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rtld: avoid use of of getenv(3) for evaluating rtld env vars (LD_XXX)

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Scan through the set of environment variables during initialization and
store values in the corresponding ld_env_var_desc structure, in the
single pass at init time. This does not eliminate use of getenv(3) and
unsetenv(3) completely, but provides a foundation to do that as the next
step.

Also organize the scan in a way that makes it easier to support aliases
like LD_DEBUG vs. LD_64_DEBUG.

Suggested by:	arichardson
Reviewed by:	arichardson, markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D31545
This commit is contained in:
Konstantin Belousov 2021-08-16 15:59:05 +03:00
parent 451dc2b7cc
commit bfd4c875a1
1 changed files with 85 additions and 63 deletions
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148
libexec/rtld-elf/rtld.c
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@ -367,82 +367,105 @@ enum {
};
struct ld_env_var_desc {
char n[64];
bool unsecure;
const char *n;
char *val;
const bool unsecure;
};
#define LD_ENV_DESC(var, unsec) \
[LD_##var] = { .n = #var, .unsecure = unsec }
static struct ld_env_var_desc ld_env_vars[] = {
[LD_BIND_NOW] =
{ .n = "BIND_NOW", .unsecure = false },
[LD_PRELOAD] =
{ .n = "PRELOAD", .unsecure = true },
[LD_LIBMAP] =
{ .n = "LIBMAP", .unsecure = true },
[LD_LIBRARY_PATH] =
{ .n = "LIBRARY_PATH", .unsecure = true },
[LD_LIBRARY_PATH_FDS] =
{ .n = "LIBRARY_PATH_FDS", .unsecure = true },
[LD_LIBMAP_DISABLE] =
{ .n = "LIBMAP_DISABLE", .unsecure = true },
[LD_BIND_NOT] =
{ .n = "BIND_NOT", .unsecure = true },
[LD_DEBUG] =
{ .n = "DEBUG", .unsecure = true },
[LD_ELF_HINTS_PATH] =
{ .n = "ELF_HINTS_PATH", .unsecure = true },
[LD_LOADFLTR] =
{ .n = "LOADFLTR", .unsecure = true },
[LD_LIBRARY_PATH_RPATH] =
{ .n = "LIBRARY_PATH_RPATH", .unsecure = true },
[LD_PRELOAD_FDS] =
{ .n = "PRELOAD_FDS", .unsecure = true },
[LD_DYNAMIC_WEAK] =
{ .n = "DYNAMIC_WEAK", .unsecure = true },
[LD_TRACE_LOADED_OBJECTS] =
{ .n = "TRACE_LOADED_OBJECTS", .unsecure = false },
[LD_UTRACE] =
{ .n = "UTRACE", .unsecure = false },
[LD_DUMP_REL_PRE] =
{ .n = "DUMP_REL_PRE", .unsecure = false },
[LD_DUMP_REL_POST] =
{ .n = "DUMP_REL_POST", .unsecure = false },
[LD_TRACE_LOADED_OBJECTS_PROGNAME] =
{ .n = "TRACE_LOADED_OBJECTS_PROGNAME", .unsecure = false},
[LD_TRACE_LOADED_OBJECTS_FMT1] =
{ .n = "TRACE_LOADED_OBJECTS_FMT1", .unsecure = false},
[LD_TRACE_LOADED_OBJECTS_FMT2] =
{ .n = "TRACE_LOADED_OBJECTS_FMT2", .unsecure = false},
[LD_TRACE_LOADED_OBJECTS_ALL] =
{ .n = "TRACE_LOADED_OBJECTS_ALL", .unsecure = false},
LD_ENV_DESC(BIND_NOW, false),
LD_ENV_DESC(PRELOAD, true),
LD_ENV_DESC(LIBMAP, true),
LD_ENV_DESC(LIBRARY_PATH, true),
LD_ENV_DESC(LIBRARY_PATH_FDS, true),
LD_ENV_DESC(LIBMAP_DISABLE, true),
