[PATCH 10/38] smack: Implement filesystem context security hooks [ver #10]

David Howells
2018-07-27T17:32:37Z

Implement filesystem context security hooks for the smack LSM.

Question: Should the ->fs_context_parse_source() hook be implemented to
check the labels on any source devices specified?

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Casey Schaufler <casey@schaufler-ca.com>
cc: linux-security-module@vger.kernel.org
---

security/smack/smack.h | 11 +
security/smack/smack_lsm.c | 337 ++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 343 insertions(+), 5 deletions(-)

diff --git a/security/smack/smack.h b/security/smack/smack.h
index f7db791fb566..e6d54e829394 100644
--- a/security/smack/smack.h
+++ b/security/smack/smack.h
@@ -195,11 +195,12 @@ struct smack_known_list_elem {

enum {
Opt_error = -1,
- Opt_fsdefault = 1,
- Opt_fsfloor = 2,
- Opt_fshat = 3,
- Opt_fsroot = 4,
- Opt_fstransmute = 5,
+ Opt_fsdefault = 0,
+ Opt_fsfloor = 1,
+ Opt_fshat = 2,
+ Opt_fsroot = 3,
+ Opt_fstransmute = 4,
+ nr__smack_params
};

/*
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 9811476c8441..339ac4d42785 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -42,6 +42,8 @@
#include <linux/shm.h>
#include <linux/binfmts.h>
#include <linux/parser.h>
+#include <linux/fs_context.h>
+#include <linux/fs_parser.h>
#include "smack.h"

#define TRANS_TRUE "TRUE"
@@ -521,6 +523,334 @@ static int smack_syslog(int typefrom_file)
return rc;
}

