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Message-ID: <20241022161009.982584-11-mic@digikod.net>
Date: Tue, 22 Oct 2024 18:10:05 +0200
From: Mickaël Salaün <mic@...ikod.net>
To: Eric Paris <eparis@...hat.com>,
Paul Moore <paul@...l-moore.com>,
Günther Noack <gnoack@...gle.com>,
"Serge E . Hallyn" <serge@...lyn.com>
Cc: Mickaël Salaün <mic@...ikod.net>,
Ben Scarlato <akhna@...gle.com>,
Casey Schaufler <casey@...aufler-ca.com>,
Charles Zaffery <czaffery@...lox.com>,
James Morris <jmorris@...ei.org>,
Jann Horn <jannh@...gle.com>,
Jeff Xu <jeffxu@...gle.com>,
Jorge Lucangeli Obes <jorgelo@...gle.com>,
Kees Cook <kees@...nel.org>,
Konstantin Meskhidze <konstantin.meskhidze@...wei.com>,
Matt Bobrowski <mattbobrowski@...gle.com>,
Mikhail Ivanov <ivanov.mikhail1@...wei-partners.com>,
Praveen K Paladugu <prapal@...ux.microsoft.com>,
Robert Salvet <robert.salvet@...lox.com>,
Shervin Oloumi <enlightened@...gle.com>,
Song Liu <song@...nel.org>,
Tahera Fahimi <fahimitahera@...il.com>,
audit@...r.kernel.org,
linux-kernel@...r.kernel.org,
linux-security-module@...r.kernel.org
Subject: [RFC PATCH v2 10/14] landlock: Log file-related denials
Add audit support for path_mkdir, path_mknod, path_symlink, path_unlink,
path_rmdir, path_truncate, path_link, path_rename, and file_open hooks.
Audit record sample for a link action:
DENY: domain=4533720568 blockers=fs_refer path="/usr/bin" dev="vda2" ino=351
DOM_INFO: domain=4533720568 parent=0 pid=325 uid=0 exe="/root/sandboxer" comm="sandboxer"
DENY: domain=4533720568 blockers=fs_make_reg,fs_refer path="/usr/local" dev="vda2" ino=365
SYSCALL: arch=c000003e syscall=265 success=no exit=-13 ...
Cc: Günther Noack <gnoack@...gle.com>
Signed-off-by: Mickaël Salaün <mic@...ikod.net>
Link: https://lore.kernel.org/r/20241022161009.982584-11-mic@digikod.net
---
Changes since v2:
* Revamp logging and support the path_link and path_rename hooks.
* Add KUnit tests.
Changes since v1:
* Move audit code to the ptrace patch.
---
security/landlock/audit.c | 173 ++++++++++++++++++++++++++++++++++++--
security/landlock/audit.h | 9 ++
security/landlock/fs.c | 64 +++++++++++---
3 files changed, 229 insertions(+), 17 deletions(-)
diff --git a/security/landlock/audit.c b/security/landlock/audit.c
index 4cd9407459d2..9c8b6c246884 100644
--- a/security/landlock/audit.c
+++ b/security/landlock/audit.c
@@ -7,23 +7,55 @@
#include <kunit/test.h>
#include <linux/audit.h>
+#include <linux/bitops.h>
#include <linux/lsm_audit.h>
#include <linux/pid.h>
#include <linux/uidgid.h>
+#include <uapi/linux/landlock.h>
#include "audit.h"
+#include "common.h"
#include "cred.h"
#include "domain.h"
#include "ruleset.h"
-static const char *get_blocker(const enum landlock_request_type type)
+static const char *const fs_access_strings[] = {
+ [BIT_INDEX(LANDLOCK_ACCESS_FS_EXECUTE)] = "fs_execute",
+ [BIT_INDEX(LANDLOCK_ACCESS_FS_WRITE_FILE)] = "fs_write_file",
+ [BIT_INDEX(LANDLOCK_ACCESS_FS_READ_FILE)] = "fs_read_file",
+ [BIT_INDEX(LANDLOCK_ACCESS_FS_READ_DIR)] = "fs_read_dir",
+ [BIT_INDEX(LANDLOCK_ACCESS_FS_REMOVE_DIR)] = "fs_remove_dir",
+ [BIT_INDEX(LANDLOCK_ACCESS_FS_REMOVE_FILE)] = "fs_remove_file",
+ [BIT_INDEX(LANDLOCK_ACCESS_FS_MAKE_CHAR)] = "fs_make_char",
+ [BIT_INDEX(LANDLOCK_ACCESS_FS_MAKE_DIR)] = "fs_make_dir",
+ [BIT_INDEX(LANDLOCK_ACCESS_FS_MAKE_REG)] = "fs_make_reg",
