SymbX/systemd
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

fd-util: split out fallback logic for close_all_fds()

Browse Source 
No functional change. Just refactoring.

With this change, we can test each logic directly without seccomp
or hiding procfs.
This commit is contained in:
Yu Watanabe
2025-09-10 19:20:50 +09:00
parent e52a1acb81
commit 93d037dbd0
3 changed files with 96 additions and 153 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/basic/fd-util.c
+83 -79
View File
@@ -248,7 +248,7 @@ int get_max_fd(void) {
return (int) (m - 1);
}
static int close_all_fds_frugal(const int except[], size_t n_except) {
int close_all_fds_frugal(const int except[], size_t n_except) {
int max_fd, r = 0;
assert(except || n_except == 0);
@@ -282,6 +282,42 @@ static int close_all_fds_frugal(const int except[], size_t n_except) {
return r;
}
int close_all_fds_by_proc(const int except[], size_t n_except) {
_cleanup_closedir_ DIR *d = NULL;
int r = 0;
d = opendir("/proc/self/fd");
if (!d)
return close_all_fds_frugal(except, n_except); /* ultimate fallback if /proc/ is not available */
FOREACH_DIRENT(de, d, return -errno) {
int fd = -EBADF, q;
if (!IN_SET(de->d_type, DT_LNK, DT_UNKNOWN))
continue;
fd = parse_fd(de->d_name);
if (fd < 0)
/* Let's better ignore this, just in case */
continue;
if (fd < 3)
continue;
if (fd == dirfd(d))
continue;
if (fd_in_set(fd, except, n_except))
continue;
q = close_nointr(fd);
if (q != -EBADF) /* Valgrind has its own FD and doesn't want to have it closed */
RET_GATHER(r, q);
}
return r;
}
static bool have_close_range = true; /* Assume we live in the future */
static int close_all_fds_special_case(const int except[], size_t n_except) {
@@ -348,8 +384,7 @@ int close_all_fds_without_malloc(const int except[], size_t n_except) {
}
int close_all_fds(const int except[], size_t n_except) {
_cleanup_closedir_ DIR *d = NULL;
int r = 0;
int r;
assert(n_except == 0 || except);
@@ -359,104 +394,73 @@ int close_all_fds(const int except[], size_t n_except) {
if (r > 0) /* special case worked! */
return 0;
if (have_close_range) {
_cleanup_free_ int *sorted_malloc = NULL;
size_t n_sorted;
int *sorted;
if (!have_close_range)
return close_all_fds_by_proc(except, n_except);
/* In the best case we have close_range() to close all fds between a start and an end fd,
* which we can use on the "inverted" exception array, i.e. all intervals between all
* adjacent pairs from the sorted exception array. This changes loop complexity from O(n)
* where n is number of open fds to O(m⋅log(m)) where m is the number of fds to keep
* open. Given that we assume n ≫ m that's preferable to us. */
_cleanup_free_ int *sorted_malloc = NULL;
size_t n_sorted;
int *sorted;
assert(n_except < SIZE_MAX);
n_sorted = n_except + 1;
/* In the best case we have close_range() to close all fds between a start and an end fd, which we
* can use on the "inverted" exception array, i.e. all intervals between all adjacent pairs from the
* sorted exception array. This changes loop complexity from O(n) where n is number of open fds to
* O(m⋅log(m)) where m is the number of fds to keep open. Given that we assume n ≫ m that's
* preferable to us. */
if (n_sorted > 64) /* Use heap for large numbers of fds, stack otherwise */
sorted = sorted_malloc = new(int, n_sorted);
else
sorted = newa(int, n_sorted);
assert(n_except < SIZE_MAX);
n_sorted = n_except + 1;
if (sorted) {
memcpy(sorted, except, n_except * sizeof(int));
if (n_sorted > 64) /* Use heap for large numbers of fds, stack otherwise */
sorted = sorted_malloc = new(int, n_sorted);
else
sorted = newa(int, n_sorted);
/* Let's add fd 2 to the list of fds, to simplify the loop below, as this
* allows us to cover the head of the array the same way as the body */
sorted[n_sorted-1] = 2;
if (!sorted) /* Fallback on OOM. */
return close_all_fds_by_proc(except, n_except);
