From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 24F0918D658; Mon, 23 Feb 2026 13:20:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771852821; cv=none; b=si+GKZlx8wsuO20aqCV4ibZ/cWOySmz+6xA2LJeUTPEnWH0yVzF/I3HGqTnbL2Qk51nAfRU7Z+nhiaSHi44uYnFXVc0TKbQy8ATK9IG6wfv9KDfN2FYXDUbvmODVE9eFGMebXUZsQgPeYM1nTlMn6Nhy30bTTGpv9VZwcW8zr7I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771852821; c=relaxed/simple; bh=ZxJIMdlct5l9zBlEujtxSo3Sysm2g8soeik3PzMFxM0=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=upvXIw5RUFu7Fn0w+YiUl+5GzTH8voKEfQOWa/oWoR58VvjmHNX+4b3fisiHWluIqT+D48CdLCCHBpeKP5RMExl9+SgNXfBZXSfcrC7Jm86M5wetXC7v3Sg+uBFAqSPSTQQHeE5hE9vPJedKD83ryQwAhoiC3CIBCZynCpjLMI4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=An+WTrsq; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="An+WTrsq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CBF70C19424; Mon, 23 Feb 2026 13:20:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771852820; bh=ZxJIMdlct5l9zBlEujtxSo3Sysm2g8soeik3PzMFxM0=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=An+WTrsqWyb+tpcRCwRd8YbfPY3xvbwa96UmrAJkhmLyt4KoA7G/32AsMDEodrn9c V1NSjQE9LI3roWPRnzu939M18D0daXjsQMDv2OoUUanPz+TZmCNFzwWC+UZ6j5P5NB 71W1xvexBiV5TyxIfPggrJZ51sl/Ql4iNcG4DSmGhlawlSCH+XmvaxHdnEr446HiUN t2G022llZh3KLnctdYeJD3T71CgaW2RrSyCCG52zri5UAfjT6EJhj/Mb6fJR9rXdLv LDToT1OQqcuUlOSQ3tUDRDMT36zml74ZvaeIUm/eVpx/lqVkptwCxwW3s9rUp46vfI j3ySGEuWu4ZVg== From: Christian Brauner Date: Mon, 23 Feb 2026 14:20:09 +0100 Subject: [PATCH RFC v3 2/2] selftests/pidfd: add inode ownership and permission tests Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260223-work-pidfs-inode-owner-v3-2-490855c59999@kernel.org> References: <20260223-work-pidfs-inode-owner-v3-0-490855c59999@kernel.org> In-Reply-To: <20260223-work-pidfs-inode-owner-v3-0-490855c59999@kernel.org> To: linux-fsdevel@vger.kernel.org, Jann Horn Cc: Kees Cook , Andy Lutomirski , Alexander Viro , Jan Kara , linux-kernel@vger.kernel.org, Christian Brauner X-Mailer: b4 0.15-dev-47773 X-Developer-Signature: v=1; a=openpgp-sha256; l=9030; i=brauner@kernel.org; h=from:subject:message-id; bh=ZxJIMdlct5l9zBlEujtxSo3Sysm2g8soeik3PzMFxM0=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMWTOCeErviKnxqMjcKk6yFqG4/mhXNn2muPz7r24c4PP7 3yiXI52RykLgxgXg6yYIotDu0m43HKeis1GmRowc1iZQIYwcHEKwESWpjEy7BXheuL3LnbV7QNd 1tK1XkldpXmlrnnRl25Y1xkdcvnyiJFhtlvVzyMLilfWqmxafFwnW3KvX8Xhlo1Mtcv12x/c3+L JDAA= X-Developer-Key: i=brauner@kernel.org; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 Test the pidfs inode ownership reporting (via fstat) and the permission model (via user.* xattr operations that trigger pidfs_permission()): Ownership tests: - owner_self: own pidfd reports caller's euid/egid - owner_child: child pidfd reports correct ownership - owner_child_changed_euid: ownership tracks live credential changes - owner_exited_child: ownership persists after exit and reap - owner_exited_child_changed_euid: exit_cred preserves changed credentials Permission tests: - permission_same_user: same-user xattr access succeeds (EOPNOTSUPP) - permission_different_user_denied: cross-user access denied (EPERM) - permission_kthread: kernel thread access always denied (EPERM) The user.* xattr namespace is used to exercise pidfs_permission() from userspace: xattr_permission() calls inode_permission() for user.