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namespace-util: introduce userns_enter_and_pin() helper

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which generalizes forking a process into userns and freeze()

Addresses https://github.com/systemd/systemd/pull/35833/files#r1905508153
This commit is contained in:
Mike Yuan
2025-01-11 15:53:14 +01:00
parent c7704ecd04
commit 8c2c8235a6
3 changed files with 22 additions and 45 deletions
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src/basic/uid-range.c
+2 -41
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@@ -9,6 +9,7 @@
#include "fd-util.h"
#include "format-util.h"
#include "macro.h"
#include "namespace-util.h"
#include "path-util.h"
#include "process-util.h"
#include "sort-util.h"
@@ -264,10 +265,7 @@ int uid_range_load_userns(const char *path, UIDRangeUsernsMode mode, UIDRange **
}
int uid_range_load_userns_by_fd(int userns_fd, UIDRangeUsernsMode mode, UIDRange **ret) {
_cleanup_(close_pairp) int pfd[2] = EBADF_PAIR;
_cleanup_(sigkill_waitp) pid_t pid = 0;
ssize_t n;
char x;
int r;
assert(userns_fd >= 0);
@@ -275,46 +273,9 @@ int uid_range_load_userns_by_fd(int userns_fd, UIDRangeUsernsMode mode, UIDRange
assert(mode < _UID_RANGE_USERNS_MODE_MAX);
assert(ret);
if (pipe2(pfd, O_CLOEXEC) < 0)
return -errno;
r = safe_fork_full(
"(sd-mkuserns)",
/* stdio_fds= */ NULL,
(int[]) { pfd[1], userns_fd }, 2,
FORK_CLOSE_ALL_FDS|FORK_DEATHSIG_SIGKILL,
&pid);
r = userns_enter_and_pin(userns_fd, &pid);
if (r < 0)
return r;
if (r == 0) {
/* Child. */
if (setns(userns_fd, CLONE_NEWUSER) < 0) {
log_debug_errno(errno, "Failed to join userns: %m");
_exit(EXIT_FAILURE);
}
userns_fd = safe_close(userns_fd);
n = write(pfd[1], &(const char) { 'x' }, 1);
if (n < 0) {
log_debug_errno(errno, "Failed to write to fifo: %m");
_exit(EXIT_FAILURE);
}
assert(n == 1);
freeze();
}
pfd[1] = safe_close(pfd[1]);
n = read(pfd[0], &x, 1);
if (n < 0)
return -errno;
if (n == 0)
return -EPROTO;
assert(n == 1);
assert(x == 'x');
const char *p = procfs_file_alloca(
pid,