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libbpf: Avoid reading past ELF data section end when copying license

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Fix possible read beyond ELF "license" data section if the license
string is not properly zero-terminated. Use the fact that libbpf_strlcpy
never accesses the (N-1)st byte of the source string because it's
replaced with '\0' anyways.

If this happens, it's a violation of contract between libbpf and a user,
but not handling this more robustly upsets CIFuzz, so given the fix is
trivial, let's fix the potential issue.

Fixes: 9fc205b413 ("libbpf: Add sane strncpy alternative and use it internally")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211214232054.3458774-1-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko 2021-12-14 15:20:54 -08:00 committed by Alexei Starovoitov
parent a34efe503b
commit f97982398c
1 changed files with 4 additions and 1 deletions
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5
tools/lib/bpf/libbpf.c
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@ -1320,7 +1320,10 @@ static int bpf_object__check_endianness(struct bpf_object *obj)
static int
bpf_object__init_license(struct bpf_object *obj, void *data, size_t size)
{
libbpf_strlcpy(obj->license, data, sizeof(obj->license));
/* libbpf_strlcpy() only copies first N - 1 bytes, so size + 1 won't
* go over allowed ELF data section buffer
*/
libbpf_strlcpy(obj->license, data, min(size + 1, sizeof(obj->license)));
pr_debug("license of %s is %s\n", obj->path, obj->license);
return 0;
}