forked from rpms/glibc
103 lines
3.2 KiB
C
103 lines
3.2 KiB
C
/*
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To build:
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With system libc:
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gcc -o libdl_bug libdl_bug.c -ldl -pthread
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With custom libc
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libc_dir=/path/to/glibc/install
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gcc -o libdl_bug libdl_bug.c -L$libc_dir/lib -Wl,--rpath=$libc_dir/lib \
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-Wl,--dynamic-linker=$libc_dir/lib/ld-linux-x86-64.so.2 -ldl -pthread
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./libdl_bug bad_free is just a sanity check that valgrind will notice if
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|&do_not_free_this| is accidentally passed to |free|.
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Otherwise, this tool will allocate a |pthread_key_t| (which will likely be zero)
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and store |&do_not_free_this| in it. The |pthread_key_t| has no destructor, so
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this is perfectly valid.
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It will then optionally call |dlerror| (pass dlerror vs no_dlerror to the tool),
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and then return from |main| cleanly. At this point, when running under valgrind,
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vg_preloaded.c will call |__libc_freeres|.
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In glibc after 2827ab990aefbb0e53374199b875d98f116d6390 (2.28 and later),
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|__libc_freeres| will call |__libdl_freeres|, which calls |free_key_mem| in
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dlerror.c. That function cleans up |dlerror|'s thread-local state, but has a
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bug: if nothing has called |dlerror|, there is no thread-local state and the
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|pthread_key_t| is uninitialized! It then blindly calls |free| on the zero key,
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and hits our |&do_not_free_this|. That results in an error in valgrind:
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$ valgrind -q ./libdl_bug dlerror
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Initializing a pthread_key_t.
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key = 0
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Setting thread local to &do_not_free_this.
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Calling dlerror.
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Exiting
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$ valgrind -q ./libdl_bug no_dlerror
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Initializing a pthread_key_t.
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key = 0
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Setting thread local to &do_not_free_this.
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Exiting
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==139993== Invalid free() / delete / delete[] / realloc()
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==139993== at 0x4C2FFA8: free (vg_replace_malloc.c:540)
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==139993== by 0x4E3D6D9: free_key_mem (dlerror.c:223)
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==139993== by 0x4E3D6D9: __dlerror_main_freeres (dlerror.c:239)
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==139993== by 0x53BFDC9: __libc_freeres (in /[...]/lib/libc-2.29.9000.so)
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==139993== by 0x4A296DB: _vgnU_freeres (vg_preloaded.c:77)
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==139993== by 0x5296381: __run_exit_handlers (exit.c:132)
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==139993== by 0x52963A9: exit (exit.c:139)
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==139993== by 0x528105D: (below main) (libc-start.c:342)
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==139993== Address 0x30a08c is 0 bytes inside data symbol "do_not_free_this"
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==139993==
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*/
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#include <dlfcn.h>
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#include <pthread.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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static void usage(const char *prog_name) {
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fprintf(stderr, "Usage: %s [bad_free|no_dlerror|dlerror]\n", prog_name);
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exit(1);
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}
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static int do_not_free_this;
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static pthread_key_t key;
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int main(int argc, char **argv) {
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if (argc != 2) {
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usage(argv[0]);
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}
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if (strcmp(argv[1], "bad_free") == 0) {
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printf("Calling free(&do_not_free_this). Valgrind should notice.\n");
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free(&do_not_free_this);
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} else if (strcmp(argv[1], "no_dlerror") == 0 ||
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strcmp(argv[1], "dlerror") == 0) {
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printf("Initializing a pthread_key_t.\n");
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if (pthread_key_create(&key, NULL)) {
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perror("pthread_key_create");
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exit(1);
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}
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printf("key = %d\n", key);
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printf("Setting thread local to &do_not_free_this.\n");
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if (pthread_setspecific(key, &do_not_free_this) != 0) {
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perror("pthread_setspecific");
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exit(1);
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}
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if (strcmp(argv[1], "dlerror") == 0) {
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printf("Calling dlerror.\n");
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dlerror();
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}
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} else {
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usage(argv[0]);
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}
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printf("Exiting\n");
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return 0;
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}
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