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Commit eb33f2cc authored by Gianluca Borello's avatar Gianluca Borello Committed by Daniel Borkmann
Browse files

bpf: remove explicit handling of 0 for arg2 in bpf_probe_read 



Commit 9c019e2b ("bpf: change helper bpf_probe_read arg2 type to
ARG_CONST_SIZE_OR_ZERO") changed arg2 type to ARG_CONST_SIZE_OR_ZERO to
simplify writing bpf programs by taking advantage of the new semantics
introduced for ARG_CONST_SIZE_OR_ZERO which allows <!NULL, 0> arguments.

In order to prevent the helper from actually passing a NULL pointer to
probe_kernel_read, which can happen when <NULL, 0> is passed to the helper,
the commit also introduced an explicit check against size == 0.

After the recent introduction of the ARG_PTR_TO_MEM_OR_NULL type,
bpf_probe_read can not receive a pair of <NULL, 0> arguments anymore, thus
the check is not needed anymore and can be removed, since probe_kernel_read
can correctly handle a <!NULL, 0> call. This also fixes the semantics of
the helper before it gets officially released and bpf programs start
relying on this check.

Fixes: 9c019e2b ("bpf: change helper bpf_probe_read arg2 type to ARG_CONST_SIZE_OR_ZERO")
Signed-off-by: default avatarGianluca Borello <g.borello@gmail.com>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent db1ac496

kernel/trace/bpf_trace.c

+1 −5
Original line number Diff line number Diff line
@@ -78,16 +78,12 @@ EXPORT_SYMBOL_GPL(trace_call_bpf); 


BPF_CALL_3(bpf_probe_read, void *, dst, u32, size, const void *, unsafe_ptr)

{

	int ret = 0;



	if (unlikely(size == 0))

		goto out;

	int ret;



	ret = probe_kernel_read(dst, unsafe_ptr, size);

	if (unlikely(ret < 0))

		memset(dst, 0, size);



 out:

	return ret;

}