Auto merge of #44220 - kennytm:fix-44216-instance-plus-max-duration-should-panic, r=alexcrichton

Properly detect overflow in Instance ± Duration.

Fix #44216.
Fix #42622

The computation `Instant::now() + Duration::from_secs(u64::max_value())` now panics. The call `receiver.recv_timeout(Duration::from_secs(u64::max_value()))`, which involves such time addition, will also panic.

The reason #44216 arises is because of an unchecked cast from `u64` to `i64`, making the duration equivalent to -1 second.

Note that the current implementation is over-conservative, since e.g. (-2⁶²) + (2⁶³) is perfectly fine for an `i64`, yet this is rejected because (2⁶³) overflows the `i64`.

1 files changed, 15 insertions, 7 deletions

diff --git a/src/libstd/sys/unix/time.rs b/src/libstd/sys/unix/time.rs
index a1ad94872de..c1bea95ce91 100644
--- a/src/libstd/sys/unix/time.rs
+++ b/src/libstd/sys/unix/time.rs
@@ -13,6 +13,7 @@ use libc;
 use time::Duration;
 
 pub use self::inner::{Instant, SystemTime, UNIX_EPOCH};
+use convert::TryInto;
 
 const NSEC_PER_SEC: u64 = 1_000_000_000;
 
@@ -41,8 +42,12 @@ impl Timespec {
     }
 
     fn add_duration(&self, other: &Duration) -> Timespec {
-        let secs = (self.t.tv_sec as i64).checked_add(other.as_secs() as i64);
-        let mut secs = secs.expect("overflow when adding duration to time");
+        let mut secs = other
+            .as_secs()
+            .try_into() // <- target type would be `libc::time_t`
+            .ok()
+            .and_then(|secs| self.t.tv_sec.checked_add(secs))
+            .expect("overflow when adding duration to time");
 
         // Nano calculations can't overflow because nanos are <1B which fit
         // in a u32.
@@ -54,16 +59,19 @@ impl Timespec {
         }
         Timespec {
             t: libc::timespec {
-                tv_sec: secs as libc::time_t,
+                tv_sec: secs,
                 tv_nsec: nsec as libc::c_long,
             },
         }
     }
 
     fn sub_duration(&self, other: &Duration) -> Timespec {
-        let secs = (self.t.tv_sec as i64).checked_sub(other.as_secs() as i64);
-        let mut secs = secs.expect("overflow when subtracting duration \
-                                    from time");
+        let mut secs = other
+            .as_secs()
+            .try_into() // <- target type would be `libc::time_t`
+            .ok()
+            .and_then(|secs| self.t.tv_sec.checked_sub(secs))
+            .expect("overflow when subtracting duration from time");
 
         // Similar to above, nanos can't overflow.
         let mut nsec = self.t.tv_nsec as i32 - other.subsec_nanos() as i32;
@@ -74,7 +82,7 @@ impl Timespec {
         }
         Timespec {
             t: libc::timespec {
-                tv_sec: secs as libc::time_t,
+                tv_sec: secs,
                 tv_nsec: nsec as libc::c_long,
             },
         }