From: Stanislav Fomichev <sdf@google.com>
Date: Wed, 16 Jan 2019 14:03:15 -0800
Subject: bpf: don't assume build-id length is always 20 bytes
Patch-mainline: v5.0-rc3
Git-commit: 0b698005a9d11c0e91141ec11a2c4918a129f703
References: bsc#1109837

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>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 kernel/bpf/stackmap.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -180,11 +180,14 @@ static inline int stack_map_parse_build_
 
 		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) +