[PATCH bpf v7 0/2] Fix bpf_probe_read_user_str() overcopying

From: Daniel Xu
Date: Tue Nov 17 2020 - 15:06:04 EST


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.

v6 -> v7:
* Add comments

v5 -> v6:
* zero-pad up to sizeof(unsigned long) after NUL

v4 -> v5:
* don't read potentially uninitialized memory

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

kernel/trace/bpf_trace.c | 10 +++
lib/strncpy_from_user.c | 19 ++++-
.../bpf/prog_tests/probe_read_user_str.c | 71 +++++++++++++++++++
.../bpf/progs/test_probe_read_user_str.c | 25 +++++++
4 files changed, 123 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

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2.29.2