From: Jiri Olsa <olsajiri@xxxxxxxxx>
The following case can cause a crash due to missing attach_btf:
1) load rawtp program
2) load fentry program with rawtp as target_fd
3) create tracing link for fentry program with target_fd = 0
4) repeat 3
In the end we have:
- prog->aux->dst_trampoline == NULL
- tgt_prog == NULL (because we did not provide target_fd to link_create)
- prog->aux->attach_btf == NULL (the program was loaded with attach_prog_fd=X)
- the program was loaded for tgt_prog but we have no way to find out which one
BUG: kernel NULL pointer dereference, address: 0000000000000058
Call Trace:
<TASK>
? __die+0x20/0x70
? page_fault_oops+0x15b/0x430
? fixup_exception+0x22/0x330
? exc_page_fault+0x6f/0x170
? asm_exc_page_fault+0x22/0x30
? bpf_tracing_prog_attach+0x279/0x560
? btf_obj_id+0x5/0x10
bpf_tracing_prog_attach+0x439/0x560
__sys_bpf+0x1cf4/0x2de0
__x64_sys_bpf+0x1c/0x30
do_syscall_64+0x41/0xf0
entry_SYSCALL_64_after_hwframe+0x6e/0x76
Return -EINVAL in this situation.
Signed-off-by: Jiri Olsa <olsajiri@xxxxxxxxx>
Signed-off-by: Dmitrii Dolgov <9erthalion6@xxxxxxxxx>
---
kernel/bpf/syscall.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index c40cad8886e9..5096ddfbe426 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3201,6 +3201,10 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog,
*
* - if prog->aux->dst_trampoline and tgt_prog is NULL, the program
* was detached and is going for re-attachment.
+ *
+ * - if prog->aux->dst_trampoline is NULL and tgt_prog and prog->aux->attach_btf
+ * are NULL, then program was already attached and user did not provide
+ * tgt_prog_fd so we have no way to find out or create trampoline
*/
if (!prog->aux->dst_trampoline && !tgt_prog) {
/*
@@ -3214,6 +3218,11 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog,
err = -EINVAL;
goto out_unlock;
}
+ /* We can allow re-attach only if we have valid attach_btf. */
+ if (!prog->aux->attach_btf) {
+ err = -EINVAL;
+ goto out_unlock;
+ }
btf_id = prog->aux->attach_btf_id;
key = bpf_trampoline_compute_key(NULL, prog->aux->attach_btf, btf_id);
}
--
2.41.0
