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Loader.so+LibELF: Do not read environment variables if AT_SECURE is set

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AT_SECURE is set in the auxiliary vector when we execute setuid/setgid
programs.
In those cases, we do not want to read environment variables that
influence the logic of the dynamic loader, as they can be controlled
by the user.
This commit is contained in:
Itamar 2021-01-09 09:51:44 +02:00 committed by Andreas Kling
parent 20974b0772
commit a4b74cba0b
Notes: sideshowbarker 2024-07-19 00:02:08 +09:00 
Author: https://github.com/itamar8910
Commit: https://github.com/SerenityOS/serenity/commit/a4b74cba0b1
Pull-request: https://github.com/SerenityOS/serenity/pull/4852
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/awesomekling
3 changed files with 22 additions and 8 deletions
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22
Libraries/LibELF/DynamicLinker.cpp
View file

@ -71,6 +71,9 @@ size_t g_current_tls_offset = 0;
size_t g_total_tls_size = 0;
char** g_envp = nullptr;
LibCExitFunction g_libc_exit = nullptr;
bool g_allowed_to_check_environment_variables { false };
bool g_do_breakpoint_trap_before_entry { false };
}
DynamicObject::SymbolLookupResult DynamicLinker::lookup_global_symbol(const char* symbol_name)
@ -228,15 +231,22 @@ static NonnullRefPtr<DynamicLoader> commit_elf(const String& name)
return loader;
}
void ELF::DynamicLinker::linker_main(String&& main_program_name, int main_program_fd, int argc, char** argv, char** envp)
static void read_environment_variables()
{
g_envp = envp;
bool do_breakpoint_trap_before_entry = false;
for (char** env = envp; *env; ++env) {
for (char** env = g_envp; *env; ++env) {
if (StringView { *env } == "_LOADER_BREAKPOINT=1") {
do_breakpoint_trap_before_entry = true;
g_do_breakpoint_trap_before_entry = true;
}
}
}
void ELF::DynamicLinker::linker_main(String&& main_program_name, int main_program_fd, bool is_secure, int argc, char** argv, char** envp)
{
g_envp = envp;
g_allowed_to_check_environment_variables = !is_secure;
if (g_allowed_to_check_environment_variables)
read_environment_variables();
map_library(main_program_name, main_program_fd);
map_dependencies(main_program_name);
@ -260,7 +270,7 @@ void ELF::DynamicLinker::linker_main(String&& main_program_name, int main_progra
MainFunction main_function = (MainFunction)(entry_point);
VERBOSE("jumping to main program entry point: %p\n", main_function);
if (do_breakpoint_trap_before_entry) {
if (g_do_breakpoint_trap_before_entry) {
asm("int3");
}
int rc = main_function(argc, argv, envp);

2
Libraries/LibELF/DynamicLinker.h
View file

@ -35,7 +35,7 @@ namespace ELF {
class DynamicLinker {
public:
static DynamicObject::SymbolLookupResult lookup_global_symbol(const char* symbol);
[[noreturn]] static void linker_main(String&& main_program_name, int fd, int argc, char** argv, char** envp);
[[noreturn]] static void linker_main(String&& main_program_name, int fd, bool is_secure, int argc, char** argv, char** envp);
private:
DynamicLinker() = delete;

6
Userland/DynamicLoader/main.cpp
View file

@ -135,6 +135,7 @@ void _start(int argc, char** argv, char** envp)
int main_program_fd = -1;
String main_program_name;
bool is_secure = false;
for (; auxvp->a_type != AT_NULL; ++auxvp) {
if (auxvp->a_type == ELF::AuxiliaryValue::ExecFileDescriptor) {
main_program_fd = auxvp->a_un.a_val;
@ -142,6 +143,9 @@ void _start(int argc, char** argv, char** envp)
if (auxvp->a_type == ELF::AuxiliaryValue::ExecFilename) {
main_program_name = (const char*)auxvp->a_un.a_ptr;
}
if (auxvp->a_type == ELF::AuxiliaryValue::Secure) {
is_secure = auxvp->a_un.a_val == 1;
}
}
if (main_program_name == "/usr/lib/Loader.so") {
@ -156,7 +160,7 @@ void _start(int argc, char** argv, char** envp)
ASSERT(main_program_fd >= 0);
ASSERT(!main_program_name.is_empty());
ELF::DynamicLinker::linker_main(move(main_program_name), main_program_fd, argc, argv, envp);
ELF::DynamicLinker::linker_main(move(main_program_name), main_program_fd, is_secure, argc, argv, envp);
ASSERT_NOT_REACHED();
}
}