[PATCH v30 05/12] LSM: Infrastructure management of the superblock

Mickaël Salaün
2021-03-16T20:44:01Z

From: Casey Schaufler <casey@schaufler-ca.com>

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.

Cc: Kees Cook <keescook@chromium.org>
Cc: John Johansen <john.johansen@canonical.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
Reviewed-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
Link: https://lore.kernel.org/r/20210316204252.427806-6-mic@digikod.net
---

Changes since v28:
* Add Acked-by Serge Hallyn.

Changes since v26:
* Rebase on commit b159e86b5a2a ("selinux: drop super_block backpointer
from superblock_security_struct"). No change in the patch itself,
only a trivial conflict because of an updated nearby line in
selinux_set_mnt_opts() variable declarations.

Changes since v20:
* Remove all Reviewed-by except Stephen Smalley:
https://lore.kernel.org/lkml/CAEjxPJ7ARJO57MBW66=xsBzMMRb=9uLgqocK5eskHCaiVMx7Vw@mail.gmail.com/
* Cosmetic fix in the commit message.

Changes since v17:
* Rebase the original LSM stacking patch from v5.3 to v5.7: I fixed some
diff conflicts caused by code moves and function renames in
selinux/include/objsec.h and selinux/hooks.c . I checked that it
builds but I didn't test the changes for SELinux nor SMACK.
https://lore.kernel.org/r/20190829232935.7099-2-casey@schaufler-ca.com
---
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 fb7f3193753d..75715998a95f 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1573,6 +1573,7 @@ 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 5ac96b16f8fa..e9c29480eb18 100644
--- a/security/security.c
+++ b/security/security.c
@@ -203,6 +203,7 @@ 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);
}

@@ -333,12 +334,13 @@ 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
@@ -670,6 +672,27 @@ 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.
+ */
+static 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;
+}
+
/*
* The default value of the LSM hook is defined in linux/lsm_hook_defs.h and
* can be accessed with:
@@ -867,12 +890,21 @@ 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 ddd097790d47..2ed9c995263a 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -322,7 +322,7 @@ 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
@@ -340,13 +340,6 @@ static void inode_free_security(struct inode *inode)
}
}

-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;
};
@@ -458,7 +451,7 @@ 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 +528,7 @@ static int sb_check_xattr_support(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;
@@ -626,7 +619,7 @@ 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 = sb->s_root;
struct selinux_mnt_opts *opts = mnt_opts;
struct inode_security_struct *root_isec;
@@ -863,8 +856,8 @@ 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;

@@ -896,8 +889,9 @@ 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);
@@ -1076,7 +1070,7 @@ 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))
@@ -1427,7 +1421,7 @@ 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
@@ -1778,7 +1772,8 @@ 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)) {
@@ -1809,7 +1804,7 @@ 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;

@@ -1958,7 +1953,7 @@ 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);
}
@@ -2587,11 +2582,7 @@ static void selinux_bprm_committed_creds(struct linux_binprm *bprm)

static int selinux_sb_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);
@@ -2599,16 +2590,10 @@ static int selinux_sb_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 selinux_sb_free_security(struct super_block *sb)
-{
- superblock_free_security(sb);
-}
-
static inline int opt_len(const char *s)
{
bool open_quote = false;
@@ -2687,7 +2672,7 @@ 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;

@@ -2925,7 +2910,7 @@ 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;

@@ -3227,7 +3212,7 @@ static int selinux_inode_setxattr(struct user_namespace *mnt_userns,
if (!selinux_initialized(&selinux_state))
return (inode_owner_or_capable(mnt_userns, inode) ? 0 : -EPERM);

- sbsec = inode->i_sb->s_security;
+ sbsec = selinux_superblock(inode->i_sb);
if (!(sbsec->flags & SBLABEL_MNT))
return -EOPNOTSUPP;

@@ -3472,13 +3457,14 @@ 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;

@@ -6975,6 +6961,7 @@ 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),
};

#ifdef CONFIG_PERF_EVENTS
@@ -7075,7 +7062,6 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
LSM_HOOK_INIT(bprm_committing_creds, selinux_bprm_committing_creds),
LSM_HOOK_INIT(bprm_committed_creds, selinux_bprm_committed_creds),

- LSM_HOOK_INIT(sb_free_security, selinux_sb_free_security),
LSM_HOOK_INIT(sb_free_mnt_opts, selinux_free_mnt_opts),
LSM_HOOK_INIT(sb_remount, selinux_sb_remount),
LSM_HOOK_INIT(sb_kern_mount, selinux_sb_kern_mount),
diff --git a/security/selinux/include/objsec.h b/security/selinux/include/objsec.h
index ca4d7ab6a835..2953132408bf 100644
--- a/security/selinux/include/objsec.h
+++ b/security/selinux/include/objsec.h
@@ -188,4 +188,10 @@ static inline u32 current_sid(void)
return tsec->sid;
}

+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 3438d0130378..9cea2e6c809f 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -47,6 +47,7 @@
#include <linux/sched.h>
#include <linux/audit.h>
#include <linux/vmalloc.h>
+#include <linux/lsm_hooks.h>
#include <net/netlabel.h>

#include "flask.h"
@@ -2875,7 +2876,7 @@ 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;

if (!selinux_initialized(state)) {
diff --git a/security/smack/smack.h b/security/smack/smack.h
index a9768b12716b..7077b18c79ec 100644
--- a/security/smack/smack.h
+++ b/security/smack/smack.h
@@ -357,6 +357,12 @@ 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 12a45e61c1a5..ee3e29603c9c 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -535,12 +535,7 @@ 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;
@@ -549,22 +544,10 @@ 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;
};
@@ -772,7 +755,7 @@ 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;
@@ -871,7 +854,7 @@ 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;

@@ -905,7 +888,7 @@ static int smack_bprm_creds_for_exec(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;
@@ -1157,7 +1140,7 @@ 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;
@@ -1400,7 +1383,7 @@ static int smack_inode_removexattr(struct user_namespace *mnt_userns,
*/
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)
@@ -1670,7 +1653,7 @@ 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;
@@ -3285,7 +3268,7 @@ static void smack_d_instantiate(struct dentry *opt_dentry, struct inode *inode)
return;

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.
@@ -4700,6 +4683,7 @@ 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 = {
@@ -4711,7 +4695,6 @@ 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),
--
2.30.2