AppArmor: file enforcement routines

AppArmor does files enforcement via pathname matching.  Matching is done
at file open using a dfa match engine.  Permission is against the final
file object not parent directories, ie. the traversal of directories
as part of the file match is implicitly allowed.  In the case of nonexistant
files (creation) permissions are checked against the target file not the
directory.  eg. In case of creating the file /dir/new, permissions are
checked against the match /dir/new not against /dir/.

The permissions for matches are currently stored in the dfa accept table,
but this will change to allow for dfa reuse and also to allow for sharing
of wider accept states.

Signed-off-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 457 insertions, 0 deletions

diff --git a/security/apparmor/file.c b/security/apparmor/file.c
new file mode 100644
index 000000000000..7312db741219
--- /dev/null
+++ b/security/apparmor/file.c
@@ -0,0 +1,457 @@
+/*
+ * AppArmor security module
+ *
+ * This file contains AppArmor mediation of files
+ *
+ * Copyright (C) 1998-2008 Novell/SUSE
+ * Copyright 2009-2010 Canonical Ltd.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation, version 2 of the
+ * License.
+ */
+
+#include "include/apparmor.h"
+#include "include/audit.h"
+#include "include/file.h"
+#include "include/match.h"
+#include "include/path.h"
+#include "include/policy.h"
+
+struct file_perms nullperms;
+
+
+/**
+ * audit_file_mask - convert mask to permission string
+ * @buffer: buffer to write string to (NOT NULL)
+ * @mask: permission mask to convert
+ */
+static void audit_file_mask(struct audit_buffer *ab, u32 mask)
+{
+        char str[10];
+
+        char *m = str;
+
+        if (mask & AA_EXEC_MMAP)
+                *m++ = 'm';
+        if (mask & (MAY_READ | AA_MAY_META_READ))
+                *m++ = 'r';
+        if (mask & (MAY_WRITE | AA_MAY_META_WRITE | AA_MAY_CHMOD |
+                    AA_MAY_CHOWN))
+                *m++ = 'w';
+        else if (mask & MAY_APPEND)
+                *m++ = 'a';
+        if (mask & AA_MAY_CREATE)
+                *m++ = 'c';
+        if (mask & AA_MAY_DELETE)
+                *m++ = 'd';
+        if (mask & AA_MAY_LINK)
+                *m++ = 'l';
+        if (mask & AA_MAY_LOCK)
+                *m++ = 'k';
+        if (mask & MAY_EXEC)
+                *m++ = 'x';
+        *m = '\0';
+
+        audit_log_string(ab, str);
+}
+
+/**
+ * file_audit_cb - call back for file specific audit fields
+ * @ab: audit_buffer  (NOT NULL)
+ * @va: audit struct to audit values of  (NOT NULL)
+ */
+static void file_audit_cb(struct audit_buffer *ab, void *va)
+{
+        struct common_audit_data *sa = va;
+        uid_t fsuid = current_fsuid();
+
+        if (sa->aad.fs.request & AA_AUDIT_FILE_MASK) {
+                audit_log_format(ab, " requested_mask=");
+                audit_file_mask(ab, sa->aad.fs.request);
+        }
+        if (sa->aad.fs.denied & AA_AUDIT_FILE_MASK) {
+                audit_log_format(ab, " denied_mask=");
+                audit_file_mask(ab, sa->aad.fs.denied);
+        }
+        if (sa->aad.fs.request & AA_AUDIT_FILE_MASK) {
+                audit_log_format(ab, " fsuid=%d", fsuid);
+                audit_log_format(ab, " ouid=%d", sa->aad.fs.ouid);
+        }
+
+        if (sa->aad.fs.target) {
+                audit_log_format(ab, " target=");
+                audit_log_untrustedstring(ab, sa->aad.fs.target);
+        }
+}
+
+/**
+ * aa_audit_file - handle the auditing of file operations
