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.
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
lib/strncpy_from_user.c | 8 ++-
.../bpf/prog_tests/probe_read_user_str.c | 71 +++++++++++++++++++
.../bpf/progs/test_probe_read_user_str.c | 25 +++++++
3 files changed, 102 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
--
2.29.2
