v3 addressed Kartikeya's review on v2 and the related Sashiko findings.
v4 fixes the stream_oversize selftest to verify capacity rollback on the
same BPF program stream, since streams live on prog->aux and are not
shared across programs.

Tested locally:
  stream_oversize and stream_partial_read (equivalent to
  ./test_progs -t stream_oversize,stream_partial_read).

Changelog:
v3 -> v4:
  - In stream_oversize, perform the oversized bpf_stream_printk() and a
    subsequent successful "foo" push in the same program; read that
    program's stream in userspace instead of switching to stream_syscall.
  - Drop a redundant vscnprintf() comment in bpf_stream_stage_printk().

v2 -> v3:
  - Refactor bpf_stream_release_capacity() to take a length.
  - Fix staging-path capacity leak; use vscnprintf().
  - Return partial bpf_stream_read() progress on copy_to_user() fault.
  - Reject truncated bpf_stream_vprintk() output with -E2BIG.
  - Add selftests for oversize and straddling-buffer partial read.

v1 -> v2:
  - Retarget to bpf-next as suggested by Pu Lehui.

Links:
v3: https://lore.kernel.org/bpf/?q=%22PATCH+bpf-next+v3+0%2F5%22+fix+stream+capacity
v2: https://lore.kernel.org/bpf/tencent_C919BB32458A4DAD645A68F441345B971E05@qq.com/
v1: https://lore.kernel.org/bpf/tencent_E69EAE29327E25B3548A9AF3F4FA289A6806@qq.com/

Jianlin Shi (5):
  bpf: roll back stream capacity when allocation fails
  bpf: fix stream capacity leak in staging path
  bpf: return partial progress from bpf_stream_read on fault
  bpf: reject oversized bpf_stream_vprintk output with -E2BIG
  selftests/bpf: cover stream capacity and partial read edge cases

 kernel/bpf/stream.c                           | 53 +++++++++------
 .../testing/selftests/bpf/prog_tests/stream.c | 65 +++++++++++++++++++
 tools/testing/selftests/bpf/progs/stream.c    | 18 +++++
 3 files changed, 116 insertions(+), 20 deletions(-)

-- 
2.43.0

On Sun Aug 23, 2026 at 4:17 PM CEST, Jianlin Shi wrote:
> v3 addressed Kartikeya's review on v2 and the related Sashiko findings.
> v4 fixes the stream_oversize selftest to verify capacity rollback on the
> same BPF program stream, since streams live on prog->aux and are not
> shared across programs.
>
> Tested locally:
>   stream_oversize and stream_partial_read (equivalent to
>   ./test_progs -t stream_oversize,stream_partial_read).
>
> Changelog:
> v3 -> v4:
>   - In stream_oversize, perform the oversized bpf_stream_printk() and a
>     subsequent successful "foo" push in the same program; read that
>     program's stream in userspace instead of switching to stream_syscall.
>   - Drop a redundant vscnprintf() comment in bpf_stream_stage_printk().
>
> v2 -> v3:
>   - Refactor bpf_stream_release_capacity() to take a length.
>   - Fix staging-path capacity leak; use vscnprintf().
>   - Return partial bpf_stream_read() progress on copy_to_user() fault.
>   - Reject truncated bpf_stream_vprintk() output with -E2BIG.
>   - Add selftests for oversize and straddling-buffer partial read.
>
> v1 -> v2:
>   - Retarget to bpf-next as suggested by Pu Lehui.
>

Adjusted patch 5 for AI concerns for the selftests and applied. Will post a
separate fix for u32 concern. Thanks!

> Links:
> v3: https://lore.kernel.org/bpf/?q=%22PATCH+bpf-next+v3+0%2F5%22+fix+stream+capacity
> v2: https://lore.kernel.org/bpf/tencent_C919BB32458A4DAD645A68F441345B971E05@qq.com/
> v1: https://lore.kernel.org/bpf/tencent_E69EAE29327E25B3548A9AF3F4FA289A6806@qq.com/
>
> Jianlin Shi (5):
>   bpf: roll back stream capacity when allocation fails
>   bpf: fix stream capacity leak in staging path
>   bpf: return partial progress from bpf_stream_read on fault
>   bpf: reject oversized bpf_stream_vprintk output with -E2BIG
>   selftests/bpf: cover stream capacity and partial read edge cases
>
>  kernel/bpf/stream.c                           | 53 +++++++++------
>  .../testing/selftests/bpf/prog_tests/stream.c | 65 +++++++++++++++++++
>  tools/testing/selftests/bpf/progs/stream.c    | 18 +++++
>  3 files changed, 116 insertions(+), 20 deletions(-)