+/*
+ * Mount context operations
+ */
+
+struct smack_fs_context {
+ union {
+ struct {
+ char *fsdefault;
+ char *fsfloor;
+ char *fshat;
+ char *fsroot;
+ char *fstransmute;
+ };
+ char *ptrs[5];
+
+ };
+ struct superblock_smack *sbsp;
+ struct inode_smack *isp;
+ bool transmute;
+};
+
+/**
+ * smack_fs_context_free - Free the security data from a filesystem context
+ * @fc: The filesystem context to be cleaned up.
+ */
+static void smack_fs_context_free(struct fs_context *fc)
+{
+ struct smack_fs_context *ctx = fc->security;
+ int i;
+
+ if (ctx) {
+ for (i = 0; i < ARRAY_SIZE(ctx->ptrs); i++)
+ kfree(ctx->ptrs[i]);
+ kfree(ctx->isp);
+ kfree(ctx->sbsp);
+ kfree(ctx);
+ fc->security = NULL;
+ }
+}
+
+/**
+ * smack_fs_context_alloc - Allocate security data for a filesystem context
+ * @fc: The filesystem context.
+ * @reference: Reference dentry (automount/reconfigure) or NULL
+ *
+ * Returns 0 on success or -ENOMEM on error.
+ */
+static int smack_fs_context_alloc(struct fs_context *fc,
+ struct dentry *reference)
+{
+ struct smack_fs_context *ctx;
+ struct superblock_smack *sbsp;
+ struct inode_smack *isp;
+ struct smack_known *skp;
+
+ ctx = kzalloc(sizeof(struct smack_fs_context), GFP_KERNEL);
+ if (!ctx)
+ goto nomem;
+ fc->security = ctx;
+
+ sbsp = kzalloc(sizeof(struct superblock_smack), GFP_KERNEL);
+ if (!sbsp)
+ goto nomem_free;
+ ctx->sbsp = sbsp;
+
+ isp = new_inode_smack(NULL);
+ if (!isp)
+ goto nomem_free;
+ ctx->isp = isp;
+
+ if (reference) {
+ if (reference->d_sb->s_security)
+ memcpy(sbsp, reference->d_sb->s_security, sizeof(*sbsp));
+ } else if (!smack_privileged(CAP_MAC_ADMIN)) {
+ /* Unprivileged mounts get root and default from the caller. */
+ skp = smk_of_current();
+ sbsp->smk_root = skp;
+ sbsp->smk_default = skp;
+ } else {
+ sbsp->smk_root = &smack_known_floor;
+ sbsp->smk_default = &smack_known_floor;
+ sbsp->smk_floor = &smack_known_floor;
+ sbsp->smk_hat = &smack_known_hat;
+ /* SMK_SB_INITIALIZED will be zero from kzalloc. */
+ }
+
+ return 0;
+
+nomem_free:
+ smack_fs_context_free(fc);
+nomem:
+ return -ENOMEM;
+}
+
+/**
+ * smack_fs_context_dup - Duplicate the security data on fs_context duplication
+ * @fc: The new filesystem context.
+ * @src_fc: The source filesystem context being duplicated.
+ *
+ * Returns 0 on success or -ENOMEM on error.
+ */
+static int smack_fs_context_dup(struct fs_context *fc,
+ struct fs_context *src_fc)
+{
+ struct smack_fs_context *dst, *src = src_fc->security;
+ int i;
+
+ dst = kzalloc(sizeof(struct smack_fs_context), GFP_KERNEL);
+ if (!dst)
+ goto nomem;
+ fc->security = dst;
+
+ dst->sbsp = kmemdup(src->sbsp, sizeof(struct superblock_smack),
+ GFP_KERNEL);
+ if (!dst->sbsp)
+ goto nomem_free;
+
+ for (i = 0; i < ARRAY_SIZE(dst->ptrs); i++) {
+ if (src->ptrs[i]) {
+ dst->ptrs[i] = kstrdup(src->ptrs[i], GFP_KERNEL);
+ if (!dst->ptrs[i])
+ goto nomem_free;
+ }
+ }
+
+ return 0;
+
+nomem_free:
+ smack_fs_context_free(fc);
+nomem:
+ return -ENOMEM;
+}
+
+static const struct fs_parameter_spec smack_param_specs[nr__smack_params] = {
+ [Opt_fsdefault] = { fs_param_is_string },
+ [Opt_fsfloor] = { fs_param_is_string },
+ [Opt_fshat] = { fs_param_is_string },
+ [Opt_fsroot] = { fs_param_is_string },
+ [Opt_fstransmute] = { fs_param_is_string },
+};
+
+static const struct constant_table smack_param_keys[] = {
+ { SMK_FSDEFAULT, Opt_fsdefault },
+ { SMK_FSFLOOR, Opt_fsfloor },
+ { SMK_FSHAT, Opt_fshat },
+ { SMK_FSROOT, Opt_fsroot },
+ { SMK_FSTRANS, Opt_fstransmute },
+};
+
+static const struct fs_parameter_description smack_fs_parameters = {
+ .name = "smack",
+ .nr_params = nr__smack_params,
+ .nr_keys = ARRAY_SIZE(smack_param_keys),
+ .keys = smack_param_keys,
+ .specs = smack_param_specs,
+};
+
+/**
+ * smack_fs_context_parse_param - Parse a single mount parameter
+ * @fc: The new filesystem context being constructed.
+ * @param: The parameter.
+ *
+ * Returns 0 on success or -ENOMEM on error.
+ */
+static int smack_fs_context_parse_param(struct fs_context *fc,
+ struct fs_parameter *param)
+{
+ struct smack_fs_context *ctx = fc->security;
+ struct fs_parse_result result;
+ int ret;
+
+ /* Unprivileged mounts don't get to specify Smack values. */
