      1
      2
      3
      4
      5
      6
      7
      8
      9
     10
     11
     12
     13
     14
     15
     16
     17
     18
     19
     20
     21
     22
     23
     24
     25
     26
     27
     28
     29
     30
     31
     32
     33
     34
     35
     36
     37
     38
     39
     40
     41
     42
     43
     44
     45
     46
     47
     48
     49
     50
     51
     52
     53
     54
     55
     56
     57
     58
     59
     60
     61
     62
     63
     64
     65
     66
     67
     68
     69
     70
     71
     72
     73
     74
     75
     76
     77
     78
     79
     80
     81
     82
     83
     84
     85
     86
     87
     88
     89
     90
     91
     92
     93
     94
     95
     96
     97
     98
     99
    100
    101
    102
    103
    104
    105
    106
    107
    108
    109
    110
    111
    112
    113
    114
    115
    116
    117
    118
    119
    120
    121
    122
    123
    124
    125
    126
    127
    128
    129
    130
    131
    132
    133
    134
    135
    136
    137
    138
    139
    140
    141
    142
    143
    144
    145
    146
    147
    148
    149
    150
    151
    152
    153
    154
    155
    156
    157
    158
    159
    160
    161
    162
    163
    164
    165
    166
    167
    168
    169
    170
    171
    172
    173
    174
    175
    176
    177
    178
    179
    180
    181
    182
    183
    184
    185
    186
    187
    188
    189
    190
    191
    192
    193
    194
    195
    196
    197
    198
    199
    200
    201
    202
    203
    204
    205
    206
    207
    208
    209
    210
    211
    212
    213
    214
    215
    216
    217
    218
    219
    220
    221
    222
    223
    224
    225
    226
    227
    228
    229
    230
    231
    232
    233
    234
    235
    236
    237
    238
    239
    240
    241
    242
    243
    244
    245
    246
    247
    248
    249
    250
    251
    252
    253
    254
    255
    256
    257
    258
    259
    260
    261
    262
    263
    264
    265
    266
    267
    268
    269
    270
    271
    272
    273
    274
    275
    276
    277
    278
    279
    280
    281
    282
    283
    284
    285
    286
    287
    288
    289
    290
    291
    292
    293
    294
    295
    296
    297
    298
    299
    300
    301
    302
    303
    304
    305

    // Copyright 2015-2016 Brian Smith.
    //
    // Permission to use, copy, modify, and/or distribute this software for any
    // purpose with or without fee is hereby granted, provided that the above
    // copyright notice and this permission notice appear in all copies.
    //
    // THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
    // WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
    // MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
    // SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    // WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
    // OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
    // CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

    //! Cryptographic pseudo-random number generation.
    //!
    //! An application should create a single `SystemRandom` and then use it for
    //! all randomness generation. Functions that generate random bytes should take
    //! a `&SecureRandom` parameter instead of instantiating their own. Besides
    //! being more efficient, this also helps document where non-deterministic
    //! (random) outputs occur. Taking a reference to a `SecureRandom` also helps
    //! with testing techniques like fuzzing, where it is useful to use a
    //! (non-secure) deterministic implementation of `SecureRandom` so that results
    //! can be replayed. Following this pattern also may help with sandboxing
    //! (seccomp filters on Linux in particular). See `SystemRandom`'s
    //! documentation for more details.

    use error;

    /// A secure random number generator.
    pub trait SecureRandom {
        /// Fills `dest` with random bytes.
        fn fill(&self, dest: &mut [u8]) -> Result<(), error::Unspecified>;
    }

