From 6431c34b8a8487fb50c9cb850bd7d3bf81ad9e2a Mon Sep 17 00:00:00 2001 From: Lennart Poettering Date: Mon, 10 Mar 2025 11:24:59 +0100 Subject: [PATCH] namespace-util: make "setgroups" users property writable via userns_acquire() Unprivileged namespaces are only allowed if the "setgroups" file is set to "deny" for processes. And we need to write it before writing the gidmap. Hence add a parameter for that. Then, also patch all current users to actually enable this. The usecase generally don't need it (because they don't care about unprivileged userns), but it doesn't hurt to enable the concept anyway in all current users (none of them actually runs complex userspace in them, but they mostly use userns_acquire() for idmapped mounts and similar). Let's anyway make this option explicit in the function call, to indicate that the concept exists and is applied. --- src/basic/namespace-util.c | 13 ++++++++++--- src/basic/namespace-util.h | 2 +- src/core/namespace.c | 2 +- src/home/homework-mount.c | 2 +- src/mountfsd/mountwork.c | 2 +- src/nsresourced/test-userns-restrict.c | 2 +- src/shared/mount-util.c | 2 +- src/test/test-namespace.c | 2 +- 8 files changed, 17 insertions(+), 10 deletions(-) diff --git a/src/basic/namespace-util.c b/src/basic/namespace-util.c index 322cba4cf3..b24901c082 100644 --- a/src/basic/namespace-util.c +++ b/src/basic/namespace-util.c @@ -524,8 +524,8 @@ int userns_acquire_empty(void) { return pidref_namespace_open_by_type(&pid, NAMESPACE_USER); } -int userns_acquire(const char *uid_map, const char *gid_map) { - char path[STRLEN("/proc//uid_map") + DECIMAL_STR_MAX(pid_t) + 1]; +int userns_acquire(const char *uid_map, const char *gid_map, bool setgroups_deny) { + char path[STRLEN("/proc//setgroups") + DECIMAL_STR_MAX(pid_t) + 1]; _cleanup_(pidref_done_sigkill_wait) PidRef pid = PIDREF_NULL; int r; @@ -546,6 +546,13 @@ int userns_acquire(const char *uid_map, const char *gid_map) { if (r < 0) return log_debug_errno(r, "Failed to write UID map: %m"); + if (setgroups_deny) { + xsprintf(path, "/proc/" PID_FMT "/setgroups", pid.pid); + r = write_string_file(path, "deny", WRITE_STRING_FILE_DISABLE_BUFFER); + if (r < 0) + return log_debug_errno(r, "Failed to write setgroups file: %m"); + } + xsprintf(path, "/proc/" PID_FMT "/gid_map", pid.pid); r = write_string_file(path, gid_map, WRITE_STRING_FILE_DISABLE_BUFFER); if (r < 0) @@ -713,7 +720,7 @@ int is_idmapping_supported(const char *path) { if (r < 0) return r; - userns_fd = r = userns_acquire(uid_map, gid_map); + userns_fd = r = userns_acquire(uid_map, gid_map, /* setgroups_deny= */ true); if (ERRNO_IS_NEG_NOT_SUPPORTED(r) || ERRNO_IS_NEG_PRIVILEGE(r) || r == -EINVAL) return false; if (r == -ENOSPC) { diff --git a/src/basic/namespace-util.h b/src/basic/namespace-util.h index 3d40a515e7..74fd8a96d4 100644 --- a/src/basic/namespace-util.h +++ b/src/basic/namespace-util.h @@ -86,7 +86,7 @@ static inline bool userns_shift_range_valid(uid_t shift, uid_t range) { int parse_userns_uid_range(const char *s, uid_t *ret_uid_shift, uid_t *ret_uid_range); int userns_acquire_empty(void); -int userns_acquire(const char *uid_map, const char *gid_map); +int userns_acquire(const char *uid_map, const char *gid_map, bool setgroups_deny); int