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https://github.com/Droid-Deck/DroidDeck.git
synced 2026-11-11 02:51:10 +00:00
maxjivi05
8a6877423e
Every Electron AppImage hung without a window or crashed at its first page. Four causes, each enough on its own: - The session preload's hooks found the real functions with dlsym(RTLD_NEXT). Before glibc 2.34 a thread's first dlsym callocs, and Chromium's PartitionAlloc calls syscall() from inside its first malloc: the allocator waited for itself. On older glibc (the x86 runtime's 2.31) next.c now walks the libraries after the preload with no allocation and picks each function's default version, as glibc 2.36 does; the old lookup handed realpath() and posix_spawn() their compat versions, and realpath(path, NULL) failed. arm64 keeps dlsym. - libpci's sysfs backend exits when /sys/bus/pci/devices is listable but a device's files are not (a RedMagic's PCIe root port), taking every Chromium GPU process with it. An empty directory is bound over it on devices where that happens. - FEX_OUTPUTLOG=stderr made FEX log to its own duplicate of descriptor 2. Chromium dup2()s its IPC socket onto that low number in each child it starts, then lists /proc/self/fd, which FEX logs into the socket. Empty, FEX writes to descriptor 2 itself. - The tracer preload served every /proc/<pid>/status as a memfd, which is open for writing. Chromium hands each renderer its status as a read-only file and checks that it is one. Only a process's own status (pid, tid, self, thread-self) is rewritten now.
130 lines
4.1 KiB
Python
130 lines
4.1 KiB
Python
from pathlib import Path
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import shutil
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import subprocess
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import sys
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import tempfile
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import unittest
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PRELOAD = Path(__file__).resolve().parents[1] / "linuxfs/preload"
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PROBE = r"""
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#define _GNU_SOURCE
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#include <dlfcn.h>
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void *bl_next(const char *name) __attribute__((visibility("hidden")));
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void *__real_dlsym(void *handle, const char *name);
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/* Lookups the walk left to dlsym. */
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static int walking;
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static long passed_on;
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void *__wrap_dlsym(void *handle, const char *name) {
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passed_on += walking;
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return __real_dlsym(handle, name);
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}
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void *probe_walk(const char *name) {
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walking = 1;
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void *found = bl_next(name);
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walking = 0;
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return found;
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}
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void *probe_dlsym(const char *name) { return dlsym(RTLD_NEXT, name); }
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long probe_passed_on(void) { return passed_on; }
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"""
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# Counts the allocations a thread makes, as an allocator that is still starting up would see them.
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COUNT = r"""
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#include <stddef.h>
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extern void *__libc_malloc(size_t);
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extern void *__libc_calloc(size_t, size_t);
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extern void *__libc_realloc(void *, size_t);
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static __thread long made;
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void *malloc(size_t size) { made++; return __libc_malloc(size); }
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void *calloc(size_t count, size_t size) { made++; return __libc_calloc(count, size); }
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void *realloc(void *old, size_t size) { made++; return __libc_realloc(old, size); }
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void count_reset(void) { made = 0; }
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long count_get(void) { return made; }
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"""
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PROGRAM = r"""
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#include <pthread.h>
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#include <stdio.h>
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void *probe_walk(const char *name);
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void *probe_dlsym(const char *name);
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long probe_passed_on(void);
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void count_reset(void);
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long count_get(void);
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static void *first_lookup(void *made) {
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long before = probe_passed_on();
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count_reset();
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void *found = probe_walk("openat");
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((long *)made)[0] = found ? count_get() : -1;
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((long *)made)[1] = probe_passed_on() - before;
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return NULL;
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}
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int main(int argc, char **argv) {
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int differ = 0;
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for (int i = 1; i < argc; i++) {
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void *walked = probe_walk(argv[i]), *found = probe_dlsym(argv[i]);
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if (walked != found) {
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printf("%s: %p, dlsym %p\n", argv[i], walked, found);
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differ = 1;
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}
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}
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long made[2] = {0, 0};
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pthread_t thread;
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pthread_create(&thread, NULL, first_lookup, made);
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pthread_join(thread, NULL);
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printf("allocations %ld, left to dlsym %ld\n", made[0], made[1]);
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return differ;
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}
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"""
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NAMES = ["open", "openat", "read", "recvmsg", "syscall", "close_range", "fstatat", "stat", "pthread_create",
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"dlopen", "malloc", "calloc", "memcpy", "strlen", "environ", "no_such_symbol"]
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@unittest.skipUnless(sys.platform.startswith("linux") and shutil.which("cc"), "needs Linux and a C compiler")
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class NextTest(unittest.TestCase):
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"""bl_next built as on glibc before 2.34, where the walk replaces dlsym(RTLD_NEXT)."""
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@classmethod
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def setUpClass(cls):
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cls.build = tempfile.TemporaryDirectory()
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build = Path(cls.build.name)
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(build / "probe.c").write_text(PROBE)
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(build / "count.c").write_text(COUNT)
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(build / "program.c").write_text(PROGRAM)
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cls.count = build / "libcount.so"
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cls.program = build / "program"
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subprocess.run(["cc", "-shared", "-fPIC", "-O2", "-DNEXT_TEST", "-Wl,--wrap=dlsym", "-o", str(build / "libprobe.so"),
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str(build / "probe.c"), str(PRELOAD / "next.c"), "-ldl"], check=True)
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subprocess.run(["cc", "-shared", "-fPIC", "-O2", "-o", str(cls.count), str(build / "count.c")], check=True)
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subprocess.run(["cc", "-O2", "-pthread", "-o", str(cls.program), str(build / "program.c"),
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str(build / "libprobe.so"), str(cls.count), "-Wl,-rpath," + str(build)], check=True)
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@classmethod
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def tearDownClass(cls):
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cls.build.cleanup()
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def run_program(self):
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return subprocess.run([str(self.program)] + NAMES, capture_output=True, text=True)
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def test_finds_what_dlsym_finds(self):
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result = self.run_program()
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self.assertEqual(0, result.returncode, result.stdout + result.stderr)
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def test_a_threads_first_lookup_walks_and_allocates_nothing(self):
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self.assertIn("allocations 0, left to dlsym 0\n", self.run_program().stdout)
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if __name__ == "__main__":
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unittest.main()
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