    /// A secure random number generator where the random values come directly
    /// from the operating system.
    ///
    /// A single `SystemRandom` may be shared across multiple threads safely.
    ///
    /// `new()` is guaranteed to always succeed and to have low latency; it won't
    /// try to open or read from a file or do similar things. The first call to
    /// `fill()` may block a substantial amount of time since any and all
    /// initialization is deferred to it. Therefore, it may be a good idea to call
    /// `fill()` once at a non-latency-sensitive time to minimize latency for
    /// future calls.
    ///
    /// On Linux, `fill()` will use the [`getrandom`] syscall. If the kernel is too
    /// old to support `getrandom` then by default `fill()` falls back to reading
    /// from `/dev/urandom`. This decision is made the first time `fill`
    /// *succeeds*. The fallback to `/dev/urandom` can be disabled by disabling the
    /// `dev_urandom_fallback` default feature; this should be done whenever the
    /// target system is known to support `getrandom`. Library crates should avoid
    /// explicitly enabling the `dev_urandom_fallback` feature.
    ///
    /// On macOS and iOS, `fill()` is implemented using `SecRandomCopyBytes`.
    ///
    /// On Redox, `fill()` is implemented by reading from `rand:`.
    ///
    /// On Windows, `fill` is implemented using the platform's API for secure
    /// random number generation.
    ///
    /// Otherwise, `fill()` is implemented by reading from `/dev/urandom`. (This is
    /// something that should be improved for any platform that adds something
    /// better.)
    ///
    /// When `/dev/urandom` is used, a file handle for `/dev/urandom` won't be
    /// opened until `fill` is called. In particular, `SystemRandom::new()` will
    /// not open `/dev/urandom` or do other potentially-high-latency things. The
    /// file handle will never be closed, until the operating system closes it at
    /// process shutdown. All instance of `SystemRandom` will share a single file
    /// handle.
    ///
    /// On Linux, to properly implement seccomp filtering when the
    /// `dev_urandom_fallback` default feature is disabled, allow `getrandom`
    /// through. When the fallback is enabled, allow file opening, `getrandom`,
    /// and `read` up until the first call to `fill()` succeeds. After that, allow
    /// `getrandom` and `read`.
    ///
    /// [`getrandom`]: http://man7.org/linux/man-pages/man2/getrandom.2.html
    pub struct SystemRandom;

    impl SystemRandom {
        /// Constructs a new `SystemRandom`.
        #[inline(always)]
        pub fn new() -> SystemRandom { SystemRandom }
    }

    impl SecureRandom for SystemRandom {
        #[inline(always)]
        fn fill(&self, dest: &mut [u8]) -> Result<(), error::Unspecified> {
            fill_impl(dest)
        }
    }

    #[cfg(not(any(target_os = "linux",
                  target_os = "macos",
                  target_os = "ios",
                  windows)))]
    use self::urandom::fill as fill_impl;

    #[cfg(any(all(target_os = "linux", not(feature = "dev_urandom_fallback")),
              windows))]
    use self::sysrand::fill as fill_impl;

    #[cfg(all(target_os = "linux", feature = "dev_urandom_fallback"))]
    use self::sysrand_or_urandom::fill as fill_impl;

    #[cfg(any(target_os = "macos", target_os = "ios"))]
    use self::darwin::fill as fill_impl;

    #[cfg(target_os = "linux")]
    mod sysrand_chunk {
        use {c, error};
        use libc;

        extern {
            static GFp_SYS_GETRANDOM: c::long;
        }

        #[inline]
        pub fn chunk(dest: &mut [u8]) -> Result<usize, error::Unspecified> {
            let chunk_len: c::size_t = dest.len();
            let flags: c::uint = 0;
            let r = unsafe {
                libc::syscall(GFp_SYS_GETRANDOM, dest.as_mut_ptr(), chunk_len, flags)
            };
            if r < 0 {
                if unsafe { *libc::__errno_location() } == libc::EINTR {
                    // If an interrupt occurs while getrandom() is blocking to wait
                    // for the entropy pool, then EINTR is returned. Returning 0
                    // will cause the caller to try again.
                    return Ok(0);
                }
                return Err(error::Unspecified);
            }
            Ok(r as usize)
        }
    }

    #[cfg(windows)]
    mod sysrand_chunk {
        use core;
        use {c, error};

        #[link(name = "Advapi32")]
        extern "system" {
            #[link_name = "SystemFunction036"]
            fn RtlGenRandom(random_buffer: *mut u8,
                            random_buffer_length: c::win32::ULONG)
                            -> c::win32::BOOLEAN;
        }

        #[inline]
        pub fn chunk(dest: &mut [u8]) -> Result<usize, error::Unspecified> {
            assert!(core::mem::size_of::<usize>() >=
                        core::mem::size_of::<c::win32::ULONG>());
            let max_chunk_len = c::win32::ULONG::from(0u32).wrapping_sub(1) as usize;
            assert_eq!(max_chunk_len, 0xffff_ffff);
            let len = core::cmp::min(dest.len(), max_chunk_len);

            if unsafe { RtlGenRandom(dest.as_mut_ptr(), len as c::win32::ULONG) }
                    == 0 {
                return Err(error::Unspecified);
            }

