Commit f56407fa authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by Daniel Borkmann
Browse files

bpf: Remove bpf_lsm_file_mprotect from sleepable list. 



Technically the bpf programs can sleep while attached to bpf_lsm_file_mprotect,
but such programs need to access user memory. So they're in might_fault()
category. Which means they cannot be called from file_mprotect lsm hook that
takes write lock on mm->mmap_lock.
Adjust the test accordingly.

Also add might_fault() to __bpf_prog_enter_sleepable() to catch such deadlocks early.

Fixes: 1e6c62a8 ("bpf: Introduce sleepable BPF programs")
Fixes: e68a1445 ("selftests/bpf: Add sleepable tests")
Reported-by: default avatarYonghong Song <yhs@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200831201651.82447-1-alexei.starovoitov@gmail.com
parent b69e56cf

kernel/bpf/trampoline.c

+1 −0
Original line number Diff line number Diff line
@@ -409,6 +409,7 @@ void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start) 
void notrace __bpf_prog_enter_sleepable(void)

{

	rcu_read_lock_trace();

	might_fault();

}



void notrace __bpf_prog_exit_sleepable(void)

kernel/bpf/verifier.c

+0 −1
Original line number Diff line number Diff line
@@ -11006,7 +11006,6 @@ static int check_attach_modify_return(struct bpf_prog *prog, unsigned long addr) 
/* non exhaustive list of sleepable bpf_lsm_*() functions */

BTF_SET_START(btf_sleepable_lsm_hooks)

#ifdef CONFIG_BPF_LSM

BTF_ID(func, bpf_lsm_file_mprotect)

BTF_ID(func, bpf_lsm_bprm_committed_creds)

#else

BTF_ID_UNUSED

tools/testing/selftests/bpf/progs/lsm.c

+17 −17
Original line number Diff line number Diff line
@@ -36,14 +36,10 @@ int monitored_pid = 0; 
int mprotect_count = 0;

int bprm_count = 0;



SEC("lsm.s/file_mprotect")

SEC("lsm/file_mprotect")

int BPF_PROG(test_int_hook, struct vm_area_struct *vma,

	     unsigned long reqprot, unsigned long prot, int ret)

{

	char args[64];

	__u32 key = 0;

	__u64 *value;



	if (ret != 0)

		return ret;
@@ -53,18 +49,6 @@ int BPF_PROG(test_int_hook, struct vm_area_struct *vma, 
	is_stack = (vma->vm_start <= vma->vm_mm->start_stack &&

		    vma->vm_end >= vma->vm_mm->start_stack);



	bpf_copy_from_user(args, sizeof(args), (void *)vma->vm_mm->arg_start);



	value = bpf_map_lookup_elem(&array, &key);

	if (value)

		*value = 0;

	value = bpf_map_lookup_elem(&hash, &key);

	if (value)

		*value = 0;

	value = bpf_map_lookup_elem(&lru_hash, &key);

	if (value)

		*value = 0;



	if (is_stack && monitored_pid == pid) {

		mprotect_count++;

		ret = -EPERM;
@@ -77,10 +61,26 @@ SEC("lsm.s/bprm_committed_creds") 
int BPF_PROG(test_void_hook, struct linux_binprm *bprm)

{

	__u32 pid = bpf_get_current_pid_tgid() >> 32;

	char args[64];

	__u32 key = 0;

	__u64 *value;



	if (monitored_pid == pid)

		bprm_count++;



	bpf_copy_from_user(args, sizeof(args), (void *)bprm->vma->vm_mm->arg_start);

	bpf_copy_from_user(args, sizeof(args), (void *)bprm->mm->arg_start);



	value = bpf_map_lookup_elem(&array, &key);

	if (value)

		*value = 0;

	value = bpf_map_lookup_elem(&hash, &key);

	if (value)

		*value = 0;

	value = bpf_map_lookup_elem(&lru_hash, &key);

	if (value)

		*value = 0;



	return 0;

}

SEC("lsm/task_free") /* lsm/ is ok, lsm.s/ fails */

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