From 2ac433449cdea32f10c8fc88218799995946032d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alessandro=C2=A0Decina?= <alessandro.d@gmail.com>
Date: Fri, 15 Oct 2021 08:13:18 +0000
Subject: [PATCH] Minor tweaks to make the verifier's job easier

---
 aya-log/aya-log-ebpf/src/lib.rs    | 11 +++++++++--
 aya-log/aya-log-ebpf/src/macros.rs |  5 ++++-
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/aya-log/aya-log-ebpf/src/lib.rs b/aya-log/aya-log-ebpf/src/lib.rs
index 448f0871..56ae6746 100644
--- a/aya-log/aya-log-ebpf/src/lib.rs
+++ b/aya-log/aya-log-ebpf/src/lib.rs
@@ -11,7 +11,8 @@ use aya_bpf::{
     maps::{PerCpuArray, PerfEventByteArray},
 };
 pub use aya_log_common::Level;
-use aya_log_common::{RecordField, LOG_BUF_CAPACITY};
+use aya_log_common::RecordField;
+pub use aya_log_common::LOG_BUF_CAPACITY;
 
 #[doc(hidden)]
 #[repr(C)]
@@ -59,12 +60,18 @@ impl<'a> ufmt::uWrite for LogBufWriter<'a> {
     fn write_str(&mut self, s: &str) -> Result<(), Self::Error> {
         let bytes = s.as_bytes();
         let len = bytes.len();
+
+        // this is to make sure the verifier knows about the upper bound
+        if len > LOG_BUF_CAPACITY {
+            return Err(());
+        }
+
         let available = self.data.len() - self.pos;
         if available < len {
             return Err(());
         }
 
-        self.data[self.pos..self.pos + len].copy_from_slice(bytes);
+        self.data[self.pos..self.pos + len].copy_from_slice(&bytes[..len]);
         self.pos += len;
         Ok(())
     }
diff --git a/aya-log/aya-log-ebpf/src/macros.rs b/aya-log/aya-log-ebpf/src/macros.rs
index f4c420f1..2d2ee666 100644
--- a/aya-log/aya-log-ebpf/src/macros.rs
+++ b/aya-log/aya-log-ebpf/src/macros.rs
@@ -183,7 +183,10 @@ macro_rules! log {
         if let Some(buf) = unsafe { $crate::AYA_LOG_BUF.get_mut(0) } {
             if let Ok(header_len) = $crate::write_record_header(&mut buf.buf, module_path!(), $lvl, module_path!(), file!(), line!()) {
                 if let Ok(message_len) = $crate::write_record_message!(&mut buf.buf[header_len..], $($arg)+) {
-                    let _ = unsafe { $crate::AYA_LOGS.output($ctx, &buf.buf[..header_len + message_len], 0) };
+                    let record_len = header_len + message_len;
+                    if record_len <= $crate::LOG_BUF_CAPACITY {
+                        let _ = unsafe { $crate::AYA_LOGS.output($ctx, &buf.buf[..header_len + message_len], 0) };
+                    }
                 };
             }
         }