* on S_IFREG inodes, so fgetxattr() returns EOPNOTSUPP when permission is granted (no handler) and EPERM when denied. Tests requiring root skip gracefully via SKIP(). Signed-off-by: Christian Brauner --- tools/testing/selftests/pidfd/.gitignore | 1 + tools/testing/selftests/pidfd/Makefile | 2 +- .../selftests/pidfd/pidfd_inode_owner_test.c | 289 +++++++++++++++++++++ 3 files changed, 291 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/pidfd/.gitignore b/tools/testing/selftests/pidfd/.gitignore index 144e7ff65d6a..1981d39fe3dc 100644 --- a/tools/testing/selftests/pidfd/.gitignore +++ b/tools/testing/selftests/pidfd/.gitignore @@ -12,3 +12,4 @@ pidfd_info_test pidfd_exec_helper pidfd_xattr_test pidfd_setattr_test +pidfd_inode_owner_test diff --git a/tools/testing/selftests/pidfd/Makefile b/tools/testing/selftests/pidfd/Makefile index 764a8f9ecefa..904c9fd595c1 100644 --- a/tools/testing/selftests/pidfd/Makefile +++ b/tools/testing/selftests/pidfd/Makefile @@ -4,7 +4,7 @@ CFLAGS += -g $(KHDR_INCLUDES) $(TOOLS_INCLUDES) -pthread -Wall TEST_GEN_PROGS := pidfd_test pidfd_fdinfo_test pidfd_open_test \ pidfd_poll_test pidfd_wait pidfd_getfd_test pidfd_setns_test \ pidfd_file_handle_test pidfd_bind_mount pidfd_info_test \ - pidfd_xattr_test pidfd_setattr_test + pidfd_xattr_test pidfd_setattr_test pidfd_inode_owner_test TEST_GEN_PROGS_EXTENDED := pidfd_exec_helper diff --git a/tools/testing/selftests/pidfd/pidfd_inode_owner_test.c b/tools/testing/selftests/pidfd/pidfd_inode_owner_test.c new file mode 100644 index 000000000000..58666b87638b --- /dev/null +++ b/tools/testing/selftests/pidfd/pidfd_inode_owner_test.c @@ -0,0 +1,289 @@ +// SPDX-License-Identifier: GPL-2.0 + +#define _GNU_SOURCE +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include "pidfd.h" +#include "kselftest_harness.h" + +FIXTURE(pidfs_inode_owner) +{ + pid_t child_pid; + int child_pidfd; +}; + +FIXTURE_SETUP(pidfs_inode_owner) +{ + int pipe_fds[2]; + char buf; + + self->child_pid = -1; + self->child_pidfd = -1; + + ASSERT_EQ(pipe(pipe_fds), 0); + + self->child_pid = create_child(&self->child_pidfd, 0); + ASSERT_GE(self->child_pid, 0); + + if (self->child_pid == 0) { + close(pipe_fds[0]); + write_nointr(pipe_fds[1], "c", 1); + close(pipe_fds[1]); + pause(); + _exit(EXIT_SUCCESS); + } + + close(pipe_fds[1]); + ASSERT_EQ(read_nointr(pipe_fds[0], &buf, 1), 1); + close(pipe_fds[0]); +} + +FIXTURE_TEARDOWN(pidfs_inode_owner) +{ + if (self->child_pid > 0) { + kill(self->child_pid, SIGKILL); + sys_waitid(P_PID, self->child_pid, NULL, WEXITED); + } + if (self->child_pidfd >= 0) + close(self->child_pidfd); +} + +/* Own pidfd reports correct ownership. */ +TEST_F(pidfs_inode_owner, owner_self) +{ + int pidfd; + struct stat st; + + pidfd = sys_pidfd_open(getpid(), 0); + ASSERT_GE(pidfd, 0); + + ASSERT_EQ(fstat(pidfd, &st), 0); + EXPECT_EQ(st.st_uid, geteuid()); + EXPECT_EQ(st.st_gid, getegid()); + + close(pidfd); +} + +/* Child pidfd reports correct ownership. */ +TEST_F(pidfs_inode_owner, owner_child) +{ + struct stat st; + + ASSERT_EQ(fstat(self->child_pidfd, &st), 0); + EXPECT_EQ(st.st_uid, geteuid()); + EXPECT_EQ(st.st_gid, getegid()); +} + +/* Ownership tracks credential changes in a live task. */ +TEST_F(pidfs_inode_owner, owner_child_changed_euid) +{ + pid_t pid; + int pidfd, pipe_fds[2]; + struct stat st; + char buf; + + if (getuid() != 0) + SKIP(return, "Test requires root"); + + ASSERT_EQ(pipe(pipe_fds), 0); + + pid = create_child(&pidfd, 0); + ASSERT_GE(pid, 0); + + if (pid == 0) { + close(pipe_fds[0]); + if (setresgid(65534, 65534, 65534)) + _exit(PIDFD_ERROR); + if (setresuid(65534, 65534, 65534)) + _exit(PIDFD_ERROR); + write_nointr(pipe_fds[1], "c", 1); + close(pipe_fds[1]); + pause(); + _exit(EXIT_SUCCESS); + } + + close(pipe_fds[1]); + ASSERT_EQ(read_nointr(pipe_fds[0], &buf, 1), 