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Fix the replacement for shmget in Windows #9946

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Fix the replacement for shmget in Windows #9946

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8db6bd5
Fix the replacement for shmget in Windows
TysonAndre Nov 13, 2022
89e24a5
wip
TysonAndre Nov 14, 2022
21efeec
Address review comments
TysonAndre Nov 15, 2022
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33 changes: 33 additions & 0 deletions TSRM/tsrm_win32.c
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,7 @@
#include "tsrm_win32.h"
#include "zend_virtual_cwd.h"
#include "win32/ioutil.h"
#include "win32/winutil.h"

#ifdef ZTS
static ts_rsrc_id win32_globals_id;
Expand Down Expand Up @@ -613,6 +614,22 @@ TSRM_API int pclose(FILE *stream)
#define DESCRIPTOR_PREFIX "TSRM_SHM_DESCRIPTOR:"
#define INT_MIN_AS_STRING "-2147483648"


#define TSRM_BASE_SHM_KEY_ADDRESS 0x20000000
/* Returns a number between 0x2000_0000 and 0x3fff_ffff. On Windows, key_t is int. */
static key_t tsrm_choose_random_shm_key(key_t prev_key) {
unsigned char buf[4];
if (php_win32_get_random_bytes(buf, 4) != SUCCESS) {
return prev_key + 2;
}
uint32_t n =
((uint32_t)(buf[0]) << 24) |
(((uint32_t)buf[1]) << 16) |
(((uint32_t)buf[2]) << 8) |
(((uint32_t)buf[3]));
return (n & 0x1fffffff) + TSRM_BASE_SHM_KEY_ADDRESS;
}

TSRM_API int shmget(key_t key, size_t size, int flags)
{/*{{{*/
shm_pair *shm;
Expand All @@ -626,6 +643,9 @@ TSRM_API int shmget(key_t key, size_t size, int flags)

shm_handle = OpenFileMapping(FILE_MAP_ALL_ACCESS, FALSE, shm_segment);
info_handle = OpenFileMapping(FILE_MAP_ALL_ACCESS, FALSE, shm_info);
} else {
/* IPC_PRIVATE always creates a new segment even if IPC_CREAT flag isn't passed. */
flags |= IPC_CREAT;
}

if (!shm_handle && !info_handle) {
Expand Down Expand Up @@ -662,6 +682,19 @@ TSRM_API int shmget(key_t key, size_t size, int flags)
}
}

if (key == IPC_PRIVATE) {
/* This should call shm_get with a brand new key id that isn't used yet. See https://man7.org/linux/man-pages/man2/shmget.2.html
* Because extensions such as shmop/sysvshm can be used in userland to attach to shared memory segments, use unpredictable high positive numbers to avoid accidentally conflicting with userland. */
key = tsrm_choose_random_shm_key(TSRM_BASE_SHM_KEY_ADDRESS);
for (shm_pair *ptr = TWG(shm); ptr < (TWG(shm) + TWG(shm_size)); ptr++) {
if (ptr->descriptor && ptr->descriptor->shm_perm.key == key) {
key = tsrm_choose_random_shm_key(key);
ptr = TWG(shm);
continue;
}
}
}

shm = shm_get(key, NULL);
if (!shm) {
CloseHandle(shm_handle);
Expand Down