block: qcow: limit max nesting depth for backing file

Impose a limit on the maximum nesting of file formats that can open more
files. For example, a qcow2 file can have a backing file, which could be
another qcow2 file with a backing file (or even the same file as the
original), potentially causing unbounded recursion.

This commit is based on crosvm implementation:
https://chromium.googlesource.com/crosvm/crosvm/+/eb1640e301d66c06e0e0a07886946830f3f2f4fe

Fixes: #6472

Signed-off-by: Yu Li <liyu.yukiteru@bytedance.com>

block/src/lib.rs

@@ -67,6 +67,9 @@ use vmm_sys_util::{ioctl_io_nr, ioctl_ioc_nr};
 const SECTOR_SHIFT: u8 = 9;
 pub const SECTOR_SIZE: u64 = 0x01 << SECTOR_SHIFT;
 
+/// Nesting depth limit for disk formats that can open other disk files.
+pub const MAX_NESTING_DEPTH: u32 = 10;
+
 #[derive(Error, Debug)]
 pub enum Error {
     #[error("Guest gave us bad memory addresses")]
@@ -89,6 +92,8 @@ pub enum Error {
     GetFileMetadata,
     #[error("The requested operation would cause a seek beyond disk end")]
     InvalidOffset,
+    #[error("maximum disk nesting depth exceeded")]
+    MaxNestingDepthExceeded,
     #[error("Failure in qcow: {0}")]
     QcowError(qcow::Error),
     #[error("Failure in raw file: {0}")]
@@ -793,14 +798,23 @@ pub trait BlockBackend: Read + Write + Seek + Send + Debug {
 }
 
 /// Inspect the image file type and create an appropriate disk file to match it.
-pub fn create_disk_file(mut file: File, direct_io: bool) -> Result<Box<dyn BlockBackend>, Error> {
+pub fn create_disk_file(
+    mut file: File,
+    direct_io: bool,
+    mut max_nesting_depth: u32,
+) -> Result<Box<dyn BlockBackend>, Error> {
+    if max_nesting_depth == 0 {
+        return Err(Error::MaxNestingDepthExceeded);
+    }
+    max_nesting_depth -= 1;
+
     let image_type = detect_image_type(&mut file).map_err(Error::DetectImageType)?;
 
     Ok(match image_type {
-        ImageType::Qcow2 => {
-            Box::new(QcowFile::from(RawFile::new(file, direct_io)).map_err(Error::QcowError)?)
-                as Box<dyn BlockBackend>
-        }
+        ImageType::Qcow2 => Box::new(
+            QcowFile::from(RawFile::new(file, direct_io), max_nesting_depth)
+                .map_err(Error::QcowError)?,
+        ) as Box<dyn BlockBackend>,
         ImageType::FixedVhd => {
             Box::new(FixedVhd::new(file).map_err(Error::FixedVhdError)?) as Box<dyn BlockBackend>
         }

block/src/qcow/mod.rs

@@ -414,7 +414,7 @@ fn max_refcount_clusters(refcount_order: u32, cluster_size: u32, num_clusters: u
 /// # use std::io::{Read, Seek, SeekFrom};
 /// # fn test(file: std::fs::File) -> std::io::Result<()> {
 ///     let mut raw_img = RawFile::new(file, false);
-///     let mut q = QcowFile::from(raw_img).expect("Can't open qcow file");
+///     let mut q = QcowFile::from(raw_img, block::MAX_NESTING_DEPTH).expect("Can't open qcow file");
 ///     let mut buf = [0u8; 12];
 ///     q.seek(SeekFrom::Start(10 as u64))?;
 ///     q.read(&mut buf[..])?;
@@ -439,7 +439,7 @@ pub struct QcowFile {
 
 impl QcowFile {
     /// Creates a QcowFile from `file`. File must be a valid qcow2 image.
-    pub fn from(mut file: RawFile) -> Result<QcowFile> {
+    pub fn from(mut file: RawFile, max_nesting_depth: u32) -> Result<QcowFile> {
         let header = QcowHeader::new(&mut file)?;
 
