Merge branch 'bpf: fix NULL dereference during extable search'

Krister Johansen says:

====================
Hi,
Enclosed are a pair of patches for an oops that can occur if an exception is
generated while a bpf subprogram is running.  One of the bpf_prog_aux entries
for the subprograms are missing an extable.  This can lead to an exception that
would otherwise be handled turning into a NULL pointer bug.

These changes were tested via the verifier and progs selftests and no
regressions were observed.

Changes from v4:
- Ensure that num_exentries is copied to prog->aux from func[0] (Feedback from
  Ilya Leoshkevich)

Changes from v3:
- Selftest style fixups (Feedback from Yonghong Song)
- Selftest needs to assert that test bpf program executed (Feedback from
  Yonghong Song)
- Selftest should combine open and load using open_and_load (Feedback from
  Yonghong Song)

Changes from v2:
- Insert only the main program's kallsyms (Feedback from Yonghong Song and
  Alexei Starovoitov)
- Selftest should use ASSERT instead of CHECK (Feedback from Yonghong Song)
- Selftest needs some cleanup (Feedback from Yonghong Song)
- Switch patch order (Feedback from Alexei Starovoitov)

Changes from v1:
- Add a selftest (Feedback From Alexei Starovoitov)
- Move to a 1-line verifier change instead of searching multiple extables
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 5 insertions, 2 deletions

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 0dd8adc7a159..cf5f230360f5 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -17217,9 +17217,10 @@ static int jit_subprogs(struct bpf_verifier_env *env)
 	}
 
 	/* finally lock prog and jit images for all functions and
-	 * populate kallsysm
+	 * populate kallsysm. Begin at the first subprogram, since
+	 * bpf_prog_load will add the kallsyms for the main program.
 	 */
-	for (i = 0; i < env->subprog_cnt; i++) {
+	for (i = 1; i < env->subprog_cnt; i++) {
 		bpf_prog_lock_ro(func[i]);
 		bpf_prog_kallsyms_add(func[i]);
 	}
@@ -17245,6 +17246,8 @@ static int jit_subprogs(struct bpf_verifier_env *env)
 	prog->jited = 1;
 	prog->bpf_func = func[0]->bpf_func;
 	prog->jited_len = func[0]->jited_len;
+	prog->aux->extable = func[0]->aux->extable;
+	prog->aux->num_exentries = func[0]->aux->num_exentries;
 	prog->aux->func = func;
 	prog->aux->func_cnt = env->subprog_cnt;
 	bpf_prog_jit_attempt_done(prog);