LD_ENV_DESC(BIND_NOT, true),
LD_ENV_DESC(DEBUG, true),
LD_ENV_DESC(ELF_HINTS_PATH, true),
LD_ENV_DESC(LOADFLTR, true),
LD_ENV_DESC(LIBRARY_PATH_RPATH, true),
LD_ENV_DESC(PRELOAD_FDS, true),
LD_ENV_DESC(DYNAMIC_WEAK, true),
LD_ENV_DESC(TRACE_LOADED_OBJECTS, false),
LD_ENV_DESC(UTRACE, false),
LD_ENV_DESC(DUMP_REL_PRE, false),
LD_ENV_DESC(DUMP_REL_POST, false),
LD_ENV_DESC(TRACE_LOADED_OBJECTS_PROGNAME, false),
LD_ENV_DESC(TRACE_LOADED_OBJECTS_FMT1, false),
LD_ENV_DESC(TRACE_LOADED_OBJECTS_FMT2, false),
LD_ENV_DESC(TRACE_LOADED_OBJECTS_ALL, false),
};
static const char *
ld_var(int idx)
{
return (ld_env_vars[idx].n);
}
static char *
ld_get_env_var(int idx)
{
return (getenv(ld_var(idx)));
return (ld_env_vars[idx].val);
}
static char *
rtld_get_env_val(char **env, const char *name, size_t name_len)
{
char **m, *n, *v;
for (m = env; *m != NULL; m++) {
n = *m;
v = strchr(n, '=');
if (v == NULL) {
/* corrupt environment? */
continue;
}
if (v - n == (ptrdiff_t)name_len &&
strncmp(name, n, name_len) == 0)
return (v + 1);
}
return (NULL);
}
static void
rtld_init_env_vars(void)
rtld_init_env_vars_for_prefix(char **env, const char *env_prefix)
{
struct ld_env_var_desc *lvd;
size_t sz;
size_t prefix_len, nlen;
char **m, *n, *v;
int i;
sz = strlen(ld_env_prefix);
for (i = 0; i < (int)nitems(ld_env_vars); i++) {
lvd = &ld_env_vars[i];
memmove(lvd->n + sz, lvd->n, strlen(lvd->n) + 1);
memcpy(lvd->n, ld_env_prefix, sz);
prefix_len = strlen(env_prefix);
for (m = env; *m != NULL; m++) {
n = *m;
if (strncmp(env_prefix, n, prefix_len) != 0) {
/* Not a rtld environment variable. */
continue;
}
n += prefix_len;
v = strchr(n, '=');
if (v == NULL) {
/* corrupt environment? */
continue;
}
for (i = 0; i < (int)nitems(ld_env_vars); i++) {
lvd = &ld_env_vars[i];
if (lvd->val != NULL) {
/* Saw higher-priority variable name already. */
continue;
}
nlen = strlen(lvd->n);
if (v - n == (ptrdiff_t)nlen &&
strncmp(lvd->n, n, nlen) == 0) {
lvd->val = v + 1;
break;
}
}
}
}
static void
rtld_init_env_vars(char **env)
{
rtld_init_env_vars_for_prefix(env, ld_env_prefix);
}
/*
* Main entry point for dynamic linking. The first argument is the
* stack pointer. The stack is expected to be laid out as described
@ -548,7 +571,7 @@ _rtld(Elf_Addr *sp, func_ptr_type *exit_proc, Obj_Entry **objp)
direct_exec = false;
md_abi_variant_hook(aux_info);
rtld_init_env_vars();
rtld_init_env_vars(env);
fd = -1;
if (aux_info[AT_EXECFD] != NULL) {
@ -667,12 +690,11 @@ _rtld(Elf_Addr *sp, func_ptr_type *exit_proc, Obj_Entry **objp)
if (!trust) {
for (i = 0; i < (int)nitems(ld_env_vars); i++) {
lvd = &ld_env_vars[i];
if (lvd->unsecure && unsetenv(lvd->n)) {
_rtld_error("environment corrupt; aborting");
rtld_die();
}
if (lvd->unsecure)
lvd->val = NULL;
}
}
ld_debug = ld_get_env_var(LD_DEBUG);
if (ld_bind_now == NULL)
ld_bind_not = ld_get_env_var(LD_BIND_NOT) != NULL;