From 4846d21ff9d0a77190c4468413cace07f2b40714 Mon Sep 17 00:00:00 2001
From: Ron Williams <ron.williams.redox@gmail.com>
Date: Fri, 28 Jul 2023 01:50:39 -0700
Subject: [PATCH] block-io-wrapper: allow up to MAX offset + len

---
 block-io-wrapper/src/lib.rs | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/block-io-wrapper/src/lib.rs b/block-io-wrapper/src/lib.rs
index 278c88cc54..ced957f2a6 100644
--- a/block-io-wrapper/src/lib.rs
+++ b/block-io-wrapper/src/lib.rs
@@ -18,11 +18,13 @@ pub fn read(
     if buf.len() == 0 {
         return Ok(0);
     }
-    let _ = offset.checked_add(buf.len() as u64).ok_or(Error::new(
-        ErrorKind::InvalidInput,
-        "Offset + Length greater than 2^64",
-    ))?;
-    let mut curr_buf = buf;
+    let (_, would_overflow) = offset.overflowing_add(buf.len() as u64);
+    let to_copy = if would_overflow {
+        usize::try_from(u64::MAX - offset).map_err(|_| Error::new(ErrorKind::Unsupported, "offset + len exceeds usize::MAX"))?
+    } else {
+        buf.len()
+    };
+    let mut curr_buf = &mut buf[..to_copy];
     let mut curr_offset = offset;
     let blk_size = usize::try_from(blksize).expect("blksize larger than usize");
     let mut total_read = 0;