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Move preload_dso() to its own file and rename to sudo_preload_dso().

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It now takes an intercept fd as an optional argument instead of a
list of extra variables to add.  This lets us check whether it is
already set to the expected value (and add it if not).
sudo_intercept.so now uses sudo_preload_dso() to make sure that
LD_PRELOAD and SUDO_INTERCEPT_FD are set properly before executing.
This commit is contained in:
Todd C. Miller
2021-08-09 15:50:25 -06:00
parent 60e76e3e35
commit 9c3df47da9
7 changed files with 290 additions and 169 deletions
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126
src/exec_common.c
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@@ -36,125 +36,6 @@
#include "sudo.h"
#include "sudo_exec.h"
#ifdef RTLD_PRELOAD_VAR
/*
* Add a DSO file to LD_PRELOAD or the system equivalent.
*/
static char **
preload_dso(char *envp[], const char *dso_file, char * const extra_envp[])
{
char *preload = NULL;
int env_len, extra_len = 0;
int preload_idx = -1;
bool present = false;
# ifdef RTLD_PRELOAD_ENABLE_VAR
bool enabled = false;
# else
const bool enabled = true;
# endif
debug_decl(preload_dso, SUDO_DEBUG_UTIL);
/*
* Preload a DSO file. For a list of LD_PRELOAD-alikes, see
* http://www.fortran-2000.com/ArnaudRecipes/sharedlib.html
* XXX - need to support 32-bit and 64-bit variants
*/
/* Count entries in envp, looking for LD_PRELOAD as we go. */
for (env_len = 0; envp[env_len] != NULL; env_len++) {
if (preload_idx == -1 && strncmp(envp[env_len], RTLD_PRELOAD_VAR "=",
sizeof(RTLD_PRELOAD_VAR)) == 0) {
const char *cp = envp[env_len] + sizeof(RTLD_PRELOAD_VAR);
const char *end = cp + strlen(cp);
const char *ep;
const size_t dso_len = strlen(dso_file);
/* Check to see if dso_file is already present. */
for (cp = sudo_strsplit(cp, end, RTLD_PRELOAD_DELIM, &ep);
cp != NULL; cp = sudo_strsplit(NULL, end, RTLD_PRELOAD_DELIM,
&ep)) {
if ((size_t)(ep - cp) == dso_len) {
if (memcmp(cp, dso_file, dso_len) == 0) {
/* already present */
present = true;
break;
}
}
}
/* Save index of existing LD_PRELOAD variable. */
preload_idx = env_len;
continue;
}
# ifdef RTLD_PRELOAD_ENABLE_VAR
if (strncmp(envp[env_len], RTLD_PRELOAD_ENABLE_VAR "=", sizeof(RTLD_PRELOAD_ENABLE_VAR)) == 0) {
enabled = true;
continue;
}
# endif
}
if (extra_envp != NULL) {
for (extra_len = 0; extra_envp[extra_len] != NULL; extra_len++) {
continue;
}
}
/*
* Make a new copy of envp as needed.
* It would be nice to realloc the old envp[] but we don't know
* whether it was dynamically allocated. [TODO: plugin API]
*/
if (preload_idx == -1 || !enabled || extra_len != 0) {
const int env_size = env_len + 1 + (preload_idx == -1) + enabled + extra_len; // -V547
char **nenvp = reallocarray(NULL, env_size, sizeof(*envp));
if (nenvp == NULL)
sudo_fatalx(U_("%s: %s"), __func__, U_("unable to allocate memory"));
memcpy(nenvp, envp, env_len * sizeof(*envp));
if (extra_envp != NULL) {
for (extra_len = 0; extra_envp[extra_len] != NULL; extra_len++)
nenvp[env_len++] = extra_envp[extra_len];
}
nenvp[env_len] = NULL;
envp = nenvp;
}
/* Prepend our LD_PRELOAD to existing value or add new entry at the end. */
if (!present) {
if (preload_idx == -1) {
# ifdef RTLD_PRELOAD_DEFAULT
asprintf(&preload, "%s=%s%s%s", RTLD_PRELOAD_VAR, dso_file,
RTLD_PRELOAD_DELIM, RTLD_PRELOAD_DEFAULT);
# else
preload = sudo_new_key_val(RTLD_PRELOAD_VAR, dso_file);
# endif
if (preload == NULL) {
sudo_fatalx(U_("%s: %s"), __func__,
U_("unable to allocate memory"));
}
envp[env_len++] = preload;
envp[env_len] = NULL;
} else {
int len = asprintf(&preload, "%s=%s%s%s", RTLD_PRELOAD_VAR,
dso_file, RTLD_PRELOAD_DELIM, envp[preload_idx]);
if (len == -1) {
sudo_fatalx(U_("%s: %s"), __func__,
U_("unable to allocate memory"));
}
envp[preload_idx] = preload;
}
}
# ifdef RTLD_PRELOAD_ENABLE_VAR
if (!enabled) {
envp[env_len++] = RTLD_PRELOAD_ENABLE_VAR "=";
envp[env_len] = NULL;
}
# endif
debug_return_ptr(envp);
}
#endif /* RTLD_PRELOAD_VAR */
/*
* Disable execution of child processes in the command we are about
* to run. On systems with privilege sets, we can remove the exec
@@ -177,7 +58,7 @@ disable_execute(char *envp[], const char *dso)
#ifdef RTLD_PRELOAD_VAR
if (dso != NULL)
envp = preload_dso(envp, dso, NULL);
envp = sudo_preload_dso(envp, dso, -1);
#endif /* RTLD_PRELOAD_VAR */
debug_return_ptr(envp);
@@ -191,7 +72,6 @@ static char **
enable_intercept(char *envp[], const char *dso, int intercept_fd)
{
#ifdef RTLD_PRELOAD_VAR
char *env_add[] = { NULL, NULL };
debug_decl(enable_intercept, SUDO_DEBUG_UTIL);
if (dso == NULL)
@@ -204,9 +84,7 @@ enable_intercept(char *envp[], const char *dso, int intercept_fd)
if (intercept_fd == -1)
sudo_fatal("%s", U_("unable to dup intercept fd"));
}
if (asprintf(&env_add[0], "SUDO_INTERCEPT_FD=%d", intercept_fd) == -1)
debug_return_ptr(NULL);
envp = preload_dso(envp, dso, env_add);
envp = sudo_preload_dso(envp, dso, intercept_fd);
#else
/* Intercept not supported, envp unchanged. */
if (intercept_fd != -1)