typesafe_qsort(sorted, n_sorted, cmp_int);
memcpy(sorted, except, n_except * sizeof(int));
for (size_t i = 0; i < n_sorted-1; i++) {
int start, end;
/* Let's add fd 2 to the list of fds, to simplify the loop below, as this
* allows us to cover the head of the array the same way as the body */
sorted[n_sorted-1] = 2;
start = MAX(sorted[i], 2); /* The first three fds shall always remain open */
end = MAX(sorted[i+1], 2);
typesafe_qsort(sorted, n_sorted, cmp_int);
assert(end >= start);
for (size_t i = 0; i < n_sorted-1; i++) {
int start, end;
if (end - start <= 1)
continue;
start = MAX(sorted[i], 2); /* The first three fds shall always remain open */
end = MAX(sorted[i+1], 2);
/* Close everything between the start and end fds (both of which shall stay open) */
if (close_range(start + 1, end - 1, 0) < 0) {
if (!ERRNO_IS_NOT_SUPPORTED(errno) && !ERRNO_IS_PRIVILEGE(errno))
return -errno;
assert(end >= start);
have_close_range = false;
break;
}
}
if (end - start <= 1)
continue;
if (have_close_range) {
/* The loop succeeded. Let's now close everything beyond the end */
/* Close everything between the start and end fds (both of which shall stay open) */
if (close_range(start + 1, end - 1, 0) < 0) {
if (!ERRNO_IS_NOT_SUPPORTED(errno) && !ERRNO_IS_PRIVILEGE(errno))
return -errno;
if (sorted[n_sorted-1] >= INT_MAX) /* Dont let the addition below overflow */
return 0;
if (close_range(sorted[n_sorted-1] + 1, INT_MAX, 0) >= 0)
return 0;
if (!ERRNO_IS_NOT_SUPPORTED(errno) && !ERRNO_IS_PRIVILEGE(errno))
return -errno;
have_close_range = false;
}
have_close_range = false;
return close_all_fds_by_proc(except, n_except);
}
/* Fallback on OOM or if close_range() is not supported */
}
d = opendir("/proc/self/fd");
if (!d)
return close_all_fds_frugal(except, n_except); /* ultimate fallback if /proc/ is not available */
/* The loop succeeded. Let's now close everything beyond the end */
FOREACH_DIRENT(de, d, return -errno) {
int fd = -EBADF, q;
if (sorted[n_sorted-1] >= INT_MAX) /* Dont let the addition below overflow */
return 0;
if (!IN_SET(de->d_type, DT_LNK, DT_UNKNOWN))
continue;
if (close_range(sorted[n_sorted-1] + 1, INT_MAX, 0) < 0) {
if (!ERRNO_IS_NOT_SUPPORTED(errno) && !ERRNO_IS_PRIVILEGE(errno))
return -errno;
fd = parse_fd(de->d_name);
if (fd < 0)
/* Let's better ignore this, just in case */
continue;
if (fd < 3)
continue;
if (fd == dirfd(d))
continue;
if (fd_in_set(fd, except, n_except))
continue;
q = close_nointr(fd);
if (q < 0 && q != -EBADF && r >= 0) /* Valgrind has its own FD and doesn't want to have it closed */
r = q;
have_close_range = false;
return close_all_fds_by_proc(except, n_except);
}
return r;
return 0;
}
int pack_fds(int fds[], size_t n_fds) {
src/basic/fd-util.h
+2
View File
@@ -112,6 +112,8 @@ int get_max_fd(void);
int close_all_fds(const int except[], size_t n_except);
int close_all_fds_without_malloc(const int except[], size_t n_except);
int close_all_fds_by_proc(const int except[], size_t n_except);
int close_all_fds_frugal(const int except[], size_t n_except);
int pack_fds(int fds[], size_t n);
src/test/test-fd-util.c
+11 -74
View File
@@ -260,7 +260,7 @@ static size_t validate_fds(
return c; /* Return number of fds >= 0 in the array */
}
static void test_close_all_fds_inner(void) {
static void test_close_all_fds_inner(int (*func)(const int except[], size_t n_except)) {
_cleanup_free_ int *fds = NULL, *keep = NULL;
size_t n_fds, n_keep;
int max_fd;
@@ -320,13 +320,13 @@ static void test_close_all_fds_inner(void) {
log_settle_target();
/* Close all but the ones to keep */
assert_se(close_all_fds(keep, n_keep) >= 0);
ASSERT_OK(func(keep, n_keep));
assert_se(validate_fds(false, fds, n_fds) == n_fds - n_keep);
assert_se(validate_fds(true, keep, n_keep) == n_keep);
/* Close everything else too! */
assert_se(close_all_fds(NULL, 0) >= 0);
