[PATCH bpf-next 0/3] Introduce bpf_kern_path and bpf_path_put

[Song Liu]

Security solutions use LSM hook security_sb_mount to monitor mount
operations. security_sb_mount takes dev_name as a string. To get a struct
path from dev_name, in-tree LSMs use kern_path. Introduce kfuncs
bpf_kern_path so that bpf LSM can do similar operations. bpf_kern_path
takes a reference on the return value path. Also add kfunc bpf_path_put to
release path returned by bpf_kern_path. Note that, bpf_kern_path only holds
reference on the path during the duration of this bpf program. The verifier
enforces the bpf program release this reference.

Patch 1/3 prepares bpf verifier to handle const char * passed in as hook
argument. Before this change, bpf helpers and kfuncs only consider value
from read only map as const string.

Patch 2/3 adds the two kfuncs.

Patch 3/3 add tests for the new kfuncs.

Song Liu (3):
  bpf: Allow const char * from LSM hooks as kfunc const string arguments
  bpf: Add bpf_kern_path and bpf_path_put kfuncs
  selftests/bpf: Add tests for bpf_kern_path kfunc

 fs/bpf_fs_kfuncs.c                            | 58 +++++++++++
 include/linux/btf.h                           |  1 +
 kernel/bpf/btf.c                              | 33 +++++++
 kernel/bpf/verifier.c                         | 51 +++++++---
 .../testing/selftests/bpf/bpf_experimental.h  |  4 +
 .../selftests/bpf/prog_tests/kern_path.c      | 82 ++++++++++++++++
 .../selftests/bpf/progs/test_kern_path.c      | 56 +++++++++++
 .../selftests/bpf/progs/verifier_kern_path.c  | 52 ++++++++++
 .../bpf/progs/verifier_kern_path_fail.c       | 97 +++++++++++++++++++
 9 files changed, 422 insertions(+), 12 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/kern_path.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_kern_path.c
 create mode 100644 tools/testing/selftests/bpf/progs/verifier_kern_path.c
 create mode 100644 tools/testing/selftests/bpf/progs/verifier_kern_path_fail.c

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2.47.3