On Sat, May 4, 2024 at 6:49 PM Camila Alvarez <cam.alvarez.i@xxxxxxxxx> wrote:
The error indicates that the verifier is letting through a program with
a stack depth bigger than 512.
This is due to the verifier not checking the stack depth after
instruction rewrites are perfomed. For example, the MAY_GOTO instruction
adds 8 bytes to the stack, which means that if the stack at the moment
was already 512 bytes it would overflow after rewriting the instruction.
This is by design. may_goto and other constructs like bpf_loop
inlining can consume a few words above 512 limit.
The fix involves adding a stack depth check after all instruction
rewrites are performed.
Reported-by: syzbot+d2a2c639d03ac200a4f1@xxxxxxxxxxxxxxxxxxxxxxxxx
This syzbot report is likely unrelated.
It says that it bisected it to may_goto, but it has this report
before may_goto was introduced, so bisection is incorrect.
pw-bot: cr
Signed-off-by: Camila Alvarez <cam.alvarez.i@xxxxxxxxx>
---
kernel/bpf/verifier.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 63749ad5ac6b..a9e23b6b8e8f 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -21285,6 +21285,10 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u3
if (ret == 0)
ret = do_misc_fixups(env);
+ /* max stack depth verification must be done after rewrites as well */
+ if (ret == 0)
+ ret = check_max_stack_depth(env);
+
/* do 32-bit optimization after insn patching has done so those patched
* insns could be handled correctly.
*/
--
2.34.1