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vhost_user_fs: Allow callers to provide a fd for /proc/self/fd

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Allow callers to provide a file descriptor for /proc/self/fd. This is
useful for sandboxing, as we may be running in a namespace that
doesn't have access to /proc.

Signed-off-by: Sergio Lopez <slp@redhat.com>
This commit is contained in:
Sergio Lopez 2020-04-24 12:49:25 +02:00 committed by Sebastien Boeuf
parent 831cff3fee
commit fa844865a5
1 changed files with 27 additions and 13 deletions
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40
vhost_user_fs/src/passthrough.rs
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@ -238,6 +238,13 @@ pub struct Config {
///
/// The default value for this options is `false`.
pub xattr: bool,
/// Optional file descriptor for /proc/self/fd. Callers can obtain a file descriptor and pass it
/// here, so there's no need to open it in PassthroughFs::new(). This is specially useful for
/// sandboxing.
///
/// The default is `None`.
pub proc_sfd_rawfd: Option<RawFd>,
}
impl Default for Config {
@ -249,6 +256,7 @@ impl Default for Config {
writeback: false,
root_dir: String::from("/"),
xattr: false,
proc_sfd_rawfd: None,
}
}
}
@ -286,22 +294,28 @@ pub struct PassthroughFs {
impl PassthroughFs {
pub fn new(cfg: Config) -> io::Result<PassthroughFs> {
// Safe because this is a constant value and a valid C string.
let proc_cstr = unsafe { CStr::from_bytes_with_nul_unchecked(PROC_CSTR) };
let fd = if let Some(fd) = cfg.proc_sfd_rawfd {
fd
} else {
// Safe because this is a constant value and a valid C string.
let proc_cstr = unsafe { CStr::from_bytes_with_nul_unchecked(PROC_CSTR) };
// Safe because this doesn't modify any memory and we check the return value.
let fd = unsafe {
libc::openat(
libc::AT_FDCWD,
proc_cstr.as_ptr(),
libc::O_PATH | libc::O_NOFOLLOW | libc::O_CLOEXEC,
)
// Safe because this doesn't modify any memory and we check the return value.
let fd = unsafe {
libc::openat(
libc::AT_FDCWD,
proc_cstr.as_ptr(),
libc::O_PATH | libc::O_NOFOLLOW | libc::O_CLOEXEC,
)
};
if fd < 0 {
return Err(io::Error::last_os_error());
}
fd
};
if fd < 0 {
return Err(io::Error::last_os_error());
}
// Safe because we just opened this fd.
// Safe because we just opened this fd or it was provided by our caller.
let proc_self_fd = unsafe { File::from_raw_fd(fd) };
Ok(PassthroughFs {