Skip to content

Fix virtio-fs escape outside of root directory (on Linux) #330

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Draft
wants to merge 2 commits into
base: main
Choose a base branch
from
Draft

Fix virtio-fs escape outside of root directory (on Linux) #330

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
3882926
fs: Verify filenames don't contain '/'
mtjhrc May 12, 2025
da406a5
fs: [Linux] Don't allow the guest to resolve '..' of '/'
mtjhrc May 12, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
25 changes: 25 additions & 0 deletions src/devices/src/virtio/fs/linux/passthrough.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -352,6 +352,14 @@ enum FileOrLink {
Link(CString),
}

fn sanitize_name_at(inode: Inode, name: &CStr) -> &CStr {
if inode == fuse::ROOT_ID && name == c".." {
c"."
} else {
name
}
}

impl PassthroughFs {
pub fn new(cfg: Config) -> io::Result<PassthroughFs> {
let fd = if let Some(fd) = cfg.proc_sfd_rawfd {
Expand Down Expand Up @@ -491,6 +499,7 @@ impl PassthroughFs {
}

fn do_lookup(&self, parent: Inode, name: &CStr) -> io::Result<Entry> {
let name = sanitize_name_at(parent, name);
let p = self
.inodes
.read()
Expand Down Expand Up @@ -761,6 +770,8 @@ impl PassthroughFs {
}

fn do_unlink(&self, parent: Inode, name: &CStr, flags: libc::c_int) -> io::Result<()> {
let name = sanitize_name_at(parent, name);

let data = self
.inodes
.read()
Expand Down Expand Up @@ -1003,6 +1014,7 @@ impl FileSystem for PassthroughFs {
umask: u32,
extensions: Extensions,
) -> io::Result<Entry> {
let name = sanitize_name_at(parent, name);
if extensions.secctx.is_some() {
unimplemented!("SECURITY_CTX is not supported and should not be used by the guest");
}
Expand All @@ -1026,6 +1038,7 @@ impl FileSystem for PassthroughFs {
}

fn rmdir(&self, _ctx: Context, parent: Inode, name: &CStr) -> io::Result<()> {
let name = sanitize_name_at(parent, name);
self.do_unlink(parent, name, libc::AT_REMOVEDIR)
}

Expand Down Expand Up @@ -1106,6 +1119,7 @@ impl FileSystem for PassthroughFs {
umask: u32,
extensions: Extensions,
) -> io::Result<(Entry, Option<Handle>, OpenOptions)> {
let name = sanitize_name_at(parent, name);
if extensions.secctx.is_some() {
unimplemented!("SECURITY_CTX is not supported and should not be used by the guest");
}
Expand Down Expand Up @@ -1396,6 +1410,9 @@ impl FileSystem for PassthroughFs {
newname: &CStr,
flags: u32,
) -> io::Result<()> {
let oldname = sanitize_name_at(olddir, oldname);
let newname = sanitize_name_at(newdir, newname);

let old_inode = self
.inodes
.read()
Expand Down Expand Up @@ -1441,6 +1458,7 @@ impl FileSystem for PassthroughFs {
umask: u32,
extensions: Extensions,
) -> io::Result<Entry> {
let name = sanitize_name_at(parent, name);
if extensions.secctx.is_some() {
unimplemented!("SECURITY_CTX is not supported and should not be used by the guest");
}
Expand Down Expand Up @@ -1478,6 +1496,8 @@ impl FileSystem for PassthroughFs {
newparent: Inode,
newname: &CStr,
) -> io::Result<Entry> {
let newname = sanitize_name_at(newparent, newname);

let data = self
.inodes
.read()
Expand Down Expand Up @@ -1521,6 +1541,8 @@ impl FileSystem for PassthroughFs {
name: &CStr,
extensions: Extensions,
) -> io::Result<Entry> {
let name = sanitize_name_at(parent, name);

// Set security context on symlink.
if extensions.secctx.is_some() {
unimplemented!("SECURITY_CTX is not supported and should not be used by the guest");
Expand Down Expand Up @@ -1704,6 +1726,7 @@ impl FileSystem for PassthroughFs {
value: &[u8],
flags: u32,
) -> io::Result<()> {
let name = sanitize_name_at(inode, name);
if !self.cfg.xattr {
return Err(io::Error::from_raw_os_error(libc::ENOSYS));
}
Expand Down Expand Up @@ -1752,6 +1775,7 @@ impl FileSystem for PassthroughFs {
name: &CStr,
size: u32,
) -> io::Result<GetxattrReply> {
let name = sanitize_name_at(inode, name);
if !self.cfg.xattr {
return Err(io::Error::from_raw_os_error(libc::ENOSYS));
}
Expand Down Expand Up @@ -1844,6 +1868,7 @@ impl FileSystem for PassthroughFs {
}