1); + close(pipe_fds[0]); + + ASSERT_EQ(fstat(pidfd, &st), 0); + EXPECT_EQ(st.st_uid, (uid_t)65534); + EXPECT_EQ(st.st_gid, (gid_t)65534); + + kill(pid, SIGKILL); + sys_waitid(P_PID, pid, NULL, WEXITED); + close(pidfd); +} + +/* Ownership persists after the child exits and is reaped. */ +TEST_F(pidfs_inode_owner, owner_exited_child) +{ + pid_t pid; + int pidfd; + struct stat st; + + pid = create_child(&pidfd, 0); + ASSERT_GE(pid, 0); + + if (pid == 0) + _exit(EXIT_SUCCESS); + + ASSERT_EQ(sys_waitid(P_PID, pid, NULL, WEXITED), 0); + + ASSERT_EQ(fstat(pidfd, &st), 0); + EXPECT_EQ(st.st_uid, geteuid()); + EXPECT_EQ(st.st_gid, getegid()); + + close(pidfd); +} + +/* Exit credentials preserve changed credentials. */ +TEST_F(pidfs_inode_owner, owner_exited_child_changed_euid) +{ + pid_t pid; + int pidfd; + struct stat st; + + if (getuid() != 0) + SKIP(return, "Test requires root"); + + pid = create_child(&pidfd, 0); + ASSERT_GE(pid, 0); + + if (pid == 0) { + if (setresgid(65534, 65534, 65534)) + _exit(PIDFD_ERROR); + if (setresuid(65534, 65534, 65534)) + _exit(PIDFD_ERROR); + _exit(EXIT_SUCCESS); + } + + ASSERT_EQ(sys_waitid(P_PID, pid, NULL, WEXITED), 0); + + ASSERT_EQ(fstat(pidfd, &st), 0); + EXPECT_EQ(st.st_uid, (uid_t)65534); + EXPECT_EQ(st.st_gid, (gid_t)65534); + + close(pidfd); +} + +/* Same-user cross-process permission check succeeds. */ +TEST_F(pidfs_inode_owner, permission_same_user) +{ + pid_t pid; + int pidfd; + pid_t parent_pid = getpid(); + + pid = create_child(&pidfd, 0); + ASSERT_GE(pid, 0); + + if (pid == 0) { + int fd; + char buf; + + fd = sys_pidfd_open(parent_pid, 0); + if (fd < 0) + _exit(PIDFD_ERROR); + + /* + * user.* xattr access triggers pidfs_permission(). + * Same user passes may_signal_creds() and + * generic_permission(), so we get EOPNOTSUPP + * (no user.* xattr handler) instead of EPERM. + */ + if (fgetxattr(fd, "user.test", &buf, sizeof(buf)) < 0 && + errno == EOPNOTSUPP) { + close(fd); + _exit(PIDFD_PASS); + } + + close(fd); + _exit(PIDFD_FAIL); + } + + ASSERT_EQ(wait_for_pid(pid), PIDFD_PASS); + close(pidfd); +} + +/* Cross-user access is denied without signal permission. */ +TEST_F(pidfs_inode_owner, permission_different_user_denied) +{ + pid_t pid; + int pidfd; + + if (getuid() != 0) + SKIP(return, "Test requires root"); + + pid = create_child(&pidfd, 0); + ASSERT_GE(pid, 0); + + if (pid == 0) { + int fd; + char buf; + + /* Drop to uid/gid 65534 and lose all capabilities. */ + if (setresgid(65534, 65534, 65534)) + _exit(PIDFD_ERROR); + if (setresuid(65534, 65534, 65534)) + _exit(PIDFD_ERROR); + + /* Open pidfd for init (uid 0). */ + fd = sys_pidfd_open(1, 0); + if (fd < 0) + _exit(PIDFD_ERROR); + + /* + * uid 65534 cannot signal uid 0 (no CAP_KILL), + * so pidfs_permission() denies access. + */ + if (fgetxattr(fd, "user.test", &buf, sizeof(buf)) < 0 && + errno == EPERM) { + close(fd); + _exit(PIDFD_PASS); + } + + close(fd); + _exit(PIDFD_FAIL); + } + + ASSERT_EQ(wait_for_pid(pid), PIDFD_PASS); + close(pidfd); +} + +/* Kernel thread access is always denied. */ +TEST_F(pidfs_inode_owner, permission_kthread) +{ + int pidfd; + struct stat st; + char buf; + + /* pid 2 is kthreadd. */ + pidfd = sys_pidfd_open(2, 0); + ASSERT_GE(pidfd, 0); + + /* pidfs_permission() returns EPERM for kernel threads. */ + ASSERT_LT(fgetxattr(pidfd, "user.test", &buf, sizeof(buf)), 0); + EXPECT_EQ(errno, EPERM); + + /* fstat bypasses permission and reports root ownership. */ + ASSERT_EQ(fstat(pidfd, &st), 0); + EXPECT_EQ(st.st_uid, (uid_t)0); + EXPECT_EQ(st.st_gid, (gid_t)0); + + close(pidfd); +} + +TEST_HARNESS_MAIN -- 2.47.3