            Ok(len)
        }
    }

    #[cfg(any(target_os = "linux", windows))]
    mod sysrand {
        use error;
        use super::sysrand_chunk::chunk;

        pub fn fill(dest: &mut [u8]) -> Result<(), error::Unspecified> {
            let mut read_len = 0;
            while read_len < dest.len() {
                let chunk_len = chunk(&mut dest[read_len..])?;
                read_len += chunk_len;
            }
            Ok(())
        }
    }

    // Keep the `cfg` conditions in sync with the conditions in lib.rs.
    #[cfg(all(any(target_os = "redox", unix),
              not(any(target_os = "macos", target_os = "ios")),
              not(all(target_os = "linux",
                      not(feature = "dev_urandom_fallback")))))]
    mod urandom {
        use std;
        use error;

        pub fn fill(dest: &mut [u8]) -> Result<(), error::Unspecified> {
            #[cfg(target_os = "redox")]
            static RANDOM_PATH: &'static str = "rand:";
            #[cfg(unix)]
            static RANDOM_PATH: &'static str = "/dev/urandom";

            lazy_static! {
                static ref FILE: Result<std::fs::File, std::io::Error> =
                    std::fs::File::open(RANDOM_PATH);
            }

            match *FILE {
                Ok(ref file) => {
                    use std::io::Read;
                    (&*file).read_exact(dest).map_err(|_| error::Unspecified)
                },
                Err(_) => Err(error::Unspecified),
            }
        }
    }

    // Keep the `cfg` conditions in sync with the conditions in lib.rs.
    #[cfg(all(target_os = "linux", feature = "dev_urandom_fallback"))]
    mod sysrand_or_urandom {
        use error;

        enum Mechanism {
            Sysrand,
            DevURandom,
        }

        pub fn fill(dest: &mut [u8]) -> Result<(), error::Unspecified> {
            lazy_static! {
                static ref MECHANISM: Mechanism = {
                    let mut dummy = [0u8; 1];
                    if super::sysrand_chunk::chunk(&mut dummy[..]).is_err() {
                        Mechanism::DevURandom
                    } else {
                        Mechanism::Sysrand
                    }
                };
            }

            match *MECHANISM {
                Mechanism::Sysrand => super::sysrand::fill(dest),
                Mechanism::DevURandom => super::urandom::fill(dest),
            }
        }
    }

    #[cfg(any(target_os = "macos", target_os = "ios"))]
    mod darwin {
        use c;
        use error;

        pub fn fill(dest: &mut [u8]) -> Result<(), error::Unspecified> {
            let r = unsafe {
                SecRandomCopyBytes(kSecRandomDefault, dest.len(),
                                   dest.as_mut_ptr())
            };
            match r {
                0 => Ok(()),
                _ => Err(error::Unspecified),
            }
        }

        // XXX: This is emulating an opaque type with a non-opaque type. TODO: Fix
        // this when
        // https://github.com/rust-lang/rfcs/pull/1861#issuecomment-274613536 is
        // resolved.
        #[repr(C)]
        struct SecRandomRef([u8; 0]);

        #[link(name = "Security", kind = "framework")]
        extern {
            static kSecRandomDefault: &'static SecRandomRef;

            // For now `rnd` must be `kSecRandomDefault`.
            fn SecRandomCopyBytes(rnd: &'static SecRandomRef, count: c::size_t,
                                  bytes: *mut u8) -> c::int;
        }
    }

    #[cfg(test)]
    mod tests {
        use rand;
        use rand::SecureRandom;

        #[test]
        fn test_system_random_lengths() {
            // Test that `fill` succeeds for various interesting lengths. `256` and
            // multiples thereof are interesting because that's an edge case for
            // `getrandom` on Linux.
            let lengths = [0, 1, 2, 3, 96, 255, 256, 257, 511, 512, 513, 4096];

            for len in lengths.iter() {
                let mut buf = vec![0; *len];

                let rng = rand::SystemRandom::new();
                assert!(rng.fill(&mut buf).is_ok());

                // If `len` < 96 then there's a big chance of false positives, but
                // otherwise the likelihood of a false positive is so too low to
                // worry about.
                if *len >= 96 {
                    assert!(buf.iter().any(|x| *x != 0));
                }
            }
        }
    }

# Help

## Keyboard Shortcuts

?
  Show this help dialog
S
  Focus the search field
⇤
  Move up in search results
⇥
  Move down in search results
⏎
  Go to active search result
+
  Collapse/expand all sections

## Search Tricks

Prefix searches with a type followed by a colon (e.g. `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g. `vec -> usize` or `* -> vec`)