || isp->smk_task == bsp->smk_task)
>  		return 0;
>  
> -	sbsp = inode->i_sb->s_security;
> +	sbsp = smack_superblock(inode->i_sb);
>  	if ((sbsp->smk_flags & SMK_SB_UNTRUSTED) &&
>  	    isp->smk_task != sbsp->smk_root)
>  		return 0;
> @@ -1168,7 +1151,7 @@ static int smack_inode_rename(struct inode *old_inode,
>   */
>  static int smack_inode_permission(struct inode *inode, int mask)
>  {
> -	struct superblock_smack *sbsp = inode->i_sb->s_security;
> +	struct superblock_smack *sbsp = smack_superblock(inode->i_sb);
>  	struct smk_audit_info ad;
>  	int no_block = mask & MAY_NOT_BLOCK;
>  	int rc;
> @@ -1410,7 +1393,7 @@ static int smack_inode_removexattr(struct dentry *dentry, const char *name)
>  	 */
>  	if (strcmp(name, XATTR_NAME_SMACK) == 0) {
>  		struct super_block *sbp = dentry->d_sb;
> -		struct superblock_smack *sbsp = sbp->s_security;
> +		struct superblock_smack *sbsp = smack_superblock(sbp);
>  
>  		isp->smk_inode = sbsp->smk_default;
>  	} else if (strcmp(name, XATTR_NAME_SMACKEXEC) == 0)
> @@ -1680,7 +1663,7 @@ static int smack_mmap_file(struct file *file,
>  	isp = smack_inode(file_inode(file));
>  	if (isp->smk_mmap == NULL)
>  		return 0;
> -	sbsp = file_inode(file)->i_sb->s_security;
> +	sbsp = smack_superblock(file_inode(file)->i_sb);
>  	if (sbsp->smk_flags & SMK_SB_UNTRUSTED &&
>  	    isp->smk_mmap != sbsp->smk_root)
>  		return -EACCES;
> @@ -3288,7 +3271,7 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
>  		goto unlockandout;
>  
>  	sbp = inode->i_sb;
> -	sbsp = sbp->s_security;
> +	sbsp = smack_superblock(sbp);
>  	/*
>  	 * We're going to use the superblock default label
>  	 * if there's no label on the file.
> @@ -4575,6 +4558,7 @@ struct lsm_blob_sizes smack_blob_sizes __lsm_ro_after_init = {
>  	.lbs_inode = sizeof(struct inode_smack),
>  	.lbs_ipc = sizeof(struct smack_known *),
>  	.lbs_msg_msg = sizeof(struct smack_known *),
> +	.lbs_superblock = sizeof(struct superblock_smack),
>  };
>  
>  static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
> @@ -4586,7 +4570,6 @@ static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
>  	LSM_HOOK_INIT(fs_context_parse_param, smack_fs_context_parse_param),
>  
>  	LSM_HOOK_INIT(sb_alloc_security, smack_sb_alloc_security),
> -	LSM_HOOK_INIT(sb_free_security, smack_sb_free_security),
>  	LSM_HOOK_INIT(sb_free_mnt_opts, smack_free_mnt_opts),
>  	LSM_HOOK_INIT(sb_eat_lsm_opts, smack_sb_eat_lsm_opts),
>  	LSM_HOOK_INIT(sb_statfs, smack_sb_statfs),
> -- 
> 2.19.1
> 

-- 
Kees Cook