Add discriminator length checks instead of panicking in `(Account)Loader` (#1678)

CHANGELOG.md

@@ -17,6 +17,7 @@ The minor version will be incremented upon a breaking change and the patch versi
 ### Fixes
 
 * avm: `avm install` no longer downloads the version if already installed in the machine ([#1670](https://github.com/project-serum/anchor/pull/1670)).
+* lang: Return proper error instead of panicking if account length is smaller than discriminator in functions of `(Account)Loader` ([#1678](https://github.com/project-serum/anchor/pull/1678)).
 
 ### Breaking
 

lang/src/accounts/account_loader.rs

@@ -124,6 +124,9 @@ impl<'info, T: ZeroCopy + Owner> AccountLoader<'info, T> {
                 .with_pubkeys((*acc_info.owner, T::owner())));
         }
         let data: &[u8] = &acc_info.try_borrow_data()?;
+        if data.len() < T::discriminator().len() {
+            return Err(ErrorCode::AccountDiscriminatorNotFound.into());
+        }
         // Discriminator must match.
         let disc_bytes = array_ref![data, 0, 8];
         if disc_bytes != &T::discriminator() {
@@ -149,6 +152,9 @@ impl<'info, T: ZeroCopy + Owner> AccountLoader<'info, T> {
     /// Returns a Ref to the account data structure for reading.
     pub fn load(&self) -> Result<Ref<T>> {
         let data = self.acc_info.try_borrow_data()?;
+        if data.len() < T::discriminator().len() {
+            return Err(ErrorCode::AccountDiscriminatorNotFound.into());
+        }
 
         let disc_bytes = array_ref![data, 0, 8];
         if disc_bytes != &T::discriminator() {
@@ -169,6 +175,9 @@ impl<'info, T: ZeroCopy + Owner> AccountLoader<'info, T> {
         }
 
         let data = self.acc_info.try_borrow_mut_data()?;
+        if data.len() < T::discriminator().len() {
+            return Err(ErrorCode::AccountDiscriminatorNotFound.into());
+        }
 
         let disc_bytes = array_ref![data, 0, 8];
         if disc_bytes != &T::discriminator() {

lang/src/accounts/loader.rs

@@ -63,6 +63,9 @@ impl<'info, T: ZeroCopy> Loader<'info, T> {
                 .with_pubkeys((*acc_info.owner, *program_id)));
         }
         let data: &[u8] = &acc_info.try_borrow_data()?;
+        if data.len() < T::discriminator().len() {
+            return Err(ErrorCode::AccountDiscriminatorNotFound.into());
+        }
         // Discriminator must match.
         let disc_bytes = array_ref![data, 0, 8];
         if disc_bytes != &T::discriminator() {
@@ -90,6 +93,9 @@ impl<'info, T: ZeroCopy> Loader<'info, T> {
     #[allow(deprecated)]
     pub fn load(&self) -> Result<Ref<T>> {
         let data = self.acc_info.try_borrow_data()?;
+        if data.len() < T::discriminator().len() {
+            return Err(ErrorCode::AccountDiscriminatorNotFound.into());
+        }
 
         let disc_bytes = array_ref![data, 0, 8];
         if disc_bytes != &T::discriminator() {
@@ -109,6 +115,9 @@ impl<'info, T: ZeroCopy> Loader<'info, T> {
         }
 
         let data = self.acc_info.try_borrow_mut_data()?;
+        if data.len() < T::discriminator().len() {
+            return Err(ErrorCode::AccountDiscriminatorNotFound.into());
+        }
 
         let disc_bytes = array_ref![data, 0, 8];
         if disc_bytes != &T::discriminator() {