         // Only v2 and v3 files are supported.
@@ -471,8 +471,9 @@ impl QcowFile {
                 .read(true)
                 .open(path)
                 .map_err(Error::BackingFileIo)?;
-            let backing_file = crate::create_disk_file(backing_raw_file, direct_io)
-                .map_err(|e| Error::BackingFileOpen(Box::new(e)))?;
+            let backing_file =
+                crate::create_disk_file(backing_raw_file, direct_io, max_nesting_depth)
+                    .map_err(|e| Error::BackingFileOpen(Box::new(e)))?;
             Some(backing_file)
         } else {
             None
@@ -621,14 +622,16 @@ impl QcowFile {
         file: RawFile,
         version: u32,
         backing_file_name: &str,
+        backing_file_max_nesting_depth: u32,
     ) -> Result<QcowFile> {
         let direct_io = file.is_direct();
         let backing_raw_file = OpenOptions::new()
             .read(true)
             .open(backing_file_name)
             .map_err(Error::BackingFileIo)?;
-        let backing_file = crate::create_disk_file(backing_raw_file, direct_io)
-            .map_err(|e| Error::BackingFileOpen(Box::new(e)))?;
+        let backing_file =
+            crate::create_disk_file(backing_raw_file, direct_io, backing_file_max_nesting_depth)
+                .map_err(|e| Error::BackingFileOpen(Box::new(e)))?;
         let size = backing_file
             .size()
             .map_err(|e| Error::BackingFileOpen(Box::new(e)))?;
@@ -642,7 +645,7 @@ impl QcowFile {
         file.rewind().map_err(Error::SeekingFile)?;
         header.write_to(&mut file)?;
 
-        let mut qcow = Self::from(file)?;
+        let mut qcow = Self::from(file, 1)?;
 
         // Set the refcount for each refcount table cluster.
         let cluster_size = 0x01u64 << qcow.header.cluster_bits;
@@ -1778,11 +1781,16 @@ where
 /// Copy the contents of a disk image in `src_file` into `dst_file`.
 /// The type of `src_file` is automatically detected, and the output file type is
 /// determined by `dst_type`.
-pub fn convert(mut src_file: RawFile, dst_file: RawFile, dst_type: ImageType) -> Result<()> {
+pub fn convert(
+    mut src_file: RawFile,
+    dst_file: RawFile,
+    dst_type: ImageType,
+    src_max_nesting_depth: u32,
+) -> Result<()> {
     let src_type = detect_image_type(&mut src_file)?;
     match src_type {
         ImageType::Qcow2 => {
-            let mut src_reader = QcowFile::from(src_file)?;
+            let mut src_reader = QcowFile::from(src_file, src_max_nesting_depth)?;
             convert_reader(&mut src_reader, dst_file, dst_type)
         }
         ImageType::Raw => {
@@ -1810,6 +1818,8 @@ pub fn detect_image_type(file: &mut RawFile) -> Result<ImageType> {
 