ASSERT_OK(func(NULL, 0));
assert_se(validate_fds(false, fds, n_fds) == n_fds - n_keep);
assert_se(validate_fds(false, keep, n_keep) == n_keep);
@@ -335,95 +335,32 @@ static void test_close_all_fds_inner(void) {
log_open();
}
static int seccomp_prohibit_close_range(void) {
#if HAVE_SECCOMP && defined(__SNR_close_range)
_cleanup_(seccomp_releasep) scmp_filter_ctx seccomp = NULL;
int r;
r = seccomp_init_for_arch(&seccomp, SCMP_ARCH_NATIVE, SCMP_ACT_ALLOW);
if (r < 0)
return log_warning_errno(r, "Failed to acquire seccomp context, ignoring: %m");
r = seccomp_rule_add_exact(
seccomp,
SCMP_ACT_ERRNO(EPERM),
SCMP_SYS(close_range),
0);
if (r < 0)
return log_warning_errno(r, "Failed to add close_range() rule, ignoring: %m");
r = seccomp_load(seccomp);
if (r < 0)
return log_warning_errno(r, "Failed to apply close_range() restrictions, ignoring: %m");
return 0;
#else
return log_warning_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "Seccomp support or close_range() syscall definition not available.");
#endif
}
TEST(close_all_fds) {
int r;
/* Runs the test four times. Once as is. Once with close_range() syscall blocked via seccomp, once
* with /proc/ overmounted, and once with the combination of both. This should trigger all fallbacks
* in the close_range_all() function. */
r = safe_fork("(caf-plain)", FORK_CLOSE_ALL_FDS|FORK_DEATHSIG_SIGTERM|FORK_LOG|FORK_WAIT, NULL);
ASSERT_OK(r = safe_fork("(caf-plain)", FORK_CLOSE_ALL_FDS|FORK_DEATHSIG_SIGTERM|FORK_LOG|FORK_WAIT, NULL));
if (r == 0) {
test_close_all_fds_inner();
test_close_all_fds_inner(close_all_fds);
_exit(EXIT_SUCCESS);
}
assert_se(r >= 0);
if (geteuid() != 0)
return (void) log_tests_skipped("Lacking privileges for test with close_range() blocked and /proc/ overmounted");
r = safe_fork("(caf-noproc)", FORK_CLOSE_ALL_FDS|FORK_DEATHSIG_SIGTERM|FORK_LOG|FORK_WAIT|FORK_NEW_MOUNTNS|FORK_MOUNTNS_SLAVE, NULL);
ASSERT_OK(r = safe_fork("(caf-nomalloc)", FORK_CLOSE_ALL_FDS|FORK_DEATHSIG_SIGTERM|FORK_LOG|FORK_WAIT, NULL));
if (r == 0) {
r = mount_nofollow_verbose(LOG_WARNING, "tmpfs", "/proc", "tmpfs", 0, NULL);
if (r < 0)
log_notice("Overmounting /proc/ didn't work, skipping close_all_fds() with masked /proc/.");
else
test_close_all_fds_inner();
test_close_all_fds_inner(close_all_fds_without_malloc);
_exit(EXIT_SUCCESS);
}
if (ERRNO_IS_NEG_PRIVILEGE(r))
return (void) log_tests_skipped("Lacking privileges for test in namespace with /proc/ overmounted");
assert_se(r >= 0);
if (!is_seccomp_available())
return (void) log_tests_skipped("Seccomp not available");
r = safe_fork("(caf-seccomp)", FORK_CLOSE_ALL_FDS|FORK_DEATHSIG_SIGTERM|FORK_LOG|FORK_WAIT, NULL);
ASSERT_OK(r = safe_fork("(caf-proc)", FORK_CLOSE_ALL_FDS|FORK_DEATHSIG_SIGTERM|FORK_LOG|FORK_WAIT, NULL));
if (r == 0) {
r = seccomp_prohibit_close_range();
if (r < 0)
log_notice("Applying seccomp filter didn't work, skipping close_all_fds() test with masked close_range().");
else
test_close_all_fds_inner();
test_close_all_fds_inner(close_all_fds_by_proc);
_exit(EXIT_SUCCESS);
}
assert_se(r >= 0);
r = safe_fork("(caf-scnp)", FORK_CLOSE_ALL_FDS|FORK_DEATHSIG_SIGTERM|FORK_LOG|FORK_WAIT|FORK_NEW_MOUNTNS|FORK_MOUNTNS_SLAVE, NULL);
ASSERT_OK(r = safe_fork("(caf-frugal)", FORK_CLOSE_ALL_FDS|FORK_DEATHSIG_SIGTERM|FORK_LOG|FORK_WAIT, NULL));
if (r == 0) {
r = seccomp_prohibit_close_range();
if (r < 0)
log_notice("Applying seccomp filter didn't work, skipping close_all_fds() test with masked close_range().");
else {
r = mount_nofollow_verbose(LOG_WARNING, "tmpfs", "/proc", "tmpfs", 0, NULL);
if (r < 0)
log_notice("Overmounting /proc/ didn't work, skipping close_all_fds() with masked /proc/.");
else
test_close_all_fds_inner();
}
test_close_all_fds_inner();
test_close_all_fds_inner(close_all_fds_frugal);
_exit(EXIT_SUCCESS);
}
assert_se(r >= 0);
}
TEST(format_proc_fd_path) {