fn removexattr(&self, _ctx: Context, inode: Inode, name: &CStr) -> io::Result<()> {
let name = sanitize_name_at(inode, name);
if !self.cfg.xattr {
return Err(io::Error::from_raw_os_error(libc::ENOSYS));
}
Expand Down
2 changes: 2 additions & 0 deletions src/devices/src/virtio/fs/mod.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -61,6 +61,8 @@ pub enum FsError {
/// A C string parameter is invalid.
InvalidCString(FromBytesWithNulError),
InvalidCString2(FromVecWithNulError),
/// Given string is not a valid filename
InvalidFilename,
/// The `len` field of the header is too small.
InvalidHeaderLength,
/// The `size` field of the `SetxattrIn` message does not match the length
Expand Down
32 changes: 21 additions & 11 deletions src/devices/src/virtio/fs/server.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -192,7 +192,7 @@ impl<F: FileSystem + Sync> Server<F> {

r.read_exact(&mut buf).map_err(Error::DecodeMessage)?;

let name = bytes_to_cstr(buf.as_ref())?;
let name = filename_from_bytes(buf.as_ref())?;

match self
.fs
Expand Down Expand Up @@ -310,9 +310,11 @@ impl<F: FileSystem + Sync> Server<F> {

match self.fs.symlink(
Context::from(in_header),
// Target of the symlink can be a path - it can contain '/'
bytes_to_cstr(linkname)?,
in_header.nodeid.into(),
bytes_to_cstr(name)?,
// The symlink cannot contain '/'
filename_from_bytes(name)?,
extensions,
) {
Ok(entry) => {
Expand Down Expand Up @@ -346,7 +348,7 @@ impl<F: FileSystem + Sync> Server<F> {
match self.fs.mknod(
Context::from(in_header),
in_header.nodeid.into(),
bytes_to_cstr(name)?,
filename_from_bytes(name)?,
mode,
rdev,
umask,
Expand Down Expand Up @@ -381,7 +383,7 @@ impl<F: FileSystem + Sync> Server<F> {
match self.fs.mkdir(
Context::from(in_header),
in_header.nodeid.into(),
bytes_to_cstr(name)?,
filename_from_bytes(name)?,
mode,
umask,
extensions,
Expand All @@ -406,7 +408,7 @@ impl<F: FileSystem + Sync> Server<F> {
match self.fs.unlink(
Context::from(in_header),
in_header.nodeid.into(),
bytes_to_cstr(&name)?,
filename_from_bytes(&name)?,
) {
Ok(()) => reply_ok(None::<u8>, None, in_header.unique, w),
Err(e) => reply_error(e, in_header.unique, w),
Expand All @@ -424,7 +426,7 @@ impl<F: FileSystem + Sync> Server<F> {
match self.fs.rmdir(
Context::from(in_header),
in_header.nodeid.into(),
bytes_to_cstr(&name)?,
filename_from_bytes(&name)?,
) {
Ok(()) => reply_ok(None::<u8>, None, in_header.unique, w),
Err(e) => reply_error(e, in_header.unique, w),
Expand Down Expand Up @@ -460,9 +462,9 @@ impl<F: FileSystem + Sync> Server<F> {
match self.fs.rename(
Context::from(in_header),
in_header.nodeid.into(),
bytes_to_cstr(oldname)?,
filename_from_bytes(oldname)?,
newdir.into(),
bytes_to_cstr(newname)?,
filename_from_bytes(newname)?,
flags,
) {
Ok(()) => reply_ok(None::<u8>, None, in_header.unique, w),
Expand Down Expand Up @@ -500,7 +502,7 @@ impl<F: FileSystem + Sync> Server<F> {
Context::from(in_header),
oldnodeid.into(),
in_header.nodeid.into(),
bytes_to_cstr(&name)?,
filename_from_bytes(&name)?,
) {
Ok(entry) => {
let out = EntryOut::from(entry);
Expand Down Expand Up @@ -755,7 +757,7 @@ impl<F: FileSystem + Sync> Server<F> {
match self.fs.getxattr(
Context::from(in_header),
in_header.nodeid.into(),
bytes_to_cstr(&name)?,
filename_from_bytes(&name)?,
size,
) {
Ok(GetxattrReply::Value(val)) => reply_ok(None::<u8>, Some(&val), in_header.unique, w),
Expand Down Expand Up @@ -1115,7 +1117,7 @@ impl<F: FileSystem + Sync> Server<F> {
match self.fs.create(
Context::from(in_header),
in_header.nodeid.into(),
bytes_to_cstr(name)?,
filename_from_bytes(name)?,
mode,
flags,
umask,
Expand Down Expand Up @@ -1475,6 +1477,14 @@ fn bytes_to_cstr(buf: &[u8]) -> Result<&CStr> {
CStr::from_bytes_with_nul(buf).map_err(Error::InvalidCString)
}

fn filename_from_bytes(buf: &[u8]) -> Result<&CStr> {
let cstr = bytes_to_cstr(buf)?;
if cstr.to_bytes().contains(&b'/') {
return Err(Error::InvalidFilename);
}
Ok(cstr)
}

fn add_dirent(
cursor: &mut Writer,
max: u32,
Expand Down
Loading