+ [BIT_INDEX(LANDLOCK_ACCESS_FS_MAKE_SOCK)] = "fs_make_sock",
+ [BIT_INDEX(LANDLOCK_ACCESS_FS_MAKE_FIFO)] = "fs_make_fifo",
+ [BIT_INDEX(LANDLOCK_ACCESS_FS_MAKE_BLOCK)] = "fs_make_block",
+ [BIT_INDEX(LANDLOCK_ACCESS_FS_MAKE_SYM)] = "fs_make_sym",
+ [BIT_INDEX(LANDLOCK_ACCESS_FS_REFER)] = "fs_refer",
+ [BIT_INDEX(LANDLOCK_ACCESS_FS_TRUNCATE)] = "fs_truncate",
+ [BIT_INDEX(LANDLOCK_ACCESS_FS_IOCTL_DEV)] = "fs_ioctl_dev",
+};
+static_assert(ARRAY_SIZE(fs_access_strings) == LANDLOCK_NUM_ACCESS_FS);
+
+static __attribute_const__ const char *
+get_blocker(const enum landlock_request_type type,
+ const unsigned long access_bit)
{
switch (type) {
case LANDLOCK_REQUEST_PTRACE:
+ WARN_ON_ONCE(access_bit != -1);
return "ptrace";
case LANDLOCK_REQUEST_FS_CHANGE_LAYOUT:
+ WARN_ON_ONCE(access_bit != -1);
return "fs_change_layout";
+
+ case LANDLOCK_REQUEST_FS_ACCESS:
+ if (WARN_ON_ONCE(access_bit >= ARRAY_SIZE(fs_access_strings)))
+ return "unknown";
+ return fs_access_strings[access_bit];
}
WARN_ON_ONCE(1);
@@ -31,9 +63,20 @@ static const char *get_blocker(const enum landlock_request_type type)
}
static void log_blockers(struct audit_buffer *const ab,
- const enum landlock_request_type type)
+ const enum landlock_request_type type,
+ const access_mask_t access)
{
- audit_log_format(ab, "%s", get_blocker(type));
+ const unsigned long access_mask = access;
+ unsigned long access_bit;
+ size_t i = 0;
+
+ for_each_set_bit(access_bit, &access_mask, BITS_PER_TYPE(access)) {
+ audit_log_format(ab, "%s%s", (i == 0) ? "" : ",",
+ get_blocker(type, access_bit));
+ i++;
+ }
+ if (i == 0)
+ audit_log_format(ab, "%s", get_blocker(type, -1));
}
static void log_node(struct landlock_hierarchy *const node)
@@ -121,9 +164,110 @@ static void test_get_hierarchy(struct kunit *const test)
#endif /* CONFIG_SECURITY_LANDLOCK_KUNIT_TEST */
+static size_t get_denied_layer(const struct landlock_ruleset *const domain,
+ access_mask_t *const access_request,
+ const layer_mask_t (*const layer_masks)[],
+ const size_t layer_masks_size)
+{
+ const unsigned long access_req = *access_request;
+ unsigned long access_bit;
+ access_mask_t missing = 0;
+ long youngest_layer = -1;
+
+ for_each_set_bit(access_bit, &access_req, layer_masks_size) {
+ const access_mask_t mask = (*layer_masks)[access_bit];
+ long layer;
+
+ if (!mask)
+ continue;
+
+ /* __fls(1) == 0 */
+ layer = __fls(mask);
+ if (layer > youngest_layer) {
+ youngest_layer = layer;
+ missing = BIT(access_bit);
+ } else if (layer == youngest_layer) {
+ missing |= BIT(access_bit);
+ }
+ }
+
+ *access_request = missing;
+ if (youngest_layer == -1)
+ return domain->num_layers - 1;
+
+ return youngest_layer;
+}
+
+#ifdef CONFIG_SECURITY_LANDLOCK_KUNIT_TEST
+
+static void test_get_denied_layer(struct kunit *const test)
+{
+ const struct landlock_ruleset dom = {
+ .num_layers = 5,
+ };
+ const layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_FS] = {
+ [BIT_INDEX(LANDLOCK_ACCESS_FS_EXECUTE)] = BIT(0),
+ [BIT_INDEX(LANDLOCK_ACCESS_FS_READ_FILE)] = BIT(1),
+ [BIT_INDEX(LANDLOCK_ACCESS_FS_READ_DIR)] = BIT(1) | BIT(0),
+ [BIT_INDEX(LANDLOCK_ACCESS_FS_REMOVE_DIR)] = BIT(2),
+ };
+ access_mask_t access;
+
+ access = LANDLOCK_ACCESS_FS_EXECUTE;
+ KUNIT_EXPECT_EQ(test, 0,
+ get_denied_layer(&dom, &access, &layer_masks,
+ sizeof(layer_masks)));
+ KUNIT_EXPECT_EQ(test, access, LANDLOCK_ACCESS_FS_EXECUTE);
