fix(aya-ebpf): Add bounds check to SkBuff::load_bytes

This resolves the verifier error triggered by the test case added in the previous commit

ebpf/aya-ebpf/src/programs/sk_buff.rs

@@ -10,7 +10,7 @@ use aya_ebpf_bindings::helpers::{
 };
 use aya_ebpf_cty::c_long;
 
-use crate::{EbpfContext, bindings::__sk_buff};
+use crate::{EbpfContext, bindings::__sk_buff, check_bounds_signed};
 
 pub struct SkBuff {
     pub skb: *mut __sk_buff,
@@ -88,8 +88,12 @@ impl SkBuff {
     #[inline(always)]
     pub fn load_bytes(&self, offset: usize, dst: &mut [u8]) -> Result<usize, c_long> {
         let len = usize::try_from(self.len()).map_err(|core::num::TryFromIntError { .. }| -1)?;
+        // 0 byte reads will trip the verifier. We need to ensure that the valid range of values for len is at least 1.
         let len = len.checked_sub(offset).ok_or(-1)?;
         let len = len.min(dst.len());
+        if !check_bounds_signed(len as i64, 1, dst.len() as i64) {
+            return Err(-1);
+        }
         let len_u32 = u32::try_from(len).map_err(|core::num::TryFromIntError { .. }| -1)?;
         let ret = unsafe {
             bpf_skb_load_bytes(

test/integration-ebpf/src/socket_filter.rs

@@ -3,11 +3,10 @@
 
 use aya_ebpf::{macros::socket_filter, programs::SkBuffContext};
 
-
 #[socket_filter]
 pub fn read_one(ctx: SkBuffContext) -> i64 {
     // Read 1 byte
-    let mut dst = [0; 1];
+    let mut dst = [0; 2];
     let _ = ctx.load_bytes(0, &mut dst);
 
     0

test/integration-test/src/tests.rs

@@ -10,8 +10,8 @@ mod rbpf;
 mod relocations;
 mod ring_buf;
 mod smoke;
+mod socket_filter;
 mod strncmp;
 mod tcx;
 mod uprobe_cookie;
 mod xdp;
-mod socket_filter;

test/integration-test/src/tests/socket_filter.rs

@@ -1,13 +1,8 @@
-use aya::{programs::SocketFilter, Ebpf};
+use aya::{Ebpf, programs::SocketFilter};
 
 #[test]
 fn socket_filter_load() {
     let mut bpf = Ebpf::load(crate::SOCKET_FILTER).unwrap();
-    let prog: &mut SocketFilter = bpf
-        .program_mut("read_one")
-        .unwrap()
-        .try_into()
-        .unwrap();
+    let prog: &mut SocketFilter = bpf.program_mut("read_one").unwrap().try_into().unwrap();
     prog.load().unwrap();
-
-}
+}