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Do not use std::random_device

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Directly read from urandom instead of using std::random_device.
libc++ will use iostream under-the-hood, which brings significant
binary size increase that is not welcomed, especially in magiskinit.
This commit is contained in:
topjohnwu 2019-07-14 21:56:21 -07:00
parent 41045b62dc
commit 52fd508fea
2 changed files with 9 additions and 9 deletions
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2
native/jni/init/rootdir.cpp
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@ -48,7 +48,7 @@ static void patch_init_rc(FILE *rc) {
fprintf(rc, "%s", line.data());
return true;
});
char pfd_svc[32], ls_svc[32], bc_svc[32];
char pfd_svc[16], ls_svc[16], bc_svc[16];
gen_rand_str(pfd_svc, sizeof(pfd_svc));
gen_rand_str(ls_svc, sizeof(ls_svc));
gen_rand_str(bc_svc, sizeof(bc_svc));

16
native/jni/utils/misc.cpp
View File

@ -53,16 +53,16 @@ int fork_no_zombie() {
constexpr char ALPHANUM[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
static bool seeded = false;
static std::mt19937 gen;
static std::uniform_int_distribution<int> dist(0, sizeof(ALPHANUM) - 1);
static std::uniform_int_distribution<int> dist(0, sizeof(ALPHANUM) - 2);
void gen_rand_str(char *buf, int len, bool varlen) {
if (!seeded) {
if (access("/dev/urandom", F_OK) == 0) {
std::random_device rdev;
gen.seed(rdev());
} else {
// In magiskinit
gen.seed(time(nullptr));
}
if (access("/dev/urandom", F_OK) != 0)
mknod("/dev/urandom", 0600 | S_IFCHR, makedev(1, 9));
int fd = xopen("/dev/urandom", O_RDONLY | O_CLOEXEC);
unsigned seed;
xxread(fd, &seed, sizeof(seed));
gen.seed(seed);
close(fd);
seeded = true;
}
if (varlen) {