From 3ec3849739a8a52bf18223d9833f6e6b50c6d667 Mon Sep 17 00:00:00 2001
From: Christopher Armstrong <christopherada.a@gmail.com>
Date: Fri, 17 Oct 2025 09:29:56 -0400
Subject: [PATCH 1/2] uucore: add parse_size_non_zero_u64 which fails parsing 0

---
 src/uucore/src/lib/features/parser/parse_size.rs | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/uucore/src/lib/features/parser/parse_size.rs b/src/uucore/src/lib/features/parser/parse_size.rs
index da67a7602..f6f0f1399 100644
--- a/src/uucore/src/lib/features/parser/parse_size.rs
+++ b/src/uucore/src/lib/features/parser/parse_size.rs
@@ -361,6 +361,15 @@ pub fn parse_size_u64(size: &str) -> Result<u64, ParseSizeError> {
     Parser::default().parse_u64(size)
 }
 
+/// Same as `parse_size_u64()`, except 0 fails to parse
+pub fn parse_size_non_zero_u64(size: &str) -> Result<u64, ParseSizeError> {
+    let v = Parser::default().parse_u64(size)?;
+    if v == 0 {
+        return Err(ParseSizeError::ParseFailure("0".to_string()));
+    }
+    Ok(v)
+}
+
 /// Same as `parse_size_u64()` - deprecated
 #[deprecated = "Please use parse_size_u64(size: &str) -> Result<u64, ParseSizeError> OR parse_size_u128(size: &str) -> Result<u128, ParseSizeError> instead."]
 pub fn parse_size(size: &str) -> Result<u64, ParseSizeError> {

From 6015c8fa312610908d0b6c9052e453f9facdc579 Mon Sep 17 00:00:00 2001
From: Christopher Armstrong <christopherada.a@gmail.com>
Date: Fri, 17 Oct 2025 09:32:37 -0400
Subject: [PATCH 2/2] df: treat env var with zero block size as invalid

---
 src/uu/df/src/blocks.rs  |  4 ++--
 tests/by-util/test_df.rs | 28 ++++++++++++++++++++++++++++
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/src/uu/df/src/blocks.rs b/src/uu/df/src/blocks.rs
index d6842f369..ded8b5912 100644
--- a/src/uu/df/src/blocks.rs
+++ b/src/uu/df/src/blocks.rs
@@ -9,7 +9,7 @@ use std::{env, fmt};
 
 use uucore::{
     display::Quotable,
-    parser::parse_size::{ParseSizeError, parse_size_u64},
+    parser::parse_size::{ParseSizeError, parse_size_non_zero_u64, parse_size_u64},
 };
 
 /// The first ten powers of 1024.
@@ -213,7 +213,7 @@ pub(crate) fn read_block_size(matches: &ArgMatches) -> Result<BlockSize, ParseSi
 fn block_size_from_env() -> Option<u64> {
     for env_var in ["DF_BLOCK_SIZE", "BLOCK_SIZE", "BLOCKSIZE"] {
         if let Ok(env_size) = env::var(env_var) {
-            return parse_size_u64(&env_size).ok();
+            return parse_size_non_zero_u64(&env_size).ok();
         }
     }
 
diff --git a/tests/by-util/test_df.rs b/tests/by-util/test_df.rs
index b982e929e..149148699 100644
--- a/tests/by-util/test_df.rs
+++ b/tests/by-util/test_df.rs
@@ -690,6 +690,24 @@ fn test_block_size_from_env() {
     assert_eq!(get_header("BLOCKSIZE", "333"), "333B-blocks");
 }
 
+#[test]
+fn test_block_size_from_env_zero() {
+    fn get_header(env_var: &str, env_value: &str) -> String {
+        let output = new_ucmd!()
+            .arg("--output=size")
+            .env(env_var, env_value)
+            .succeeds()
+            .stdout_str_lossy();
+        output.lines().next().unwrap().trim().to_string()
+    }
+
+    let default_block_size_header = "1K-blocks";
+
+    assert_eq!(get_header("DF_BLOCK_SIZE", "0"), default_block_size_header);
+    assert_eq!(get_header("BLOCK_SIZE", "0"), default_block_size_header);
+    assert_eq!(get_header("BLOCKSIZE", "0"), default_block_size_header);
+}
+
 #[test]
 fn test_block_size_from_env_precedences() {
     fn get_header(one: (&str, &str), two: (&str, &str)) -> String {
@@ -747,6 +765,16 @@ fn test_invalid_block_size_from_env() {
     let header = output.lines().next().unwrap().trim().to_string();
 
     assert_eq!(header, default_block_size_header);
+
+    let output = new_ucmd!()
+        .arg("--output=size")
+        .env("DF_BLOCK_SIZE", "0")
+        .env("BLOCK_SIZE", "222")
+        .succeeds()
+        .stdout_str_lossy();
+    let header = output.lines().next().unwrap().trim().to_string();
+
+    assert_eq!(header, default_block_size_header);
 }
 
 #[test]