bpf: Fix dynptr ref counting to scan all call frames

Browse source

When checking whether a referenced dynptr can be overwritten,
destroy_if_dynptr_stack_slot only counted sibling dynptrs in the
current call frame. If a clone sharing the same virtual ref parent
existed in a different frame (e.g., passed to a subprog), it would
not be counted, causing the verifier to incorrectly reject the
overwrite with "cannot overwrite referenced dynptr".

Fix by extracting the counting into dynptr_ref_cnt() which uses
bpf_for_each_reg_in_vstate_mask() to scan dynptr stack slots across
all call frames.

Fixes: 017f5c4ef7 ("bpf: Allow overwriting referenced dynptr when refcnt > 1")
Reported-by: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Amery Hung <ameryhung@gmail.com>
Link: https://lore.kernel.org/r/20260529014936.2811085-10-ameryhung@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

...

This commit is contained in:

Amery Hung 2026-05-28 18:49:32 -07:00 • committed by Alexei Starovoitov

parent bcfcb15fde

commit 2eee6fe8ac

1 changed files with 29 additions and 23 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

52

kernel/bpf/verifier.c

View file