On Tue, Feb 02, 2021 at 05:27:03PM +0100, Mickaël Salaün wrote:
> From: Casey Schaufler <ca...@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 <keesc...@chromium.org>
> Cc: John Johansen <john.johan...@canonical.com>
> Signed-off-by: Casey Schaufler <ca...@schaufler-ca.com>
> Signed-off-by: Mickaël Salaün <m...@linux.microsoft.com>
> Reviewed-by: Stephen Smalley <stephen.smalley.w...@gmail.com>
Acked-by: Serge Hallyn <se...@hallyn.com>
I wonder how many out of tree modules this will impact :) Actually
if some new incoming module does an rcu callback to free the
sb_security, then the security_sb_free will need an update, but
that seems unlikely.
> ---
>
> 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=9ulgqock5eskhcaivmx...@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-ca...@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 a19adef1f088..970106d98306 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -1563,6 +1563,7 @@ 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 7b09cfbae94f..9f979d4afe6c 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 644b17ec9e63..ecf0ca8c3108 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
> @@ -486,7 +479,7 @@ 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;
> @@ -599,7 +592,7 @@ 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;
> @@ -836,8 +829,8 @@ 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;
>
> @@ -869,8 +862,9 @@ 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);
> @@ -1049,7 +1043,7 @@ 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))
> @@ -1399,7 +1393,7 @@ 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
> @@ -1750,7 +1744,8 @@ 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)) {
> @@ -1781,7 +1776,7 @@ 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;
>
> @@ -1930,7 +1925,7 @@ 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);
> }
> @@ -2559,11 +2554,7 @@ 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);
> @@ -2571,16 +2562,10 @@ 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;
> @@ -2659,7 +2644,7 @@ 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;
>
> @@ -2897,7 +2882,7 @@ 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;
>
> @@ -3142,7 +3127,7 @@ static int selinux_inode_setxattr(struct dentry
> *dentry, const char *name,
> if (!selinux_initialized(&selinux_state))
> return (inode_owner_or_capable(inode) ? 0 : -EPERM);
>
> - sbsec = inode->i_sb->s_security;
> + sbsec = selinux_superblock(inode->i_sb);
> if (!(sbsec->flags & SBLABEL_MNT))
> return -EOPNOTSUPP;
>
> @@ -3384,13 +3369,14 @@ 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;
>
> @@ -6882,6 +6868,7 @@ 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
> @@ -6982,7 +6969,6 @@ 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 597b79703584..74e3905dd9c5 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"
> @@ -2873,7 +2874,7 @@ 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 f69c3dd9a0c6..767084dc2c29 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;
> @@ -1398,7 +1381,7 @@ 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)
> @@ -1668,7 +1651,7 @@ 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;
> @@ -3283,7 +3266,7 @@ 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.
> @@ -4696,6 +4679,7 @@ 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 = {
> @@ -4707,7 +4691,6 @@ 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),
> --
> 2.30.0
