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Kernel: Add Credentials to hold a set of user and group IDs

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This patch adds a new object to hold a Process's user credentials:

- UID, EUID, SUID
- GID, EGID, SGID, extra GIDs

Credentials are immutable and child processes initially inherit the
Credentials object from their parent.

Whenever a process changes one or more of its user/group IDs, a new
Credentials object is constructed.

Any code that wants to inspect and act on a set of credentials can now
do so without worrying about data races.
This commit is contained in:
Andreas Kling 2022-08-20 18:25:54 +02:00
parent bec314611d
commit 122d7d9533
11 changed files with 366 additions and 128 deletions
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56
Kernel/Syscalls/execve.cpp
View file

@ -495,6 +495,42 @@ ErrorOr<void> Process::do_exec(NonnullLockRefPtr<OpenFileDescription> main_progr
if (has_interpreter)
main_program_fd_allocation = TRY(allocate_fd());
auto old_credentials = this->credentials();
auto new_credentials = old_credentials;
bool executable_is_setid = false;
if (!(main_program_description->custody()->mount_flags() & MS_NOSUID)) {
auto main_program_metadata = main_program_description->metadata();
auto new_euid = old_credentials->euid();
auto new_egid = old_credentials->egid();
auto new_suid = old_credentials->suid();
auto new_sgid = old_credentials->sgid();
if (main_program_metadata.is_setuid()) {
executable_is_setid = true;
new_euid = main_program_metadata.uid;
new_suid = main_program_metadata.uid;
}
if (main_program_metadata.is_setgid()) {
executable_is_setid = true;
new_egid = main_program_metadata.gid;
new_sgid = main_program_metadata.gid;
}
if (executable_is_setid) {
new_credentials = TRY(Credentials::create(
old_credentials->uid(),
old_credentials->gid(),
new_euid,
new_egid,
new_suid,
new_sgid,
old_credentials->extra_gids()));
}
}
// We commit to the new executable at this point. There is no turning back!
// Prevent other processes from attaching to us with ptrace while we're doing this.
@ -506,24 +542,10 @@ ErrorOr<void> Process::do_exec(NonnullLockRefPtr<OpenFileDescription> main_progr
kill_threads_except_self();
bool executable_is_setid = false;
if (!(main_program_description->custody()->mount_flags() & MS_NOSUID)) {
auto main_program_metadata = main_program_description->metadata();
if (main_program_metadata.is_setuid()) {
executable_is_setid = true;
ProtectedDataMutationScope scope { *this };
m_protected_values.euid = main_program_metadata.uid;
m_protected_values.suid = main_program_metadata.uid;
}
if (main_program_metadata.is_setgid()) {
executable_is_setid = true;
ProtectedDataMutationScope scope { *this };
m_protected_values.egid = main_program_metadata.gid;
m_protected_values.sgid = main_program_metadata.gid;
}
{
ProtectedDataMutationScope scope { *this };
m_protected_values.credentials = move(new_credentials);
}
set_dumpable(!executable_is_setid);
// We make sure to enter the new address space before destroying the old one.