+ * @profile: the profile being enforced  (NOT NULL)
+ * @perms: the permissions computed for the request (NOT NULL)
+ * @gfp: allocation flags
+ * @op: operation being mediated
+ * @request: permissions requested
+ * @name: name of object being mediated (MAYBE NULL)
+ * @target: name of target (MAYBE NULL)
+ * @ouid: object uid
+ * @info: extra information message (MAYBE NULL)
+ * @error: 0 if operation allowed else failure error code
+ *
+ * Returns: %0 or error on failure
+ */
+int aa_audit_file(struct aa_profile *profile, struct file_perms *perms,
+                  gfp_t gfp, int op, u32 request, const char *name,
+                  const char *target, uid_t ouid, const char *info, int error)
+{
+        int type = AUDIT_APPARMOR_AUTO;
+        struct common_audit_data sa;
+        COMMON_AUDIT_DATA_INIT(&sa, NONE);
+        sa.aad.op = op,
+        sa.aad.fs.request = request;
+        sa.aad.name = name;
+        sa.aad.fs.target = target;
+        sa.aad.fs.ouid = ouid;
+        sa.aad.info = info;
+        sa.aad.error = error;
+
+        if (likely(!sa.aad.error)) {
+                u32 mask = perms->audit;
+
+                if (unlikely(AUDIT_MODE(profile) == AUDIT_ALL))
+                        mask = 0xffff;
+
+                /* mask off perms that are not being force audited */
+                sa.aad.fs.request &= mask;
+
+                if (likely(!sa.aad.fs.request))
+                        return 0;
+                type = AUDIT_APPARMOR_AUDIT;
+        } else {
+                /* only report permissions that were denied */
+                sa.aad.fs.request = sa.aad.fs.request & ~perms->allow;
+
+                if (sa.aad.fs.request & perms->kill)
+                        type = AUDIT_APPARMOR_KILL;
+
+                /* quiet known rejects, assumes quiet and kill do not overlap */
+                if ((sa.aad.fs.request & perms->quiet) &&
+                    AUDIT_MODE(profile) != AUDIT_NOQUIET &&
+                    AUDIT_MODE(profile) != AUDIT_ALL)
+                        sa.aad.fs.request &= ~perms->quiet;
+
+                if (!sa.aad.fs.request)
+                        return COMPLAIN_MODE(profile) ? 0 : sa.aad.error;
+        }
+
+        sa.aad.fs.denied = sa.aad.fs.request & ~perms->allow;
+        return aa_audit(type, profile, gfp, &sa, file_audit_cb);
+}
+
+/**
+ * map_old_perms - map old file perms layout to the new layout
+ * @old: permission set in old mapping
+ *
+ * Returns: new permission mapping
+ */
+static u32 map_old_perms(u32 old)
+{
+        u32 new = old & 0xf;
+        if (old & MAY_READ)
+                new |= AA_MAY_META_READ;
+        if (old & MAY_WRITE)
+                new |= AA_MAY_META_WRITE | AA_MAY_CREATE | AA_MAY_DELETE |
+                        AA_MAY_CHMOD | AA_MAY_CHOWN;
+        if (old & 0x10)
+                new |= AA_MAY_LINK;
+        /* the old mapping lock and link_subset flags where overlaid
+         * and use was determined by part of a pair that they were in
+         */
+        if (old & 0x20)
+                new |= AA_MAY_LOCK | AA_LINK_SUBSET;
+        if (old & 0x40) /* AA_EXEC_MMAP */
+                new |= AA_EXEC_MMAP;
+
+        new |= AA_MAY_META_READ;
+
+        return new;
+}
+
+/**
+ * compute_perms - convert dfa compressed perms to internal perms
+ * @dfa: dfa to compute perms for   (NOT NULL)
+ * @state: state in dfa
+ * @cond:  conditions to consider  (NOT NULL)
+ *
+ * TODO: convert from dfa + state to permission entry, do computation conversion
+ *       at load time.
