[edk2-platforms][PATCH v2 06/11] Ext4Pkg: Add inode number validity check

["Savva Mitrofanov" <savvamtr@gmail.com>]

We need to validate inode number to prevent possible null-pointer
dereference of directory parent in Ext4OpenDirent. Also checks that
inode number valid across opened partition before we read it in
Ext4ReadInode.

Cc: Marvin Häuser <mhaeuser@posteo.de>
Cc: Pedro Falcato <pedro.falcato@gmail.com>
Cc: Vitaly Cheptsov <vit9696@protonmail.com>
Fixes: e55f0527dde48a5f139c1b8f35acc4e6b59dd794
Signed-off-by: Savva Mitrofanov <savvamtr@gmail.com>
---
 Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h   | 15 +++++++++---
 Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h    | 25 ++++++++++++++++++++
 Features/Ext4Pkg/Ext4Dxe/BlockGroup.c |  5 ++++
 Features/Ext4Pkg/Ext4Dxe/Directory.c  | 10 ++++++++
 4 files changed, 52 insertions(+), 3 deletions(-)

diff --git a/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h b/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
index 1285644dcb25..6b56ce6813fc 100644
--- a/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
+++ b/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
@@ -397,7 +397,7 @@ typedef struct _Ext4Inode {
   UINT32       i_projid;
 } EXT4_INODE;
 
-#define EXT4_NAME_MAX 255
+#define EXT4_NAME_MAX  255
 
 typedef struct {
   UINT32    inode;
@@ -469,8 +469,17 @@ typedef UINT64  EXT4_BLOCK_NR;
 typedef UINT32  EXT2_BLOCK_NR;
 typedef UINT32  EXT4_INO_NR;
 
-// 2 is always the root inode number in ext4
-#define EXT4_ROOT_INODE_NR  2
+/* Special inode numbers */
+#define EXT4_ROOT_INODE_NR         2
+#define EXT4_USR_QUOTA_INODE_NR    3
+#define EXT4_GRP_QUOTA_INODE_NR    4
+#define EXT4_BOOT_LOADER_INODE_NR  5
+#define EXT4_UNDEL_DIR_INODE_NR    6
+#define EXT4_RESIZE_INODE_NR       7
+#define EXT4_JOURNAL_INODE_NR      8
+
+/* First non-reserved inode for old ext4 filesystems */
+#define EXT4_GOOD_OLD_FIRST_INODE_NR  11
 
 #define EXT4_BLOCK_FILE_HOLE  0
 
diff --git a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
index 81ba568c5947..beceb9d60dcb 100644
--- a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
+++ b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
@@ -287,6 +287,31 @@ Ext4GetBlockGroupDesc (
   IN UINT32          BlockGroup
   );
 
+/**
+   Retrieves the first usable non-reserved inode number from the superblock
+   of the opened partition.
+
+   @param[in]  Partition      Pointer to the opened ext4 partition.
+
+   @return The first usable inode number (non-reserved).
+**/
+#define EXT4_FIRST_INODE_NR(Partition)                                         \
+  ((Partition->SuperBlock.s_rev_level == EXT4_GOOD_OLD_REV) ?                  \
+         EXT4_GOOD_OLD_FIRST_INODE_NR :                                        \
+         Partition->SuperBlock.s_first_ino)
+
+/**
+   Checks inode number validity across superblock of the opened partition.
+
+   @param[in]  Partition      Pointer to the opened ext4 partition.
+
+   @return TRUE if inode number is valid.
+**/
+#define EXT4_IS_VALID_INODE_NR(Partition, InodeNum)                            \
+  (InodeNum == EXT4_ROOT_INODE_NR ||                                           \
+        (InodeNum >= EXT4_FIRST_INODE_NR(Partition) &&                         \
+         InodeNum <= Partition->SuperBlock.s_inodes_count))
+
 /**
    Reads an inode from disk.
 
diff --git a/Features/Ext4Pkg/Ext4Dxe/BlockGroup.c b/Features/Ext4Pkg/Ext4Dxe/BlockGroup.c
index cba96cd95afc..f34cdc5dbad7 100644
--- a/Features/Ext4Pkg/Ext4Dxe/BlockGroup.c
+++ b/Features/Ext4Pkg/Ext4Dxe/BlockGroup.c
@@ -50,6 +50,11 @@ Ext4ReadInode (
   EXT4_BLOCK_NR          InodeTableStart;
   EFI_STATUS             Status;
 
+  if (!EXT4_IS_VALID_INODE_NR (Partition, InodeNum)) {
+    DEBUG ((DEBUG_ERROR, "[ext4] Error reading inode: inode number %lu isn't valid\n", InodeNum));
+    return EFI_VOLUME_CORRUPTED;
+  }
+
   BlockGroupNumber = (UINT32)DivU64x64Remainder (
                                InodeNum - 1,
                                Partition->SuperBlock.s_inodes_per_group,
diff --git a/Features/Ext4Pkg/Ext4Dxe/Directory.c b/Features/Ext4Pkg/Ext4Dxe/Directory.c
index ffc0e8043076..ff476c8641e8 100644
--- a/Features/Ext4Pkg/Ext4Dxe/Directory.c
+++ b/Features/Ext4Pkg/Ext4Dxe/Directory.c
@@ -163,6 +163,10 @@ Ext4RetrieveDirent (
       if (Entry->inode == 0) {
         BlockOffset += Entry->rec_len;
         continue;
+      } else if (!EXT4_IS_VALID_INODE_NR (Partition, Entry->inode)) {
+        DEBUG ((DEBUG_ERROR, "[ext4] Ext4RetrieveDirent directory entry inode number %u isn't valid\n", Entry->inode));
+        Status = EFI_VOLUME_CORRUPTED;
+        goto Out;
       }
 
       Status = Ext4GetUcs2DirentName (Entry, DirentUcs2Name);
@@ -498,6 +502,12 @@ Ext4ReadDir (
     // When inode = 0, it's unused.
     ShouldSkip = Entry.inode == 0 || IsDotOrDotDot;
 
+    if ((Entry.inode != 0) && !EXT4_IS_VALID_INODE_NR (Partition, Entry.inode)) {
+      DEBUG ((DEBUG_ERROR, "[ext4] Ext4ReadDir directory entry inode number %u isn't valid\n", Entry.inode));
+      Status = EFI_VOLUME_CORRUPTED;
+      goto Out;
+    }
+
     if (ShouldSkip) {
       Offset += Entry.rec_len;
       continue;
-- 
2.38.1