linux-kernel - [PATCH bpf v4 0/2] Fix bpf_probe_read_user

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Date:   Thu,  5 Nov 2020 16:06:33 -0800
From:   Daniel Xu <dxu@...uu.xyz>
To:     bpf@...r.kernel.org, linux-kernel@...r.kernel.org, ast@...nel.org,
        daniel@...earbox.net, songliubraving@...com,
        andrii.nakryiko@...il.com
Cc:     Daniel Xu <dxu@...uu.xyz>, kernel-team@...com
Subject: [PATCH bpf v4 0/2] Fix bpf_probe_read_user_str() overcopying

6ae08ae3dea2 ("bpf: Add probe_read_{user, kernel} and probe_read_{user,
kernel}_str helpers") introduced a subtle bug where
bpf_probe_read_user_str() would potentially copy a few extra bytes after
the NUL terminator.

This issue is particularly nefarious when strings are used as map keys,
as seemingly identical strings can occupy multiple entries in a map.

This patchset fixes the issue and introduces a selftest to prevent
future regressions.

v3 -> v4:
* directly pass userspace pointer to prog
* test more strings of different length

v2 -> v3:
* set pid filter before attaching prog in selftest
* use long instead of int as bpf_probe_read_user_str() retval
* style changes

v1 -> v2:
* add Fixes: tag
* add selftest

Daniel Xu (2):
  lib/strncpy_from_user.c: Don't overcopy bytes after NUL terminator
  selftest/bpf: Test bpf_probe_read_user_str() strips trailing bytes
    after NUL

 lib/strncpy_from_user.c                       |  9 ++-
 .../bpf/prog_tests/probe_read_user_str.c      | 71 +++++++++++++++++++
 .../bpf/progs/test_probe_read_user_str.c      | 25 +++++++
 3 files changed, 103 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/probe_read_user_str.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_probe_read_user_str.c

-- 
2.28.0