From 84d4f24b8c0e2d1dd24b6319ba37ea0fcb90a9e8 Mon Sep 17 00:00:00 2001
From: Jeffrey Finkelstein <jeffrey.finkelstein@protonmail.com>
Date: Fri, 4 Feb 2022 21:42:21 -0500
Subject: [PATCH 1/2] dd: avoid infinite loop in Input::force_fill()

Avoid an infinite loop in `Input::force_fill()` when the input has
fewer bytes than are being requested to be read from the input.
---
 src/uu/dd/src/dd.rs | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/src/uu/dd/src/dd.rs b/src/uu/dd/src/dd.rs
index 54e3190ce..ac7b50d1b 100644
--- a/src/uu/dd/src/dd.rs
+++ b/src/uu/dd/src/dd.rs
@@ -80,8 +80,7 @@ impl Input<io::Stdin> {
         };
 
         if let Some(amt) = skip {
-            let mut buf = vec![BUF_INIT_BYTE; amt];
-            i.force_fill(&mut buf, amt)
+            i.force_fill(amt.try_into().unwrap())
                 .map_err_context(|| "failed to read input".to_string())?;
         }
 
@@ -264,17 +263,19 @@ impl<R: Read> Input<R> {
         })
     }
 
-    /// Force-fills a buffer, ignoring zero-length reads which would otherwise be
-    /// interpreted as EOF.
-    /// Note: This will not return unless the source (eventually) produces
-    /// enough bytes to meet target_len.
-    fn force_fill(&mut self, buf: &mut [u8], target_len: usize) -> std::io::Result<usize> {
-        let mut base_idx = 0;
-        while base_idx < target_len {
-            base_idx += self.read(&mut buf[base_idx..target_len])?;
-        }
-
-        Ok(base_idx)
+    /// Read the specified number of bytes from this reader.
+    ///
+    /// On success, this method returns the number of bytes read. If
+    /// this reader has fewer than `n` bytes available, then it reads
+    /// as many as possible. In that case, this method returns a
+    /// number less than `n`.
+    ///
+    /// # Errors
+    ///
+    /// If there is a problem reading.
+    fn force_fill(&mut self, n: u64) -> std::io::Result<usize> {
+        let mut buf = vec![];
+        self.take(n).read_to_end(&mut buf)
     }
 }
 

From 9f8ec676c53e1f4f4a01d228972601c4e283e0ad Mon Sep 17 00:00:00 2001
From: Jeffrey Finkelstein <jeffrey.finkelstein@protonmail.com>
Date: Fri, 4 Feb 2022 21:44:26 -0500
Subject: [PATCH 2/2] dd: show warning if skipping past end of input

Show a warning if the `skip=N` command-line argument would cause `dd`
to skip past the end of the input. For example:

    $ printf "abcd" | dd bs=1 skip=5 count=0 status=noxfer
    'standard input': cannot skip to specified offset
    0+0 records in
    0+0 records out
---
 src/uu/dd/src/dd.rs      |  7 ++++++-
 tests/by-util/test_dd.rs | 13 +++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/src/uu/dd/src/dd.rs b/src/uu/dd/src/dd.rs
index ac7b50d1b..13bacd946 100644
--- a/src/uu/dd/src/dd.rs
+++ b/src/uu/dd/src/dd.rs
@@ -42,6 +42,7 @@ use gcd::Gcd;
 use signal_hook::consts::signal;
 use uucore::display::Quotable;
 use uucore::error::{FromIo, UResult, USimpleError};
+use uucore::show_error;
 use uucore::InvalidEncodingHandling;
 
 const ABOUT: &str = "copy, and optionally convert, a file system resource";
@@ -80,8 +81,12 @@ impl Input<io::Stdin> {
         };
 
         if let Some(amt) = skip {
-            i.force_fill(amt.try_into().unwrap())
+            let num_bytes_read = i
+                .force_fill(amt.try_into().unwrap())
                 .map_err_context(|| "failed to read input".to_string())?;
+            if num_bytes_read < amt {
+                show_error!("'standard input': cannot skip to specified offset");
+            }
         }
 
         Ok(i)
diff --git a/tests/by-util/test_dd.rs b/tests/by-util/test_dd.rs
index e9a1f9468..30adb05fc 100644
--- a/tests/by-util/test_dd.rs
+++ b/tests/by-util/test_dd.rs
@@ -624,5 +624,18 @@ fn test_seek_bytes() {
         .stdout_is("\0\0\0\0\0\0\0\0abcdefghijklm\n");
 }
 
+/// Test for skipping beyond the number of bytes in a file.
+#[test]
+fn test_skip_beyond_file() {
+    new_ucmd!()
+        .args(&["bs=1", "skip=5", "count=0", "status=noxfer"])
+        .pipe_in("abcd")
+        .succeeds()
+        .no_stdout()
+        .stderr_contains(
+            "'standard input': cannot skip to specified offset\n0+0 records in\n0+0 records out\n",
+        );
+}
+
 // conv=[ascii,ebcdic,ibm], conv=[ucase,lcase], conv=[block,unblock], conv=sync
 // TODO: Move conv tests from unit test module