+ *
+ * Returns: computed permission set
+ */
+static struct file_perms compute_perms(struct aa_dfa *dfa, unsigned int state,
+                                       struct path_cond *cond)
+{
+        struct file_perms perms;
+
+        /* FIXME: change over to new dfa format
+         * currently file perms are encoded in the dfa, new format
+         * splits the permissions from the dfa.  This mapping can be
+         * done at profile load
+         */
+        perms.kill = 0;
+
+        if (current_fsuid() == cond->uid) {
+                perms.allow = map_old_perms(dfa_user_allow(dfa, state));
+                perms.audit = map_old_perms(dfa_user_audit(dfa, state));
+                perms.quiet = map_old_perms(dfa_user_quiet(dfa, state));
+                perms.xindex = dfa_user_xindex(dfa, state);
+        } else {
+                perms.allow = map_old_perms(dfa_other_allow(dfa, state));
+                perms.audit = map_old_perms(dfa_other_audit(dfa, state));
+                perms.quiet = map_old_perms(dfa_other_quiet(dfa, state));
+                perms.xindex = dfa_other_xindex(dfa, state);
+        }
+
+        /* change_profile wasn't determined by ownership in old mapping */
+        if (ACCEPT_TABLE(dfa)[state] & 0x80000000)
+                perms.allow |= AA_MAY_CHANGE_PROFILE;
+
+        return perms;
+}
+
+/**
+ * aa_str_perms - find permission that match @name
+ * @dfa: to match against  (MAYBE NULL)
+ * @state: state to start matching in
+ * @name: string to match against dfa  (NOT NULL)
+ * @cond: conditions to consider for permission set computation  (NOT NULL)
+ * @perms: Returns - the permissions found when matching @name
+ *
+ * Returns: the final state in @dfa when beginning @start and walking @name
+ */
+unsigned int aa_str_perms(struct aa_dfa *dfa, unsigned int start,
+                          const char *name, struct path_cond *cond,
+                          struct file_perms *perms)
+{
+        unsigned int state;
+        if (!dfa) {
+                *perms = nullperms;
+                return DFA_NOMATCH;
+        }
+
+        state = aa_dfa_match(dfa, start, name);
+        *perms = compute_perms(dfa, state, cond);
+
+        return state;
+}
+
+/**
+ * is_deleted - test if a file has been completely unlinked
+ * @dentry: dentry of file to test for deletion  (NOT NULL)
+ *
+ * Returns: %1 if deleted else %0
+ */
+static inline bool is_deleted(struct dentry *dentry)
+{
+        if (d_unlinked(dentry) && dentry->d_inode->i_nlink == 0)
+                return 1;
+        return 0;
+}
+
+/**
+ * aa_path_perm - do permissions check & audit for @path
+ * @op: operation being checked
+ * @profile: profile being enforced  (NOT NULL)
+ * @path: path to check permissions of  (NOT NULL)
+ * @flags: any additional path flags beyond what the profile specifies
+ * @request: requested permissions
+ * @cond: conditional info for this request  (NOT NULL)
+ *
+ * Returns: %0 else error if access denied or other error
+ */
+int aa_path_perm(int op, struct aa_profile *profile, struct path *path,
+                 int flags, u32 request, struct path_cond *cond)
+{
+        char *buffer = NULL;
+        struct file_perms perms = {};
+        const char *name, *info = NULL;
+        int error;
+
+        flags |= profile->path_flags | (S_ISDIR(cond->mode) ? PATH_IS_DIR : 0);
+        error = aa_get_name(path, flags, &buffer, &name);
+        if (error) {
+                if (error == -ENOENT && is_deleted(path->dentry)) {
+                        /* Access to open files that are deleted are
+                         * give a pass (implicit delegation)
+                         */
+                        error = 0;
+                        perms.allow = request;
+                } else if (error == -ENOENT)
+                        info = "Failed name lookup - deleted entry";
+                else if (error == -ESTALE)
+                        info = "Failed name lookup - disconnected path";
+                else if (error == -ENAMETOOLONG)
+                        info = "Failed name lookup - name too long";
+                else
+                        info = "Failed name lookup";
+        } else {
+                aa_str_perms(profile->file.dfa, profile->file.start, name, cond,
+                             &perms);
+                if (request & ~perms.allow)
+                        error = -EACCES;
+        }
+        error = aa_audit_file(profile, &perms, GFP_KERNEL, op, request, name,
+                              NULL, cond->uid, info, error);
+        kfree(buffer);
+
+        return error;
+}
+
+/**
+ * xindex_is_subset - helper for aa_path_link
+ * @link: link permission set
+ * @target: target permission set
+ *
+ * test target x permissions are equal OR a subset of link x permissions
+ * this is done as part of the subset test, where a hardlink must have
+ * a subset of permissions that the target has.
+ *
+ * Returns: %1 if subset else %0
+ */
+static inline bool xindex_is_subset(u32 link, u32 target)
+{
+        if (((link & ~AA_X_UNSAFE) != (target & ~AA_X_UNSAFE)) ||
+            ((link & AA_X_UNSAFE) && !(target & AA_X_UNSAFE)))
+                return 0;
+
+        return 1;
+}
+
+/**
+ * aa_path_link - Handle hard link permission check
+ * @profile: the profile being enforced  (NOT NULL)
+ * @old_dentry: the target dentry  (NOT NULL)
+ * @new_dir: directory the new link will be created in  (NOT NULL)
+ * @new_dentry: the link being created  (NOT NULL)
+ *
+ * Handle the permission test for a link & target pair.  Permission
+ * is encoded as a pair where the link permission is determined
+ * first, and if allowed, the target is tested.  The target test
+ * is done from the point of the link match (not start of DFA)
+ * making the target permission dependent on the link permission match.