+ if (!smack_privileged(CAP_MAC_ADMIN))
+ return -EPERM;
+
+ ret = fs_parse(fc, &smack_fs_parameters, param, &result);
+ if (ret <= 0)
+ return ret; /* Note: 0 indicates no match */
+
+ switch (result.key) {
+ case Opt_fsdefault:
+ if (ctx->fsdefault)
+ goto error_dup;
+ ctx->fsdefault = param->string;
+ if (!ctx->fsdefault)
+ goto error;
+ break;
+ case Opt_fsfloor:
+ if (ctx->fsfloor)
+ goto error_dup;
+ ctx->fsfloor = param->string;
+ if (!ctx->fsfloor)
+ goto error;
+ break;
+ case Opt_fshat:
+ if (ctx->fshat)
+ goto error_dup;
+ ctx->fshat = param->string;
+ if (!ctx->fshat)
+ goto error;
+ break;
+ case Opt_fsroot:
+ if (ctx->fsroot)
+ goto error_dup;
+ ctx->fsroot = param->string;
+ if (!ctx->fsroot)
+ goto error;
+ break;
+ case Opt_fstransmute:
+ if (ctx->fstransmute)
+ goto error_dup;
+ ctx->fstransmute = param->string;
+ if (!ctx->fstransmute)
+ goto error;
+ break;
+ default:
+ pr_warn("Smack: unknown mount option\n");
+ goto error_inval;
+ }
+
+ param->string = NULL;
+ return 0;
+
+error_dup:
+ warnf(fc, "Smack: duplicate mount option\n");
+error_inval:
+ ret = -EINVAL;
+error:
+ return ret;
+}
+
+/**
+ * smack_fs_context_validate - Validate the filesystem context security data
+ * @fc: The filesystem context.
+ *
+ * Returns 0 on success or -ENOMEM on error.
+ */
+static int smack_fs_context_validate(struct fs_context *fc)
+{
+ struct smack_fs_context *ctx = fc->security;
+ struct superblock_smack *sbsp = ctx->sbsp;
+ struct inode_smack *isp = ctx->isp;
+ struct smack_known *skp;
+
+ if (ctx->fsdefault) {
+ skp = smk_import_entry(ctx->fsdefault, 0);
+ if (IS_ERR(skp))
+ return PTR_ERR(skp);
+ sbsp->smk_default = skp;
+ }
+
+ if (ctx->fsfloor) {
+ skp = smk_import_entry(ctx->fsfloor, 0);
+ if (IS_ERR(skp))
+ return PTR_ERR(skp);
+ sbsp->smk_floor = skp;
+ }
+
+ if (ctx->fshat) {
+ skp = smk_import_entry(ctx->fshat, 0);
+ if (IS_ERR(skp))
+ return PTR_ERR(skp);
+ sbsp->smk_hat = skp;
+ }
+
+ if (ctx->fsroot || ctx->fstransmute) {
+ skp = smk_import_entry(ctx->fstransmute ?: ctx->fsroot, 0);
+ if (IS_ERR(skp))
+ return PTR_ERR(skp);
+ sbsp->smk_root = skp;
+ ctx->transmute = !!ctx->fstransmute;
+ }
+
+ isp->smk_inode = sbsp->smk_root;
+ return 0;
+}
+
+/**
+ * smack_sb_get_tree - Assign the context to a newly created superblock
+ * @fc: The new filesystem context.
+ *
+ * Returns 0 on success or -ENOMEM on error.
+ */
+static int smack_sb_get_tree(struct fs_context *fc)
+{
+ struct smack_fs_context *ctx = fc->security;
+ struct superblock_smack *sbsp = ctx->sbsp;
+ struct dentry *root = fc->root;
+ struct inode *inode = d_backing_inode(root);
+ struct super_block *sb = root->d_sb;
+ struct inode_smack *isp;
+ bool transmute = ctx->transmute;
+
+ if (sb->s_security)
+ return 0;
+
+ if (!smack_privileged(CAP_MAC_ADMIN)) {
+ /*
+ * For a handful of fs types with no user-controlled
+ * backing store it's okay to trust security labels
+ * in the filesystem. The rest are untrusted.
+ */
+ if (fc->user_ns != &init_user_ns &&
+ sb->s_magic != SYSFS_MAGIC && sb->s_magic != TMPFS_MAGIC &&
+ sb->s_magic != RAMFS_MAGIC) {
+ transmute = true;
+ sbsp->smk_flags |= SMK_SB_UNTRUSTED;
+ }
+ }
+
+ sbsp->smk_flags |= SMK_SB_INITIALIZED;
+ sb->s_security = sbsp;
+ ctx->sbsp = NULL;
+
+ /* Initialize the root inode. */
+ isp = inode->i_security;
+ if (isp == NULL) {
+ isp = ctx->isp;
+ ctx->isp = NULL;
+ inode->i_security = isp;
+ } else
+ isp->smk_inode = sbsp->smk_root;
+
+ if (transmute)
+ isp->smk_flags |= SMK_INODE_TRANSMUTE;
+
+ return 0;
+}

/*
* Superblock Hooks.
@@ -4649,6 +4979,13 @@ static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
LSM_HOOK_INIT(ptrace_traceme, smack_ptrace_traceme),
LSM_HOOK_INIT(syslog, smack_syslog),

+ LSM_HOOK_INIT(fs_context_alloc, smack_fs_context_alloc),
+ LSM_HOOK_INIT(fs_context_dup, smack_fs_context_dup),
+ LSM_HOOK_INIT(fs_context_free, smack_fs_context_free),
+ LSM_HOOK_INIT(fs_context_parse_param, smack_fs_context_parse_param),
+ LSM_HOOK_INIT(fs_context_validate, smack_fs_context_validate),
+ LSM_HOOK_INIT(sb_get_tree, smack_sb_get_tree),
+
LSM_HOOK_INIT(sb_alloc_security, smack_sb_alloc_security),
LSM_HOOK_INIT(sb_free_security, smack_sb_free_security),
LSM_HOOK_INIT(sb_copy_data, smack_sb_copy_data),