+
+ access = LANDLOCK_ACCESS_FS_READ_FILE;
+ KUNIT_EXPECT_EQ(test, 1,
+ get_denied_layer(&dom, &access, &layer_masks,
+ sizeof(layer_masks)));
+ KUNIT_EXPECT_EQ(test, access, LANDLOCK_ACCESS_FS_READ_FILE);
+
+ access = LANDLOCK_ACCESS_FS_READ_DIR;
+ KUNIT_EXPECT_EQ(test, 1,
+ get_denied_layer(&dom, &access, &layer_masks,
+ sizeof(layer_masks)));
+ KUNIT_EXPECT_EQ(test, access, LANDLOCK_ACCESS_FS_READ_DIR);
+
+ access = LANDLOCK_ACCESS_FS_READ_FILE | LANDLOCK_ACCESS_FS_READ_DIR;
+ KUNIT_EXPECT_EQ(test, 1,
+ get_denied_layer(&dom, &access, &layer_masks,
+ sizeof(layer_masks)));
+ KUNIT_EXPECT_EQ(test, access,
+ LANDLOCK_ACCESS_FS_READ_FILE |
+ LANDLOCK_ACCESS_FS_READ_DIR);
+
+ access = LANDLOCK_ACCESS_FS_EXECUTE | LANDLOCK_ACCESS_FS_READ_DIR;
+ KUNIT_EXPECT_EQ(test, 1,
+ get_denied_layer(&dom, &access, &layer_masks,
+ sizeof(layer_masks)));
+ KUNIT_EXPECT_EQ(test, access, LANDLOCK_ACCESS_FS_READ_DIR);
+
+ access = LANDLOCK_ACCESS_FS_WRITE_FILE;
+ KUNIT_EXPECT_EQ(test, 4,
+ get_denied_layer(&dom, &access, &layer_masks,
+ sizeof(layer_masks)));
+ KUNIT_EXPECT_EQ(test, access, 0);
+}
+
+#endif /* CONFIG_SECURITY_LANDLOCK_KUNIT_TEST */
+
static bool is_valid_request(const struct landlock_request *const request)
{
- if (WARN_ON_ONCE(!request->layer_plus_one))
+ if (WARN_ON_ONCE(!(!!request->layer_plus_one ^ !!request->access)))
+ return false;
+
+ if (request->access) {
+ if (WARN_ON_ONCE(!request->layer_masks))
+ return false;
+ } else {
+ if (WARN_ON_ONCE(request->layer_masks))
+ return false;
+ }
+
+ if (WARN_ON_ONCE(!!request->layer_masks ^ !!request->layer_masks_size))
return false;
return true;
@@ -140,6 +284,7 @@ void landlock_log_denial(const struct landlock_ruleset *const domain,
{
struct audit_buffer *ab;
struct landlock_hierarchy *youngest_denied;
+ access_mask_t missing;
if (WARN_ON_ONCE(!domain || !domain->hierarchy || !request))
return;
@@ -155,9 +300,24 @@ void landlock_log_denial(const struct landlock_ruleset *const domain,
if (!ab)
return;
- youngest_denied = get_hierarchy(domain, request->layer_plus_one - 1);
+ missing = request->access;
+ if (missing) {
+ size_t youngest_layer;
+
+ /* Gets the nearest domain that denies the request. */
+ if (request->layer_masks) {
+ youngest_layer = get_denied_layer(
+ domain, &missing, request->layer_masks,
+ request->layer_masks_size);
+ }
+ youngest_denied = get_hierarchy(domain, youngest_layer);
+ } else {
+ youngest_denied =
+ get_hierarchy(domain, request->layer_plus_one - 1);
+ }
+
audit_log_format(ab, "domain=%llu blockers=", youngest_denied->id);
- log_blockers(ab, request->type);
+ log_blockers(ab, request->type, missing);
audit_log_lsm_data(ab, &request->audit);
audit_log_end(ab);
@@ -204,6 +364,7 @@ void landlock_log_drop_domain(const struct landlock_ruleset *const domain)
static struct kunit_case test_cases[] = {
/* clang-format off */
KUNIT_CASE(test_get_hierarchy),
+ KUNIT_CASE(test_get_denied_layer),
{}
/* clang-format on */
};
diff --git a/security/landlock/audit.h b/security/landlock/audit.h
index 6f5ad04b83c2..25fc8333cddc 100644
--- a/security/landlock/audit.h
+++ b/security/landlock/audit.h
@@ -11,11 +11,13 @@
#include <linux/audit.h>
#include <linux/lsm_audit.h>
+#include "access.h"
#include "ruleset.h"
enum landlock_request_type {
LANDLOCK_REQUEST_PTRACE = 1,
LANDLOCK_REQUEST_FS_CHANGE_LAYOUT,
+ LANDLOCK_REQUEST_FS_ACCESS,
