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Subject[PATCH 4.20 106/183] bpf: dont assume build-id length is always 20 bytes
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4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit 0b698005a9d11c0e91141ec11a2c4918a129f703 ]

Build-id length is not fixed to 20, it can be (`man ld` /--build-id):
* 128-bit (uuid)
* 160-bit (sha1)
* any length specified in ld --build-id=0xhexstring

To fix the issue of missing BPF_STACK_BUILD_ID_VALID for shorter build-ids,
assume that build-id is somewhere in the range of 1 .. 20.
Set the remaining bytes to zero.

v2:
* don't introduce new "len = min(BPF_BUILD_ID_SIZE, nhdr->n_descsz)",
we already know that nhdr->n_descsz <= BPF_BUILD_ID_SIZE if we enter
this 'if' condition

Fixes: 615755a77b24 ("bpf: extend stackmap to save binary_build_id+offset instead of address")
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/bpf/stackmap.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index d9e2483669d0b..f9df545e92f6e 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -180,11 +180,14 @@ static inline int stack_map_parse_build_id(void *page_addr,

if (nhdr->n_type == BPF_BUILD_ID &&
nhdr->n_namesz == sizeof("GNU") &&
- nhdr->n_descsz == BPF_BUILD_ID_SIZE) {
+ nhdr->n_descsz > 0 &&
+ nhdr->n_descsz <= BPF_BUILD_ID_SIZE) {
memcpy(build_id,
note_start + note_offs +
ALIGN(sizeof("GNU"), 4) + sizeof(Elf32_Nhdr),
- BPF_BUILD_ID_SIZE);
+ nhdr->n_descsz);
+ memset(build_id + nhdr->n_descsz, 0,
+ BPF_BUILD_ID_SIZE - nhdr->n_descsz);
return 0;
}
new_offs = note_offs + sizeof(Elf32_Nhdr) +
--
2.19.1


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