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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: 1e6c62a882 ("bpf: Introduce sleepable BPF programs")
Fixes: e68a144547 ("selftests/bpf: Add sleepable tests")
Reported-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200831201651.82447-1-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov 2020-08-31 13:16:51 -07:00 committed by Daniel Borkmann
parent b69e56cf76
commit f56407fa6e
3 changed files with 18 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
kernel/bpf/trampoline.c
View File

@ -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)

1
kernel/bpf/verifier.c
View File

@ -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

34
tools/testing/selftests/bpf/progs/lsm.c
View File

@ -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 */