If the account length is zero, no data region is present (#5122)

This only affects unaligned programs, as for aligned programs the resize
area address will match the account region address if the data length is
zero.

(cherry picked from commit 561023d)

programs/bpf_loader/src/syscalls/mem_ops.rs

@@ -532,7 +532,7 @@ impl<'a> Iterator for MemoryChunkIterator<'a> {
                     account_index = account_index.saturating_add(1);
                     self.account_index = Some(account_index);
                 } else {
-                    region_is_account = region.vm_addr == account_addr
+                    region_is_account = (account.original_data_len != 0 && region.vm_addr == account_addr)
                         // unaligned programs do not have a resize area
                         || (self.resize_area && region.vm_addr == resize_addr);
                     break;
@@ -606,7 +606,7 @@ impl DoubleEndedIterator for MemoryChunkIterator<'_> {
 
                 self.account_index = Some(account_index);
             } else {
-                region_is_account = region.vm_addr == account_addr
+                region_is_account = (account.original_data_len != 0 && region.vm_addr == account_addr)
                     // unaligned programs do not have a resize area
                     || (self.resize_area && region.vm_addr == resize_addr);
                 break;

programs/sbf/rust/account_mem/src/lib.rs

@@ -60,8 +60,15 @@ pub fn process_instruction(
             sol_memset(&mut data[data_len.saturating_sub(2)..], 0, 3);
         }
         5 => {
+            // memcmp overlaps begining
+            #[allow(clippy::manual_memcpy)]
+            for i in 0..3 {
+                buf[i] = too_early(2)[i];
+            }
+
             // memset overlaps begin of account area
             sol_memset(too_early(2), 3, 3);
+            sol_memcpy(too_early(2), &buf, 3);
         }
         6 => {
             // memcpy src overlaps end of account

programs/sbf/rust/account_mem_deprecated/src/lib.rs

@@ -25,7 +25,7 @@ pub fn process_instruction(
     let mut too_early = |before: usize| -> &mut [u8] {
         let data = data.as_mut_ptr().wrapping_sub(before);
 
-        unsafe { std::slice::from_raw_parts_mut(data, data_len) }
+        unsafe { std::slice::from_raw_parts_mut(data, data_len.wrapping_add(100)) }
     };
 
     match instruction_data[0] {
@@ -40,11 +40,11 @@ pub fn process_instruction(
         2 => {
             // memcmp overlaps begining
             #[allow(clippy::manual_memcpy)]
-            for i in 0..500 {
+            for i in 0..90 {
                 buf[i] = too_early(8)[i];
             }
 
-            sol_memcmp(too_early(8), &buf, 500);
+            sol_memcmp(too_early(8), &buf, 90);
         }
         3 => {
             // memcmp overlaps begining

programs/sbf/tests/programs.rs

@@ -5194,6 +5194,29 @@ fn test_mem_syscalls_overlap_account_begin_or_end() {
                     assert!(!logs.last().unwrap().ends_with(" failed: InvalidLength"));
                 }
             }
+
+            let account = AccountSharedData::new(42, 0, &program_id);
+            bank.store_account(&account_keypair.pubkey(), &account);
+
+            for instr in 0..=15 {
+                println!("Testing deprecated:{deprecated} direct_mapping:{direct_mapping} instruction:{instr} zero-length account");
+                let instruction =
+                    Instruction::new_with_bytes(program_id, &[instr, 0], account_metas.clone());
+
+                let message = Message::new(&[instruction], Some(&mint_pubkey));
+                let tx = Transaction::new(&[&mint_keypair], message.clone(), bank.last_blockhash());
+                let (result, _, logs, _) = process_transaction_and_record_inner(&bank, tx);
+
+                if direct_mapping && !deprecated {
+                    // we have a resize area
+                    assert!(
+                        logs.last().unwrap().ends_with(" failed: InvalidLength"),
+                        "{logs:?}"
+                    );
+                } else {
+                    assert!(result.is_ok(), "{logs:?}");
+                }
+            }
         }
     }
 }