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Preserve logd_fd after specialization

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Also add more comments regarding FD checks
This commit is contained in:
topjohnwu
2022-09-02 01:49:17 -07:00
parent 555a54ec53
commit 6e299018a4
4 changed files with 212 additions and 138 deletions
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51
native/src/zygisk/entry.cpp
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@@ -76,36 +76,51 @@ extern "C" void zygisk_inject_entry(void *handle) {
// The following code runs in zygote/app process
extern "C" void zygisk_log_write(int prio, const char *msg, int len) {
// If we don't have log pipe set, ask magiskd for it
// This could happen multiple times in zygote because it was closed to prevent crashing
// If we don't have the log pipe set, request magiskd for it. This could actually happen
// multiple times in the zygote daemon (parent process) because we had to close this
// file descriptor to prevent crashing.
//
// For some reason, zygote sanitizes and checks FDs *before* forking. This results in the fact
// that *every* time before zygote forks, it has to close all logging related FDs in order
// to pass FD checks, just to have it re-initialized immediately after any
// logging happens ¯\_(ツ)_/¯.
//
// To be consistent with this behavior, we also have to close the log pipe to magiskd
// to make zygote NOT crash if necessary. For nativeForkAndSpecialize, we can actually
// add this FD into fds_to_ignore to pass the check. For other cases, we accomplish this by
// hooking __android_log_close and closing it at the same time as the rest of logging FDs.
if (logd_fd < 0) {
// Change logging temporarily to prevent infinite recursion and stack overflow
android_logging();
if (int fd = zygisk_request(ZygiskRequest::GET_LOG_PIPE); fd >= 0) {
int log_pipe = -1;
if (read_int(fd) == 0) {
logd_fd = recv_fd(fd);
log_pipe = recv_fd(fd);
}
close(fd);
if (log_pipe >= 0) {
// Only re-enable zygisk logging if possible
logd_fd = log_pipe;
zygisk_logging();
}
} else {
return;
}
zygisk_logging();
}
// Block SIGPIPE
sigset_t mask;
sigset_t orig_mask;
bool sig = false;
// Make sure SIGPIPE won't crash zygote
if (logd_fd >= 0) {
sig = true;
sigemptyset(&mask);
sigaddset(&mask, SIGPIPE);
pthread_sigmask(SIG_BLOCK, &mask, &orig_mask);
}
sigemptyset(&mask);
sigaddset(&mask, SIGPIPE);
pthread_sigmask(SIG_BLOCK, &mask, &orig_mask);
magisk_log_write(prio, msg, len);
if (sig) {
timespec ts{};
sigtimedwait(&mask, nullptr, &ts);
pthread_sigmask(SIG_SETMASK, &orig_mask, nullptr);
}
// Consume SIGPIPE if exists, then restore mask
timespec ts{};
sigtimedwait(&mask, nullptr, &ts);
pthread_sigmask(SIG_SETMASK, &orig_mask, nullptr);
}
static inline bool should_load_modules(uint32_t flags) {