};
/*
@@ -33,6 +35,13 @@ struct landlock_request {
* extra one is useful to detect uninitialized field.
*/
size_t layer_plus_one;
+
+ /* Required field for configurable access control. */
+ access_mask_t access;
+
+ /* Required fields for requests with layer masks. */
+ const layer_mask_t (*layer_masks)[];
+ size_t layer_masks_size;
};
#ifdef CONFIG_AUDIT
diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index a099167d2347..7f69bed9e095 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -730,6 +730,7 @@ static void test_is_eacces_with_write(struct kunit *const test)
* those identified by @access_request_parent1). This matrix can
* initially refer to domain layer masks and, when the accesses for the
* destination and source are the same, to requested layer masks.
+ * @log_request_parent1: Audit request to fill if the related access is denied.
* @dentry_child1: Dentry to the initial child of the parent1 path. This
* pointer must be NULL for non-refer actions (i.e. not link nor rename).
* @access_request_parent2: Similar to @access_request_parent1 but for a
@@ -738,6 +739,7 @@ static void test_is_eacces_with_write(struct kunit *const test)
* the source. Must be set to 0 when using a simple path request.
* @layer_masks_parent2: Similar to @layer_masks_parent1 but for a refer
* action. This must be NULL otherwise.
+ * @log_request_parent2: Audit request to fill if the related access is denied.
* @dentry_child2: Dentry to the initial child of the parent2 path. This
* pointer is only set for RENAME_EXCHANGE actions and must be NULL
* otherwise.
@@ -757,10 +759,12 @@ static bool is_access_to_paths_allowed(
const struct path *const path,
const access_mask_t access_request_parent1,
layer_mask_t (*const layer_masks_parent1)[LANDLOCK_NUM_ACCESS_FS],
- const struct dentry *const dentry_child1,
+ struct landlock_request *const log_request_parent1,
+ struct dentry *const dentry_child1,
const access_mask_t access_request_parent2,
layer_mask_t (*const layer_masks_parent2)[LANDLOCK_NUM_ACCESS_FS],
- const struct dentry *const dentry_child2)
+ struct landlock_request *const log_request_parent2,
+ struct dentry *const dentry_child2)
{
bool allowed_parent1 = false, allowed_parent2 = false, is_dom_check,
child1_is_directory = true, child2_is_directory = true;
@@ -907,6 +911,24 @@ static bool is_access_to_paths_allowed(
}
path_put(&walker_path);
+ if (!allowed_parent1 && log_request_parent1) {
+ log_request_parent1->type = LANDLOCK_REQUEST_FS_ACCESS,
+ log_request_parent1->audit.type = LSM_AUDIT_DATA_PATH,
+ log_request_parent1->audit.u.path = *path;
+ log_request_parent1->access = access_request_parent1;
+ log_request_parent1->layer_masks = layer_masks_parent1;
+ log_request_parent1->layer_masks_size =
+ ARRAY_SIZE(*layer_masks_parent1);
+ }
+ if (!allowed_parent2 && log_request_parent2) {
+ log_request_parent2->type = LANDLOCK_REQUEST_FS_ACCESS,
+ log_request_parent2->audit.type = LSM_AUDIT_DATA_PATH,
+ log_request_parent2->audit.u.path = *path;
+ log_request_parent2->access = access_request_parent2;
+ log_request_parent2->layer_masks = layer_masks_parent2;
+ log_request_parent2->layer_masks_size =
+ ARRAY_SIZE(*layer_masks_parent2);
+ }
return allowed_parent1 && allowed_parent2;
}
@@ -915,6 +937,7 @@ static int current_check_access_path(const struct path *const path,
{