 #[cfg(test)]
 mod tests {
+    use crate::MAX_NESTING_DEPTH;
+
     use super::*;
     use vmm_sys_util::tempfile::TempFile;
     use vmm_sys_util::write_zeroes::WriteZeroes;
@@ -1907,13 +1917,13 @@ mod tests {
     #[test]
     fn write_read_start_backing_v2() {
         let disk_file = basic_file(&valid_header_v2());
-        let mut backing = QcowFile::from(disk_file).unwrap();
+        let mut backing = QcowFile::from(disk_file, MAX_NESTING_DEPTH).unwrap();
         backing
             .write_all(b"test first bytes")
             .expect("Failed to write test string.");
         let mut buf = [0u8; 4];
         let wrapping_disk_file = basic_file(&valid_header_v2());
-        let mut wrapping = QcowFile::from(wrapping_disk_file).unwrap();
+        let mut wrapping = QcowFile::from(wrapping_disk_file, MAX_NESTING_DEPTH).unwrap();
         wrapping.set_backing_file(Some(Box::new(backing)));
         wrapping.seek(SeekFrom::Start(0)).expect("Failed to seek.");
         wrapping.read_exact(&mut buf).expect("Failed to read.");
@@ -1923,13 +1933,13 @@ mod tests {
     #[test]
     fn write_read_start_backing_v3() {
         let disk_file = basic_file(&valid_header_v3());
-        let mut backing = QcowFile::from(disk_file).unwrap();
+        let mut backing = QcowFile::from(disk_file, MAX_NESTING_DEPTH).unwrap();
         backing
             .write_all(b"test first bytes")
             .expect("Failed to write test string.");
         let mut buf = [0u8; 4];
         let wrapping_disk_file = basic_file(&valid_header_v3());
-        let mut wrapping = QcowFile::from(wrapping_disk_file).unwrap();
+        let mut wrapping = QcowFile::from(wrapping_disk_file, MAX_NESTING_DEPTH).unwrap();
         wrapping.set_backing_file(Some(Box::new(backing)));
         wrapping.seek(SeekFrom::Start(0)).expect("Failed to seek.");
         wrapping.read_exact(&mut buf).expect("Failed to read.");
@@ -1945,7 +1955,8 @@ mod tests {
             .write_to(&mut disk_file)
             .expect("Failed to write header to temporary file.");
         disk_file.rewind().unwrap();
-        QcowFile::from(disk_file).expect("Failed to create Qcow from default Header");
+        QcowFile::from(disk_file, MAX_NESTING_DEPTH)
+            .expect("Failed to create Qcow from default Header");
     }
 
     #[test]
@@ -1957,7 +1968,8 @@ mod tests {
             .write_to(&mut disk_file)
             .expect("Failed to write header to temporary file.");
         disk_file.rewind().unwrap();
-        QcowFile::from(disk_file).expect("Failed to create Qcow from default Header");
+        QcowFile::from(disk_file, MAX_NESTING_DEPTH)
+            .expect("Failed to create Qcow from default Header");
     }
 
     #[test]
@@ -2023,7 +2035,8 @@ mod tests {
         let mut header = valid_header_v3();
         header[99] = 2;
         with_basic_file(&header, |disk_file: RawFile| {
-            QcowFile::from(disk_file).expect_err("Invalid refcount order worked.");
+            QcowFile::from(disk_file, MAX_NESTING_DEPTH)
+                .expect_err("Invalid refcount order worked.");
         });
     }
 
@@ -2032,15 +2045,15 @@ mod tests {
         let mut header = valid_header_v3();
         header[23] = 3;
         with_basic_file(&header, |disk_file: RawFile| {
-            QcowFile::from(disk_file).expect_err("Failed to create file.");
+            QcowFile::from(disk_file, MAX_NESTING_DEPTH).expect_err("Failed to create file.");
         });
     }
 
     #[test]
     fn test_header_huge_file() {
         let header = test_huge_header();
         with_basic_file(&header, |disk_file: RawFile| {
-            QcowFile::from(disk_file).expect_err("Failed to create file.");
+            QcowFile::from(disk_file, MAX_NESTING_DEPTH).expect_err("Failed to create file.");
         });
     }
 
@@ -2049,7 +2062,7 @@ mod tests {
         let mut header = valid_header_v3();
         header[24..32].copy_from_slice(&[0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x1e]);
         with_basic_file(&header, |disk_file: RawFile| {
-            QcowFile::from(disk_file).expect_err("Failed to create file.");
+            QcowFile::from(disk_file, MAX_NESTING_DEPTH).expect_err("Failed to create file.");
         });
     }
 
@@ -2058,7 +2071,7 @@ mod tests {
         let mut header = valid_header_v3();
         header[36] = 0x12;
         with_basic_file(&header, |disk_file: RawFile| {
-            QcowFile::from(disk_file).expect_err("Failed to create file.");
+            QcowFile::from(disk_file, MAX_NESTING_DEPTH).expect_err("Failed to create file.");
         });
     }
 
