[bpf] libbpf: sanitize VAR to conservative 1-byte INT
diff mbox series

Message ID 20190719194603.2704713-1-andriin@fb.com
State Accepted
Delegated to: BPF Maintainers
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Series
  • [bpf] libbpf: sanitize VAR to conservative 1-byte INT
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Commit Message

Andrii Nakryiko July 19, 2019, 7:46 p.m. UTC
If VAR in non-sanitized BTF was size less than 4, converting such VAR
into an INT with size=4 will cause BTF validation failure due to
violationg of STRUCT (into which DATASEC was converted) member size.
Fix by conservatively using size=1.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
 tools/lib/bpf/libbpf.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

Comments

Alexei Starovoitov July 19, 2019, 7:50 p.m. UTC | #1
On 7/19/19 12:46 PM, Andrii Nakryiko wrote:
> If VAR in non-sanitized BTF was size less than 4, converting such VAR
> into an INT with size=4 will cause BTF validation failure due to
> violationg of STRUCT (into which DATASEC was converted) member size.
> Fix by conservatively using size=1.
> 
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>

Applied. Thanks

Patch
diff mbox series

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 87168f21ef43..d8833ff6c4a1 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -1377,8 +1377,13 @@  static void bpf_object__sanitize_btf(struct bpf_object *obj)
 		if (!has_datasec && kind == BTF_KIND_VAR) {
 			/* replace VAR with INT */
 			t->info = BTF_INFO_ENC(BTF_KIND_INT, 0, 0);
-			t->size = sizeof(int);
-			*(int *)(t+1) = BTF_INT_ENC(0, 0, 32);
+			/*
+			 * using size = 1 is the safest choice, 4 will be too
+			 * big and cause kernel BTF validation failure if
+			 * original variable took less than 4 bytes
+			 */
+			t->size = 1;
+			*(int *)(t+1) = BTF_INT_ENC(0, 0, 8);
 		} else if (!has_datasec && kind == BTF_KIND_DATASEC) {
 			/* replace DATASEC with STRUCT */
 			struct btf_var_secinfo *v = (void *)(t + 1);