Merge pull request #721 from ReFirmLabs/apfs_support

Apfs support

dependencies/src.sh

@@ -39,3 +39,12 @@ make
 cp srec2bin /usr/local/bin/
 cd /tmp
 rm -rf /tmp/srec
+
+# Install latest version of 7z (static) for APFS support
+mkdir /tmp/7z
+cd /tmp/7z
+wget https://www.7-zip.org/a/7z2408-linux-x64.tar.xz
+tar -xf 7z2408-linux-x64.tar.xz
+cp 7zzs /usr/local/bin/
+cd /tmp
+rm -rf /tmp/7z

src/binwalk.rs

@@ -277,8 +277,8 @@ impl Binwalk {
                             signature_result.name, FILE_START_OFFSET
                         );
 
-                        // Only update the next_valid_offset if confidence is at least medium
-                        if signature_result.confidence >= signatures::common::CONFIDENCE_MEDIUM {
+                        // Only update the next_valid_offset if confidence is high; these are, after all, short signatures
+                        if signature_result.confidence >= signatures::common::CONFIDENCE_HIGH {
                             next_valid_offset = signature_result.offset + signature_result.size;
                         }
 

src/extractors.rs

@@ -140,6 +140,7 @@
 //! ```
 
 pub mod androidsparse;
+pub mod apfs;
 pub mod arcadyan;
 pub mod autel;
 pub mod bzip2;

src/extractors/apfs.rs

@@ -0,0 +1,18 @@
+use crate::extractors;
+
+/// Describes how to run the 7zzs utility to extract APFS images
+pub fn apfs_extractor() -> extractors::common::Extractor {
+    extractors::common::Extractor {
+        utility: extractors::common::ExtractorType::External("7zzs".to_string()),
+        extension: "img".to_string(),
+        arguments: vec![
+            "x".to_string(),   // Perform extraction
+            "-y".to_string(),  // Assume Yes to all questions
+            "-o.".to_string(), // Output to current working directory
+            extractors::common::SOURCE_FILE_PLACEHOLDER.to_string(),
+        ],
+        // If there is trailing data after the compressed data, extraction will happen but exit code will be 2
+        exit_codes: vec![0, 2],
+        ..Default::default()
+    }
+}

src/magic.rs

@@ -910,6 +910,17 @@ pub fn patterns() -> Vec<signatures::common::Signature> {
             description: signatures::ntfs::DESCRIPTION.to_string(),
             extractor: Some(extractors::tsk::tsk_extractor()),
         },
+        // APFS
+        signatures::common::Signature {
+            name: "apfs".to_string(),
+            short: false,
+            magic_offset: 0,
+            always_display: false,
+            magic: signatures::apfs::apfs_magic(),
+            parser: signatures::apfs::apfs_parser,
+            description: signatures::apfs::DESCRIPTION.to_string(),
+            extractor: Some(extractors::apfs::apfs_extractor()),
+        },
     ];
 
     binary_signatures

src/signatures.rs

@@ -107,6 +107,7 @@
 //! ```
 pub mod aes;
 pub mod androidsparse;
+pub mod apfs;
 pub mod arcadyan;
 pub mod autel;
 pub mod binhdr;

src/signatures/apfs.rs

@@ -0,0 +1,56 @@
+use crate::signatures::common::{SignatureError, SignatureResult, CONFIDENCE_MEDIUM};
+use crate::structures::apfs::{parse_apfs_header, MAGIC_OFFSET};
+
+/// Human readable description
+pub const DESCRIPTION: &str = "APple File System";
+
+/// APFS magic bytes
+pub fn apfs_magic() -> Vec<Vec<u8>> {
+    vec![b"NXSB".to_vec()]
+}
+
+/// Validates the APFS header
+pub fn apfs_parser(file_data: &[u8], offset: usize) -> Result<SignatureResult, SignatureError> {
+    const MBR_BLOCK_SIZE: usize = 512;
+
+    // Successful return value
+    let mut result = SignatureResult {
+        description: DESCRIPTION.to_string(),
+        confidence: CONFIDENCE_MEDIUM,
+        ..Default::default()
+    };
+
+    if offset >= MAGIC_OFFSET {
+        result.offset = offset - MAGIC_OFFSET;
+        let available_data = file_data.len() - result.offset;
+
+        if let Ok(apfs_header) = parse_apfs_header(&file_data[result.offset..]) {
+            let mut truncated_message = "".to_string();
+            result.size = apfs_header.block_count * apfs_header.block_size;
+
+            // It is observed that an APFS contained in an EFIGPT with a protective MBR includes the MBR block in its size.
+            // If the APFS image is pulled out of the EFIGPT, the reported size will be 512 bytes too long, but otherwise valid.
+            if result.size > available_data {
+                let truncated_size = result.size - available_data;
+
+                // If the calculated size is 512 bytes short, adjust the reported APFS size accordingly
+                if truncated_size == MBR_BLOCK_SIZE {
+                    result.size -= truncated_size;
+                    truncated_message = format!(" (truncated by {} bytes)", truncated_size);
+                }
+            }
+
+            result.description = format!(
+                "{}, block size: {} bytes, block count: {}, total size: {} bytes{}",
+                result.description,
+                apfs_header.block_size,
+                apfs_header.block_count,
+                result.size,
+                truncated_message
+            );
+            return Ok(result);
+        }
+    }
+
+    Err(SignatureError)
+}