const struct landlock_ruleset *const dom = get_current_fs_domain();
layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_FS] = {};
+ struct landlock_request request = {};
if (!dom)
return 0;
@@ -922,9 +945,10 @@ static int current_check_access_path(const struct path *const path,
access_request = landlock_init_layer_masks(
dom, access_request, &layer_masks, LANDLOCK_KEY_INODE);
if (is_access_to_paths_allowed(dom, path, access_request, &layer_masks,
- NULL, 0, NULL, NULL))
+ &request, NULL, 0, NULL, NULL, NULL))
return 0;
+ landlock_log_denial(dom, &request);
return -EACCES;
}
@@ -1093,6 +1117,7 @@ static int current_check_refer_path(struct dentry *const old_dentry,
struct dentry *old_parent;
layer_mask_t layer_masks_parent1[LANDLOCK_NUM_ACCESS_FS] = {},
layer_masks_parent2[LANDLOCK_NUM_ACCESS_FS] = {};
+ struct landlock_request request1 = {}, request2 = {};
if (!dom)
return 0;
@@ -1124,10 +1149,13 @@ static int current_check_refer_path(struct dentry *const old_dentry,
access_request_parent1 = landlock_init_layer_masks(
dom, access_request_parent1 | access_request_parent2,
&layer_masks_parent1, LANDLOCK_KEY_INODE);
- if (is_access_to_paths_allowed(
- dom, new_dir, access_request_parent1,
- &layer_masks_parent1, NULL, 0, NULL, NULL))
+ if (is_access_to_paths_allowed(dom, new_dir,
+ access_request_parent1,
+ &layer_masks_parent1, &request1,
+ NULL, 0, NULL, NULL, NULL))
return 0;
+
+ landlock_log_denial(dom, &request1);
return -EACCES;
}
@@ -1162,12 +1190,22 @@ static int current_check_refer_path(struct dentry *const old_dentry,
* parent access rights. This will be useful to compare with the
* destination parent access rights.
*/
- if (is_access_to_paths_allowed(
- dom, &mnt_dir, access_request_parent1, &layer_masks_parent1,
- old_dentry, access_request_parent2, &layer_masks_parent2,
- exchange ? new_dentry : NULL))
+ if (is_access_to_paths_allowed(dom, &mnt_dir, access_request_parent1,
+ &layer_masks_parent1, &request1,
+ old_dentry, access_request_parent2,
+ &layer_masks_parent2, &request2,
+ exchange ? new_dentry : NULL))
return 0;
+ if (request1.access) {
+ request1.audit.u.path.dentry = old_parent;
+ landlock_log_denial(dom, &request1);
+ }
+ if (request2.access) {
+ request2.audit.u.path.dentry = new_dir->dentry;
+ landlock_log_denial(dom, &request2);
+ }
+
/*
* This prioritizes EACCES over EXDEV for all actions, including
* renames with RENAME_EXCHANGE.
@@ -1546,6 +1584,7 @@ static int hook_file_open(struct file *const file)
optional_access;
const struct landlock_ruleset *const dom = landlock_match_ruleset(
landlock_cred(file->f_cred)->domain, any_fs);
+ struct landlock_request request = {};
if (!dom)
return 0;
@@ -1571,7 +1610,7 @@ static int hook_file_open(struct file *const file)
dom, &file->f_path,
landlock_init_layer_masks(dom, full_access_request,
&layer_masks, LANDLOCK_KEY_INODE),
- &layer_masks, NULL, 0, NULL, NULL)) {
+ &layer_masks, &request, NULL, 0, NULL, NULL, NULL)) {
allowed_access = full_access_request;
} else {
unsigned long access_bit;
@@ -1601,6 +1640,9 @@ static int hook_file_open(struct file *const file)
if ((open_access_request & allowed_access) == open_access_request)
return 0;
+ /* Sets access to reflect the actual request. */
+ request.access = open_access_request;
+ landlock_log_denial(dom, &request);
return -EACCES;
}
--
2.47.0
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