From 7c81de68b8e13b92cecc5f58ec5dbf759e42f4a9 Mon Sep 17 00:00:00 2001
From: Derick Eddington <124489-kcired@users.noreply.gitlab.redox-os.org>
Date: Sat, 6 Jul 2024 16:52:47 -0700
Subject: [PATCH] Fix `header::grp::parse_grp`.

---
 src/header/grp/mod.rs | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/src/header/grp/mod.rs b/src/header/grp/mod.rs
index 4958791cd9..a91d7e4de7 100644
--- a/src/header/grp/mod.rs
+++ b/src/header/grp/mod.rs
@@ -187,8 +187,8 @@ fn parse_grp(line: String, destbuf: Option<DestBuffer>) -> Result<OwnedGrp, Erro
 
         let members = buffer.next().ok_or(Error::EOF)?;
 
-        // Get the pointer to the members array
-        let member_array_ptr = unsafe { vec.as_mut_ptr().add(vec.len()) as *mut usize };
+        // Get the offset of the members array
+        let member_array_start = vec.len();
 
         // Push enough null pointers to fit all members
         for _member in members
@@ -197,6 +197,7 @@ fn parse_grp(line: String, destbuf: Option<DestBuffer>) -> Result<OwnedGrp, Erro
         {
             vec.extend(0usize.to_ne_bytes());
         }
+        let member_array_end = vec.len();
         // Push a null pointer to terminate the members array
         vec.extend(0usize.to_ne_bytes());
 
@@ -206,10 +207,20 @@ fn parse_grp(line: String, destbuf: Option<DestBuffer>) -> Result<OwnedGrp, Erro
             .filter(|member| !member.is_empty())
             .enumerate()
         {
+            let cur_offset = vec.len();
+
+            // This must be recomputed each time, because `vec` is undergoing extensions and so
+            // its backing memory might be reallocated and moved and its old memory deallocated.
+            let member_array = &mut vec[member_array_start..member_array_end];
+            let member_ptr = {
+                const SIZEOF_PTR: usize = mem::size_of::<*mut c_void>();
+                let start = i * SIZEOF_PTR;
+                let end = start + SIZEOF_PTR;
+                &mut member_array[start..end]
+            };
+
             // Store offset to start of member, MUST BE ADJUSTED LATER BASED ON THE ADDRESS OF THE BUFFER
-            unsafe {
-                *member_array_ptr.add(i) = vec.len();
-            }
+            member_ptr.copy_from_slice(&cur_offset.to_ne_bytes());
 
             vec.extend(member);
             vec.push(0);
@@ -223,7 +234,7 @@ fn parse_grp(line: String, destbuf: Option<DestBuffer>) -> Result<OwnedGrp, Erro
         Some(buf) => {
             let mut buf = MaybeAllocated::Borrowed(buf);
 
-            if buf.len() < buf.len() {
+            if buf.len() < strings.len() {
                 platform::ERRNO.set(errno::ERANGE);
                 return Err(Error::BufTooSmall);
             }