+ *
+ * The subset test if required forces that permissions granted
+ * on link are a subset of the permission granted to target.
+ *
+ * Returns: %0 if allowed else error
+ */
+int aa_path_link(struct aa_profile *profile, struct dentry *old_dentry,
+                 struct path *new_dir, struct dentry *new_dentry)
+{
+        struct path link = { new_dir->mnt, new_dentry };
+        struct path target = { new_dir->mnt, old_dentry };
+        struct path_cond cond = {
+                old_dentry->d_inode->i_uid,
+                old_dentry->d_inode->i_mode
+        };
+        char *buffer = NULL, *buffer2 = NULL;
+        const char *lname, *tname = NULL, *info = NULL;
+        struct file_perms lperms, perms;
+        u32 request = AA_MAY_LINK;
+        unsigned int state;
+        int error;
+
+        lperms = nullperms;
+
+        /* buffer freed below, lname is pointer in buffer */
+        error = aa_get_name(&link, profile->path_flags, &buffer, &lname);
+        if (error)
+                goto audit;
+
+        /* buffer2 freed below, tname is pointer in buffer2 */
+        error = aa_get_name(&target, profile->path_flags, &buffer2, &tname);
+        if (error)
+                goto audit;
+
+        error = -EACCES;
+        /* aa_str_perms - handles the case of the dfa being NULL */
+        state = aa_str_perms(profile->file.dfa, profile->file.start, lname,
+                             &cond, &lperms);
+
+        if (!(lperms.allow & AA_MAY_LINK))
+                goto audit;
+
+        /* test to see if target can be paired with link */
+        state = aa_dfa_null_transition(profile->file.dfa, state);
+        aa_str_perms(profile->file.dfa, state, tname, &cond, &perms);
+
+        /* force audit/quiet masks for link are stored in the second entry
+         * in the link pair.
+         */
+        lperms.audit = perms.audit;
+        lperms.quiet = perms.quiet;
+        lperms.kill = perms.kill;
+
+        if (!(perms.allow & AA_MAY_LINK)) {
+                info = "target restricted";
+                goto audit;
+        }
+
+        /* done if link subset test is not required */
+        if (!(perms.allow & AA_LINK_SUBSET))
+                goto done_tests;
+
+        /* Do link perm subset test requiring allowed permission on link are a
+         * subset of the allowed permissions on target.
+         */
+        aa_str_perms(profile->file.dfa, profile->file.start, tname, &cond,
+                     &perms);
+
+        /* AA_MAY_LINK is not considered in the subset test */
+        request = lperms.allow & ~AA_MAY_LINK;
+        lperms.allow &= perms.allow | AA_MAY_LINK;
+
+        request |= AA_AUDIT_FILE_MASK & (lperms.allow & ~perms.allow);
+        if (request & ~lperms.allow) {
+                goto audit;
+        } else if ((lperms.allow & MAY_EXEC) &&
+                   !xindex_is_subset(lperms.xindex, perms.xindex)) {
+                lperms.allow &= ~MAY_EXEC;
+                request |= MAY_EXEC;
+                info = "link not subset of target";
+                goto audit;
+        }
+
+done_tests:
+        error = 0;
+
+audit:
+        error = aa_audit_file(profile, &lperms, GFP_KERNEL, OP_LINK, request,
+                              lname, tname, cond.uid, info, error);
+        kfree(buffer);
+        kfree(buffer2);
+
+        return error;
+}
+
+/**
+ * aa_file_perm - do permission revalidation check & audit for @file
+ * @op: operation being checked
+ * @profile: profile being enforced   (NOT NULL)
+ * @file: file to revalidate access permissions on  (NOT NULL)
+ * @request: requested permissions
+ *
+ * Returns: %0 if access allowed else error
+ */
+int aa_file_perm(int op, struct aa_profile *profile, struct file *file,
+                 u32 request)
+{
+        struct path_cond cond = {
+                .uid = file->f_path.dentry->d_inode->i_uid,
+                .mode = file->f_path.dentry->d_inode->i_mode
+        };
+
+        return aa_path_perm(op, profile, &file->f_path, PATH_DELEGATE_DELETED,
+                            request, &cond);
+}