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Merge pull request #22800 from poettering/safe-ptr-sub1

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Add helper macro PTR_SUB1() to deal with backwards iteration through arrays without UB
This commit is contained in:
Yu Watanabe 2022-03-24 06:34:09 +09:00 committed by GitHub
commit bc7a6ee4af
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11 changed files with 85 additions and 57 deletions
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16
src/basic/macro.h
View File

@ -463,4 +463,20 @@ typedef struct {
assert_cc(sizeof(dummy_t) == 0);
/* A little helper for subtracting 1 off a pointer in a safe UB-free way. This is intended to be used for for
* loops that count down from a high pointer until some base. A naive loop would implement this like this:
*
* for (p = end-1; p >= base; p--) …
*
* But this is not safe because p before the base is UB in C. With this macro the loop becomes this instead:
*
* for (p = PTR_SUB1(end, base); p; p = PTR_SUB1(p, base)) …
*
* And is free from UB! */
#define PTR_SUB1(p, base) \
({ \
typeof(p) _q = (p); \
_q && _q > (base) ? &_q[-1] : NULL; \
})
#include "log.h"

16
src/basic/path-util.c
View File

@ -929,8 +929,9 @@ int path_find_first_component(const char **p, bool accept_dot_dot, const char **
static const char *skip_slash_or_dot_backward(const char *path, const char *q) {
assert(path);
assert(!q || q >= path);
for (; q >= path; q--) {
for (; q; q = PTR_SUB1(q, path)) {
if (*q == '/')
continue;
if (q > path && strneq(q - 1, "/.", 2))
@ -995,7 +996,7 @@ int path_find_last_component(const char *path, bool accept_dot_dot, const char *
q = path + strlen(path) - 1;
q = skip_slash_or_dot_backward(path, q);
if ((q < path) || /* the root directory */
if (!q || /* the root directory */
(q == path && *q == '.')) { /* path is "." or "./" */
if (next)
*next = path;
@ -1006,10 +1007,10 @@ int path_find_last_component(const char *path, bool accept_dot_dot, const char *
last_end = q + 1;
while (q >= path && *q != '/')
q--;
while (q && *q != '/')
q = PTR_SUB1(q, path);
last_begin = q + 1;
last_begin = q ? q + 1 : path;
len = last_end - last_begin;
if (len > NAME_MAX)
@ -1019,10 +1020,7 @@ int path_find_last_component(const char *path, bool accept_dot_dot, const char *
if (next) {
q = skip_slash_or_dot_backward(path, q);
if (q < path)
*next = path;
else
*next = q + 1;
*next = q ? q + 1 : path;
}
if (ret)

2
src/basic/strv.h
View File

@ -134,7 +134,7 @@ bool strv_overlap(char * const *a, char * const *b) _pure_;
_len > 0 ? h + _len - 1 : NULL; \
}); \
(s = i); \
i > h ? i-- : (i = NULL))
i = PTR_SUB1(i, h))
#define STRV_FOREACH_BACKWARDS(s, l) \
_STRV_FOREACH_BACKWARDS(s, l, UNIQ_T(h, UNIQ), UNIQ_T(i, UNIQ))

12
src/core/namespace.c
View File

@ -771,22 +771,20 @@ static void drop_nop(MountEntry *m, size_t *n) {
/* Only suppress such subtrees for READONLY, READWRITE and READWRITE_IMPLICIT entries */
if (IN_SET(f->mode, READONLY, READWRITE, READWRITE_IMPLICIT)) {
MountEntry *p;
bool found = false;
MountEntry *found = NULL;
/* Now let's find the first parent of the entry we are looking at. */
for (p = t-1; p >= m; p--) {
for (MountEntry *p = PTR_SUB1(t, m); p; p = PTR_SUB1(p, m))
if (path_startswith(mount_entry_path(f), mount_entry_path(p))) {
found = true;
found = p;
break;
}
}
/* We found it, let's see if it's the same mode, if so, we can drop this entry */
if (found && p->mode == f->mode) {
if (found && found->mode == f->mode) {
log_debug("%s (%s) is made redundant by %s (%s)",
mount_entry_path(f), mount_mode_to_string(f->mode),
mount_entry_path(p), mount_mode_to_string(p->mode));
mount_entry_path(found), mount_mode_to_string(found->mode));
mount_entry_done(f);
continue;
}

22
src/libsystemd/sd-device/sd-device.c
View File

@ -810,32 +810,26 @@ int device_set_subsystem(sd_device *device, const char *subsystem) {
int device_set_drivers_subsystem(sd_device *device) {
_cleanup_free_ char *subsystem = NULL;
const char *syspath, *drivers, *p;
const char *devpath, *drivers, *p;
int r;
assert(device);
r = sd_device_get_syspath(device, &syspath);
r = sd_device_get_devpath(device, &devpath);
if (r < 0)
return r;
drivers = strstr(syspath, "/drivers/");
drivers = strstr(devpath, "/drivers/");
if (!drivers)
return -EINVAL;
for (p = drivers - 1; p >= syspath; p--)
if (*p == '/')
break;
if (p <= syspath)
/* syspath does not start with /sys/ ?? */
return -EINVAL;
p++;
if (p >= drivers)
/* refuse duplicated slashes */
r = path_find_last_component(devpath, false, &drivers, &p);
if (r < 0)
return r;
if (r == 0)
return -EINVAL;
subsystem = strndup(p, drivers - p);
subsystem = strndup(p, r);
if (!subsystem)
return -ENOMEM;