@@ -2070,7 +2083,7 @@ mod tests {
         header[31] = 0;
         // 1 TB with the min cluster size makes the arrays too big, it should fail.
         with_basic_file(&header, |disk_file: RawFile| {
-            QcowFile::from(disk_file).expect_err("Failed to create file.");
+            QcowFile::from(disk_file, MAX_NESTING_DEPTH).expect_err("Failed to create file.");
         });
     }
 
@@ -2084,7 +2097,8 @@ mod tests {
         // set cluster_bits
         header[23] = 16;
         with_basic_file(&header, |disk_file: RawFile| {
-            let mut qcow = QcowFile::from(disk_file).expect("Failed to create file.");
+            let mut qcow =
+                QcowFile::from(disk_file, MAX_NESTING_DEPTH).expect("Failed to create file.");
             qcow.seek(SeekFrom::Start(0x100_0000_0000 - 8))
                 .expect("Failed to seek.");
             let value = 0x0000_0040_3f00_ffffu64;
@@ -2098,7 +2112,8 @@ mod tests {
         let mut header = valid_header_v3();
         header[56..60].copy_from_slice(&[0x02, 0x00, 0xe8, 0xff]);
         with_basic_file(&header, |disk_file: RawFile| {
-            QcowFile::from(disk_file).expect_err("Created disk with crazy refcount clusters");
+            QcowFile::from(disk_file, MAX_NESTING_DEPTH)
+                .expect_err("Created disk with crazy refcount clusters");
         });
     }
 
@@ -2107,14 +2122,15 @@ mod tests {
         let mut header = valid_header_v3();
         header[48..56].copy_from_slice(&[0x00, 0x00, 0x09, 0x00, 0x00, 0x00, 0x02, 0x00]);
         with_basic_file(&header, |disk_file: RawFile| {
-            QcowFile::from(disk_file).expect_err("Created disk with crazy refcount offset");
+            QcowFile::from(disk_file, MAX_NESTING_DEPTH)
+                .expect_err("Created disk with crazy refcount offset");
         });
     }
 
