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From: "Mickaël Salaün" <mic@digikod.net>
To: James Morris <jmorris@namei.org>, "Serge E . Hallyn" <serge@hallyn.com>
Cc: "Mickaël Salaün" <mic@digikod.net>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Jann Horn" <jannh@google.com>,
	"John Johansen" <john.johansen@canonical.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Konstantin Meskhidze" <konstantin.meskhidze@huawei.com>,
	"Paul Moore" <paul@paul-moore.com>,
	"Shuah Khan" <shuah@kernel.org>,
	"Tetsuo Handa" <penguin-kernel@I-love.SAKURA.ne.jp>,
	linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-security-module@vger.kernel.org
Subject: [PATCH v3 09/12] samples/landlock: Add support for file reparenting
Date: Fri,  6 May 2022 18:10:59 +0200	[thread overview]
Message-ID: <20220506161102.525323-10-mic@digikod.net> (raw)
In-Reply-To: <20220506161102.525323-1-mic@digikod.net>

Add LANDLOCK_ACCESS_FS_REFER to the "roughly write" access rights and
leverage the Landlock ABI version to only try to enforce it if it is
supported by the running kernel.

Reviewed-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20220506161102.525323-10-mic@digikod.net
---

Changes since v2:
* Format with clang-format and rebase.

Changes since v1:
* Add Reviewed-by: Paul Moore.
---
 samples/landlock/sandboxer.c | 40 ++++++++++++++++++++++++------------
 1 file changed, 27 insertions(+), 13 deletions(-)

diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
index c089e9cdaf32..3e404e51ec64 100644
--- a/samples/landlock/sandboxer.c
+++ b/samples/landlock/sandboxer.c
@@ -159,7 +159,11 @@ static int populate_ruleset(const char *const env_var, const int ruleset_fd,
 	LANDLOCK_ACCESS_FS_MAKE_SOCK | \
 	LANDLOCK_ACCESS_FS_MAKE_FIFO | \
 	LANDLOCK_ACCESS_FS_MAKE_BLOCK | \
-	LANDLOCK_ACCESS_FS_MAKE_SYM)
+	LANDLOCK_ACCESS_FS_MAKE_SYM | \
+	LANDLOCK_ACCESS_FS_REFER)
+
+#define ACCESS_ABI_2 ( \
+	LANDLOCK_ACCESS_FS_REFER)
 
 /* clang-format on */
 
@@ -167,10 +171,11 @@ int main(const int argc, char *const argv[], char *const *const envp)
 {
 	const char *cmd_path;
 	char *const *cmd_argv;
-	int ruleset_fd;
+	int ruleset_fd, abi;
+	__u64 access_fs_ro = ACCESS_FS_ROUGHLY_READ,
+	      access_fs_rw = ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE;
 	struct landlock_ruleset_attr ruleset_attr = {
-		.handled_access_fs = ACCESS_FS_ROUGHLY_READ |
-				     ACCESS_FS_ROUGHLY_WRITE,
+		.handled_access_fs = access_fs_rw,
 	};
 
 	if (argc < 2) {
@@ -196,12 +201,11 @@ int main(const int argc, char *const argv[], char *const *const envp)
 		return 1;
 	}
 
-	ruleset_fd =
-		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
-	if (ruleset_fd < 0) {
+	abi = landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION);
+	if (abi < 0) {
 		const int err = errno;
 
-		perror("Failed to create a ruleset");
+		perror("Failed to check Landlock compatibility");
 		switch (err) {
 		case ENOSYS:
 			fprintf(stderr,
@@ -221,13 +225,23 @@ int main(const int argc, char *const argv[], char *const *const envp)
 		}
 		return 1;
 	}
-	if (populate_ruleset(ENV_FS_RO_NAME, ruleset_fd,
-			     ACCESS_FS_ROUGHLY_READ)) {
+	/* Best-effort security. */
+	if (abi < 2) {
+		ruleset_attr.handled_access_fs &= ~ACCESS_ABI_2;
+		access_fs_ro &= ~ACCESS_ABI_2;
+		access_fs_rw &= ~ACCESS_ABI_2;
+	}
+
+	ruleset_fd =
+		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
+	if (ruleset_fd < 0) {
+		perror("Failed to create a ruleset");
+		return 1;
+	}
+	if (populate_ruleset(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro)) {
 		goto err_close_ruleset;
 	}
-	if (populate_ruleset(ENV_FS_RW_NAME, ruleset_fd,
-			     ACCESS_FS_ROUGHLY_READ |
-				     ACCESS_FS_ROUGHLY_WRITE)) {
+	if (populate_ruleset(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) {
 		goto err_close_ruleset;
 	}
 	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
-- 
2.35.1


  parent reply	other threads:[~2022-05-06 16:11 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-06 16:10 [PATCH v3 00/12] Landlock: file linking and renaming support Mickaël Salaün
2022-05-06 16:10 ` [PATCH v3 01/12] landlock: Define access_mask_t to enforce a consistent access mask size Mickaël Salaün
2022-05-06 16:10 ` [PATCH v3 02/12] landlock: Reduce the maximum number of layers to 16 Mickaël Salaün
2022-05-06 16:10 ` [PATCH v3 03/12] landlock: Create find_rule() from unmask_layers() Mickaël Salaün
2022-05-06 16:10 ` [PATCH v3 04/12] landlock: Fix same-layer rule unions Mickaël Salaün
2022-05-06 16:10 ` [PATCH v3 05/12] landlock: Move filesystem helpers and add a new one Mickaël Salaün
2022-05-06 16:10 ` [PATCH v3 06/12] LSM: Remove double path_rename hook calls for RENAME_EXCHANGE Mickaël Salaün
2022-05-06 16:10 ` [PATCH v3 07/12] landlock: Add support for file reparenting with LANDLOCK_ACCESS_FS_REFER Mickaël Salaün
2022-05-06 16:10 ` [PATCH v3 08/12] selftests/landlock: Add 11 new test suites dedicated to file reparenting Mickaël Salaün
2022-05-06 16:10 ` Mickaël Salaün [this message]
2022-05-06 16:11 ` [PATCH v3 10/12] landlock: Document LANDLOCK_ACCESS_FS_REFER and ABI versioning Mickaël Salaün
2022-05-06 16:11 ` [PATCH v3 11/12] landlock: Document good practices about filesystem policies Mickaël Salaün
2022-05-06 16:11 ` [PATCH v3 12/12] landlock: Add design choices documentation for filesystem access rights Mickaël Salaün
2022-05-06 16:31 ` [PATCH v3 00/12] Landlock: file linking and renaming support Mickaël Salaün

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