15
src/libsystemd/sd-device/test-sd-device.c
View File

@ -12,7 +12,8 @@
#include "time-util.h"
static void test_sd_device_one(sd_device *d) {
const char *syspath, *subsystem, *val;
_cleanup_(sd_device_unrefp) sd_device *device_from_id = NULL;
const char *syspath, *subsystem, *id, *val;
dev_t devnum;
usec_t usec;
int i, r;
@ -57,7 +58,17 @@ static void test_sd_device_one(sd_device *d) {
r = sd_device_get_property_value(d, "ID_NET_DRIVER", &val);
assert_se(r >= 0 || r == -ENOENT);
log_info("syspath:%s subsystem:%s initialized:%s", syspath, strna(subsystem), yes_no(i));
r = device_get_device_id(d, &id);
assert_se(r >= 0);
r = sd_device_new_from_device_id(&device_from_id, id);
assert_se(r >= 0);
r = sd_device_get_syspath(device_from_id, &val);
assert_se(r >= 0);
assert_se(streq(syspath, val));
log_info("syspath:%s subsystem:%s id:%s initialized:%s", syspath, strna(subsystem), id, yes_no(i));
}
TEST(sd_device_enumerator_devices) {

3
src/libudev/libudev-list.c
View File

@ -152,7 +152,6 @@ struct udev_list_entry *udev_list_get_entry(struct udev_list *list) {
else {
_cleanup_free_ struct udev_list_entry **buf = NULL;
struct udev_list_entry *entry, **p;
size_t j;
buf = new(struct udev_list_entry *, n);
if (!buf)
@ -164,7 +163,7 @@ struct udev_list_entry *udev_list_get_entry(struct udev_list *list) {
typesafe_qsort(buf, n, udev_list_entry_compare_func);
for (j = n; j > 0; j--)
for (size_t j = n; j > 0; j--)
LIST_PREPEND(entries, list->entries, buf[j-1]);
}

15
src/login/logind-seat.c
View File

@ -321,24 +321,19 @@ int seat_switch_to_next(Seat *s) {
}
int seat_switch_to_previous(Seat *s) {
unsigned start, i;
Session *session;
if (MALLOC_ELEMENTSOF(s->positions) == 0)
return -EINVAL;
start = 1;
if (s->active && s->active->position > 0)
start = s->active->position;
size_t start = s->active && s->active->position > 0 ? s->active->position : 1;
for (i = start - 1; i > 0; --i) {
session = seat_get_position(s, i);
for (size_t i = start - 1; i > 0; i--) {
Session *session = seat_get_position(s, i);
if (session)
return session_activate(session);
}
for (i = MALLOC_ELEMENTSOF(s->positions) - 1; i > start; --i) {
session = seat_get_position(s, i);
for (size_t i = MALLOC_ELEMENTSOF(s->positions) - 1; i > start; i--) {
Session *session = seat_get_position(s, i);
if (session)
return session_activate(session);
}

16
src/shared/dns-domain.c
View File

@ -168,24 +168,18 @@ int dns_label_unescape_suffix(const char *name, const char **label_terminal, cha
/* Skip current terminal character (and accept domain names ending it ".") */
if (*terminal == 0)
terminal--;
terminal = PTR_SUB1(terminal, name);
if (terminal >= name && *terminal == '.')
terminal--;
terminal = PTR_SUB1(terminal, name);
/* Point name to the last label, and terminal to the preceding terminal symbol (or make it a NULL pointer) */
for (;;) {
if (terminal < name) {
/* Reached the first label, so indicate that there are no more */
terminal = NULL;
break;
}
while (terminal) {
/* Find the start of the last label */
if (*terminal == '.') {
const char *y;
unsigned slashes = 0;
for (y = terminal - 1; y >= name && *y == '\\'; y--)
for (y = PTR_SUB1(terminal, name); y && *y == '\\'; y = PTR_SUB1(y, name))
slashes++;
if (slashes % 2 == 0) {
@ -198,7 +192,7 @@ int dns_label_unescape_suffix(const char *name, const char **label_terminal, cha
}
}
terminal--;
terminal = PTR_SUB1(terminal, name);
}
r = dns_label_unescape(&name, dest, sz, 0);

23
src/test/test-macro.c
View File

@ -433,4 +433,27 @@ TEST(DECIMAL_STR_MAX) {
assert_se(DECIMAL_STR_MAX(uint64_t) == DECIMAL_STR_WIDTH(u64_longest)+1);
}
TEST(PTR_SUB1) {
static const uint64_t x[4] = { 2, 3, 4, 5 };
const uint64_t *p;
p = x + ELEMENTSOF(x)-1;
assert_se(*p == 5);
p = PTR_SUB1(p, x);
assert_se(*p == 4);
p = PTR_SUB1(p, x);
assert_se(*p == 3);
p = PTR_SUB1(p, x);
assert_se(*p == 2);
p = PTR_SUB1(p, x);
assert_se(!p);
p = PTR_SUB1(p, x);
assert_se(!p);
}
DEFINE_TEST_MAIN(LOG_INFO);

2
src/udev/udev-rules.c
View File

@ -1830,7 +1830,7 @@ static int udev_rule_apply_token_to_event(
bool found = false;
/* Drop the last line. */
for (char *p = buf + strlen(buf) - 1; p >= buf; p--)
for (char *p = PTR_SUB1(buf + strlen(buf), buf); p; p = PTR_SUB1(p, buf))
if (strchr(NEWLINE, *p)) {
*p = '\0';
found = true;