userns_enter_and_pin(int userns_fd, pid_t *ret_pid); int userns_get_base_uid(int userns_fd, uid_t *ret_uid, gid_t *ret_gid); diff --git a/src/core/namespace.c b/src/core/namespace.c index e801b6ea60..0943e0818f 100644 --- a/src/core/namespace.c +++ b/src/core/namespace.c @@ -1917,7 +1917,7 @@ static int apply_one_mount( return log_oom(); } - userns_fd = userns_acquire(uid_map, gid_map); + userns_fd = userns_acquire(uid_map, gid_map, /* setgroups_deny= */ true); if (userns_fd < 0) return log_error_errno(userns_fd, "Failed to allocate user namespace: %m"); diff --git a/src/home/homework-mount.c b/src/home/homework-mount.c index 085ba09e81..52115d86be 100644 --- a/src/home/homework-mount.c +++ b/src/home/homework-mount.c @@ -232,7 +232,7 @@ static int make_home_userns(uid_t stored_uid, uid_t exposed_uid) { log_debug("Creating userns with mapping:\n%s", text); - userns_fd = userns_acquire(text, text); /* same uid + gid mapping */ + userns_fd = userns_acquire(text, text, /* setgroups_deny= */ true); /* same uid + gid mapping */ if (userns_fd < 0) return log_error_errno(userns_fd, "Failed to allocate user namespace: %m"); diff --git a/src/mountfsd/mountwork.c b/src/mountfsd/mountwork.c index eaf72893aa..41c1d65391 100644 --- a/src/mountfsd/mountwork.c +++ b/src/mountfsd/mountwork.c @@ -860,7 +860,7 @@ static int vl_method_mount_directory( if (r < 0) return r; - _cleanup_close_ int idmap_userns_fd = userns_acquire(new_uid_map, new_uid_map); + _cleanup_close_ int idmap_userns_fd = userns_acquire(new_uid_map, new_uid_map, /* setgroups_deny= */ true); if (idmap_userns_fd < 0) return log_debug_errno(idmap_userns_fd, "Failed to acquire user namespace for id mapping: %m"); diff --git a/src/nsresourced/test-userns-restrict.c b/src/nsresourced/test-userns-restrict.c index d6df02428e..59ca1cabbb 100644 --- a/src/nsresourced/test-userns-restrict.c +++ b/src/nsresourced/test-userns-restrict.c @@ -78,7 +78,7 @@ static int run(int argc, char *argv[]) { host_tmpfs = make_tmpfs_fsmount(); assert_se(host_tmpfs >= 0); - userns_fd = userns_acquire("0 0 1", "0 0 1"); + userns_fd = userns_acquire("0 0 1", "0 0 1", /* setgroups_deny= */ true); if (userns_fd < 0) return log_error_errno(userns_fd, "Failed to make user namespace: %m"); diff --git a/src/shared/mount-util.c b/src/shared/mount-util.c index 97ff6d0764..d7471bc78d 100644 --- a/src/shared/mount-util.c +++ b/src/shared/mount-util.c @@ -1442,7 +1442,7 @@ int make_userns(uid_t uid_shift, } /* We always assign the same UID and GID ranges */ - userns_fd = userns_acquire(line, line); + userns_fd = userns_acquire(line, line, /* setgroups_deny= */ true); if (userns_fd < 0) return log_debug_errno(userns_fd, "Failed to acquire new userns: %m"); diff --git a/src/test/test-namespace.c b/src/test/test-namespace.c index cae65a14b1..52049efdb8 100644 --- a/src/test/test-namespace.c +++ b/src/test/test-namespace.c @@ -258,7 +258,7 @@ TEST(namespace_is_init) { TEST(userns_get_base_uid) { _cleanup_close_ int fd = -EBADF; - fd = userns_acquire("0 1 1", "0 2 1"); + fd = userns_acquire("0 1 1", "0 2 1", /* setgroups_deny= */ true); if (ERRNO_IS_NEG_NOT_SUPPORTED(fd)) return (void) log_tests_skipped("userns is not supported"); if (ERRNO_IS_NEG_PRIVILEGE(fd))