For now, the reg bounds is not handled for BPF_JNE case, which can cause the failure of following case:
/* The type of "a" is u32 */ if (a > 0 && a < 100) { /* the range of the register for a is [0, 99], not [1, 99], * and will cause the following error: * * invalid zero-sized read * * as a can be 0. */ bpf_skb_store_bytes(skb, xx, xx, a, 0); }
In the code above, "a > 0" will be compiled to "if a == 0 goto xxx". In the TRUE branch, the dst_reg will be marked as known to 0. However, in the fallthrough(FALSE) branch, the dst_reg will not be handled, which makes the [min, max] for a is [0, 99], not [1, 99].
In the 1st patch, we reduce the range of the dst reg if the src reg is a const and is exactly the edge of the dst reg For BPF_JNE.
In the 2nd patch, we remove reduplicated s32 casting in "crafted_cases".
In the 3rd patch, we just activate the test case for this logic in range_cond(), which is committed by Andrii in the commit 8863238993e2 ("selftests/bpf: BPF register range bounds tester").
In the 4th patch, we convert the case above to a testcase and add it to verifier_bounds.c.
Changes since v4: - add the 2nd patch - add "{U32, U32, {0, U32_MAX}, {U32_MAX, U32_MAX}}" that we missed in the 3rd patch - add some comments to the function that we add in the 4th patch - add reg_not_equal_const() in the 4th patch
Changes since v3: - do some adjustment to the crafted cases that we added in the 2nd patch - add the 3rd patch
Changes since v2: - fix a typo in the subject of the 1st patch - add some comments to the 1st patch, as Eduard advised - add some cases to the "crafted_cases"
Changes since v1: - simplify the code in the 1st patch - introduce the 2nd patch for the testing
Menglong Dong (4): bpf: make the verifier tracks the "not equal" for regs selftests/bpf: remove reduplicated s32 casting in "crafted_cases" selftests/bpf: activate the OP_NE logic in range_cond() selftests/bpf: add testcase to verifier_bounds.c for BPF_JNE
kernel/bpf/verifier.c | 38 +++++++++++- .../selftests/bpf/prog_tests/reg_bounds.c | 27 +++++--- .../selftests/bpf/progs/verifier_bounds.c | 62 +++++++++++++++++++ 3 files changed, 116 insertions(+), 11 deletions(-)