     #[test]
     fn write_read_start() {
         with_basic_file(&valid_header_v3(), |disk_file: RawFile| {
-            let mut q = QcowFile::from(disk_file).unwrap();
+            let mut q = QcowFile::from(disk_file, MAX_NESTING_DEPTH).unwrap();
             q.write_all(b"test first bytes")
                 .expect("Failed to write test string.");
             let mut buf = [0u8; 4];
@@ -2127,12 +2143,12 @@ mod tests {
     #[test]
     fn write_read_start_backing_overlap() {
         let disk_file = basic_file(&valid_header_v3());
-        let mut backing = QcowFile::from(disk_file).unwrap();
+        let mut backing = QcowFile::from(disk_file, MAX_NESTING_DEPTH).unwrap();
         backing
             .write_all(b"test first bytes")
             .expect("Failed to write test string.");
         let wrapping_disk_file = basic_file(&valid_header_v3());
-        let mut wrapping = QcowFile::from(wrapping_disk_file).unwrap();
+        let mut wrapping = QcowFile::from(wrapping_disk_file, MAX_NESTING_DEPTH).unwrap();
         wrapping.set_backing_file(Some(Box::new(backing)));
         wrapping.seek(SeekFrom::Start(0)).expect("Failed to seek.");
         wrapping
@@ -2147,7 +2163,7 @@ mod tests {
     #[test]
     fn offset_write_read() {
         with_basic_file(&valid_header_v3(), |disk_file: RawFile| {
-            let mut q = QcowFile::from(disk_file).unwrap();
+            let mut q = QcowFile::from(disk_file, MAX_NESTING_DEPTH).unwrap();
             let b = [0x55u8; 0x1000];
             q.seek(SeekFrom::Start(0xfff2000)).expect("Failed to seek.");
             q.write_all(&b).expect("Failed to write test string.");
@@ -2161,7 +2177,7 @@ mod tests {
     #[test]
     fn write_zeroes_read() {
         with_basic_file(&valid_header_v3(), |disk_file: RawFile| {
-            let mut q = QcowFile::from(disk_file).unwrap();
+            let mut q = QcowFile::from(disk_file, MAX_NESTING_DEPTH).unwrap();
             // Write some test data.
             let b = [0x55u8; 0x1000];
             q.seek(SeekFrom::Start(0xfff2000)).expect("Failed to seek.");
@@ -2187,7 +2203,7 @@ mod tests {
         // valid_header uses cluster_bits = 12, which corresponds to a cluster size of 4096.
         const CHUNK_SIZE: usize = 4096 * 2 + 512;
         with_basic_file(&valid_header_v3(), |disk_file: RawFile| {
-            let mut q = QcowFile::from(disk_file).unwrap();
+            let mut q = QcowFile::from(disk_file, MAX_NESTING_DEPTH).unwrap();
             // Write some test data.
             let b = [0x55u8; CHUNK_SIZE];
             q.rewind().expect("Failed to seek.");
@@ -2208,19 +2224,19 @@ mod tests {
     #[test]
     fn test_header() {
         with_basic_file(&valid_header_v2(), |disk_file: RawFile| {
-            let q = QcowFile::from(disk_file).unwrap();
+            let q = QcowFile::from(disk_file, MAX_NESTING_DEPTH).unwrap();
             assert_eq!(q.virtual_size(), 0x20_0000_0000);
         });
         with_basic_file(&valid_header_v3(), |disk_file: RawFile| {
-            let q = QcowFile::from(disk_file).unwrap();
+            let q = QcowFile::from(disk_file, MAX_NESTING_DEPTH).unwrap();
             assert_eq!(q.virtual_size(), 0x20_0000_0000);
         });
     }
 
     #[test]
     fn read_small_buffer() {
         with_basic_file(&valid_header_v3(), |disk_file: RawFile| {
-            let mut q = QcowFile::from(disk_file).unwrap();
+            let mut q = QcowFile::from(disk_file, MAX_NESTING_DEPTH).unwrap();
             let mut b = [5u8; 16];
             q.seek(SeekFrom::Start(1000)).expect("Failed to seek.");
             q.read_exact(&mut b).expect("Failed to read.");
@@ -2232,7 +2248,7 @@ mod tests {
     #[test]
     fn replay_ext4() {
         with_basic_file(&valid_header_v3(), |disk_file: RawFile| {
-            let mut q = QcowFile::from(disk_file).unwrap();
+            let mut q = QcowFile::from(disk_file, MAX_NESTING_DEPTH).unwrap();
             const BUF_SIZE: usize = 0x1000;
             let mut b = [0u8; BUF_SIZE];
 

block/src/qcow_sync.rs

@@ -4,7 +4,7 @@
 
 use crate::async_io::{AsyncIo, AsyncIoResult, DiskFile, DiskFileError, DiskFileResult};
 use crate::qcow::{QcowFile, RawFile, Result as QcowResult};
-use crate::AsyncAdaptor;
+use crate::{AsyncAdaptor, MAX_NESTING_DEPTH};
 use std::collections::VecDeque;
 use std::fs::File;
 use std::io::{Seek, SeekFrom};
@@ -18,7 +18,10 @@ pub struct QcowDiskSync {
 impl QcowDiskSync {
     pub fn new(file: File, direct_io: bool) -> QcowResult<Self> {
         Ok(QcowDiskSync {
-            qcow_file: Arc::new(Mutex::new(QcowFile::from(RawFile::new(file, direct_io))?)),
+            qcow_file: Arc::new(Mutex::new(QcowFile::from(
+                RawFile::new(file, direct_io),
+                MAX_NESTING_DEPTH,
+            )?)),
         })
     }
 }