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user: fail closed when supplementary groups cannot be set #288

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5 changes: 5 additions & 0 deletions Makefile
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Original file line number Diff line number Diff line change
Expand Up @@ -152,6 +152,11 @@ test: $(BIN)
# --- Basic sanity tests ---
$(call run_test, ./nsjail -q -Mo --chroot / --user 99999 --group 99999 -- /bin/true, 0)
$(call run_test, ./nsjail -q -Mo --chroot / --user 99999 --group 99999 -- /bin/false, 1)
$(call run_test, strace -f -qq -e inject=setgroups:error=EPERM ./nsjail -q -Mo --disable_clone_newuser --chroot / --user 99999 --group 99999 -- /bin/true, 255)
ifeq ($(UID),0)
$(call run_test, setpriv --reuid 1000 --regid 1000 --groups 1234 -- ./nsjail -q -Mo --user 65534 --group 65534 --disable_clone_newnet --disable_clone_newcgroup --disable_clone_newns --disable_clone_newpid --disable_clone_newipc --disable_clone_newuts --disable_proc -- /bin/true, 255)
$(call run_test, setpriv --reuid 1000 --regid 1000 --clear-groups -- ./nsjail -q -Mo --user 65534 --group 65534 --disable_clone_newnet --disable_clone_newcgroup --disable_clone_newns --disable_clone_newpid --disable_clone_newipc --disable_clone_newuts --disable_proc -- /bin/true, 0)
endif
$(call run_test, ./nsjail --config tests/seccomp.cfg -q -t 2 -- /bin/bash -c 'strace -o /dev/null /bin/true || exit 77', 77)
$(call run_test, ./nsjail --config tests/basic.cfg -q -t 2 -- /bin/bash -c 'strace -o /dev/null /bin/true && exit 77', 77)
$(call run_test, ./nsjail --config tests/pasta-nat.cfg -q -t 3 -- /bin/bash -c 'sleep 0.2; ping -W 1 -c 1 8.8.8.8 && exit 77', 77)
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26 changes: 23 additions & 3 deletions user.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -102,12 +102,16 @@ static bool hasGidMapSelf(nsj_t* nsj) {
return false;
}

static bool shouldDenySetGroups(nsj_t* nsj) {
return nsj->njc.clone_newuser() && nsj->orig_euid != 0 && hasGidMapSelf(nsj);
}

static bool setGroupsDeny(nsj_t* nsj, pid_t pid) {
/*
* No need to write 'deny' to /proc/pid/setgroups if our euid==0, as writing to
* uid_map/gid_map will succeed anyway
*/
if (!nsj->njc.clone_newuser() || nsj->orig_euid == 0 || !hasGidMapSelf(nsj)) {
if (!shouldDenySetGroups(nsj)) {
return true;
}

Expand Down Expand Up @@ -288,11 +292,27 @@ bool initNsFromChild(nsj_t* nsj) {

LOG_D("setgroups(%zu, %s)", groups.size(), groupsString.c_str());
if (setgroups(groups.size(), groups.data()) == -1) {
/* Indicate error if specific groups were requested */
if (groups.size() > 0) {
const int setgroupsErrno = errno;
/* EPERM is expected after the parent writes "deny" to /proc/pid/setgroups. */
if (!shouldDenySetGroups(nsj) || setgroupsErrno != EPERM) {
errno = setgroupsErrno;
PLOG_E("setgroups(%zu, %s) failed", groups.size(), groupsString.c_str());
return false;
}

const int remainingGroups = getgroups(0, nullptr);
if (remainingGroups == -1) {
PLOG_E("getgroups(0, nullptr) failed");
return false;
}
if (remainingGroups != 0) {
errno = setgroupsErrno;
PLOG_E("setgroups(%zu, %s) failed and %d supplementary group(s) remain",
groups.size(), groupsString.c_str(), remainingGroups);
return false;
}

errno = setgroupsErrno;
PLOG_D("setgroups(%zu, %s) failed", groups.size(), groupsString.c_str());
}

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