src/structures.rs

@@ -97,6 +97,7 @@
 //! ```
 
 pub mod androidsparse;
+pub mod apfs;
 pub mod autel;
 pub mod binhdr;
 pub mod cab;

src/structures/apfs.rs

@@ -0,0 +1,87 @@
+use crate::structures::common::{self, StructureError};
+
+/// Offset of the APFS magic bytes from the start of the APFS image
+pub const MAGIC_OFFSET: usize = 0x20;
+
+/// Struct to store APFS header info
+#[derive(Debug, Default, Clone)]
+pub struct APFSHeader {
+    pub block_size: usize,
+    pub block_count: usize,
+}
+
+/// Parses an APFS header
+pub fn parse_apfs_header(apfs_data: &[u8]) -> Result<APFSHeader, StructureError> {
+    const MAX_FS_COUNT: usize = 100;
+    const FS_COUNT_BLOCK_SIZE: usize = 512;
+
+    // Partial APFS header, just to figure out the size of the image and validate some fields
+    // https://developer.apple.com/support/downloads/Apple-File-System-Reference.pdf
+    let apfs_structure = vec![
+        ("magic", "u32"),
+        ("block_size", "u32"),
+        ("block_count", "u64"),
+        ("nx_features", "u64"),
+        ("nx_ro_compat_features", "u64"),
+        ("nx_incompat_features", "u64"),
+        ("nx_uuid_p1", "u64"),
+        ("nx_uuid_p2", "u64"),
+        ("nx_next_oid", "u64"),
+        ("nx_next_xid", "u64"),
+        ("nx_xp_desc_blocks", "u32"),
+        ("nx_xp_data_blocks", "u32"),
+        ("nx_xp_desc_base", "u64"),
+        ("nx_xp_data_base", "u64"),
+        ("nx_xp_desc_next", "u32"),
+        ("nx_xp_data_next", "u32"),
+        ("nx_xp_desc_index", "u32"),
+        ("nx_xp_desc_len", "u32"),
+        ("nx_xp_data_index", "u32"),
+        ("nx_xp_data_len", "u32"),
+        ("nx_spaceman_oid", "u64"),
+        ("nx_omap_oid", "u64"),
+        ("nx_reaper_oid", "u64"),
+        ("nx_xp_test_type", "u32"),
+        ("nx_xp_max_file_systems", "u32"),
+    ];
+
+    // Expected values of superblock flag fields
+    let allowed_feature_flags: Vec<usize> = vec![0, 1, 2, 3];
+    let allowed_incompat_flags: Vec<usize> = vec![0, 1, 2, 3, 0x100, 0x101, 0x102, 0x103];
+    let allowed_ro_compat_flags: Vec<usize> = vec![0];
+
+    let apfs_struct_start = MAGIC_OFFSET;
+    let apfs_struct_end = apfs_struct_start + common::size(&apfs_structure);
+
+    // Parse the header
+    if let Some(apfs_structure_data) = apfs_data.get(apfs_struct_start..apfs_struct_end) {
+        if let Ok(apfs_header) = common::parse(apfs_structure_data, &apfs_structure, "little") {
+            // Simple sanity check on the reported block data
+            if apfs_header["block_size"] != 0 && apfs_header["block_count"] != 0 {
+                // Sanity check the feature flags
+                if allowed_feature_flags.contains(&apfs_header["nx_features"])
+                    && allowed_ro_compat_flags.contains(&apfs_header["nx_ro_compat_features"])
+                    && allowed_incompat_flags.contains(&apfs_header["nx_incompat_features"])
+                {
+                    // The test_type field *must* be NULL
+                    if apfs_header["nx_xp_test_type"] == 0 {
+                        // Calculate the file system count; this is max_file_systems divided by 512, rounded up to nearest whole
+                        let fs_count = ((apfs_header["nx_xp_max_file_systems"] as f32)
+                            / (FS_COUNT_BLOCK_SIZE as f32))
+                            .ceil() as usize;
+
+                        // Sanity check the file system count
+                        if fs_count > 0 && fs_count <= MAX_FS_COUNT {
+                            return Ok(APFSHeader {
+                                block_size: apfs_header["block_size"],
+                                block_count: apfs_header["block_count"],
+                            });
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    Err(StructureError)
+}