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Reference outlives the value it points to (segfault) #37418

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benschulz opened this issue Oct 26, 2016 · 4 comments
Closed

Reference outlives the value it points to (segfault) #37418

benschulz opened this issue Oct 26, 2016 · 4 comments

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@benschulz
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A is value referenced both outside as well as inside a closure and the closure is boxed and (indirectly) returned. A segfault is raised when the closure is eventually invoked and the reference dereferenced.

I tried this code:

I failed to create an SSCEE for the bug, however, I originally stumbled over the behaviour here. Semantically the code contains the same error as the following code.

fn foo() -> Box<Fn() -> usize> {
    let x = 0;
    Box::new(|| x)
}

fn main() {
    foo()();
}

I expected to see this happen: The compiler should force me to mark the closure as move and resolve the resulting errors as it does with the small example given above.

Instead, this happened: The code compiles as is and segfaults when the test is run (simply via cargo testing the repo). The segfault happens when dereferencing expected_key2 inside the closure. It does not occur when marking the closure as move and passing &*expected_key instead of &*expected_key2 to store.write_blob.

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rustc --version --verbose:
rustc 1.12.1 (d4f3940 2016-10-19)
binary: rustc
commit-hash: d4f3940
commit-date: 2016-10-19
host: x86_64-unknown-linux-gnu
release: 1.12.1

Backtrace (from gdb):

#0  0x000055555558cbd9 in object_store::ops::write_blob::WriteBlob::new::_$u7b$$u7b$closure$u7d$$u7d$::_$u7b$$u7b$closure$u7d$$u7d$::h729166bb3b5a29fc ()
#1  0x000055555558d773 in _$LT$futures..then..Then$LT$A$C$$u20$B$C$$u20$F$GT$$u20$as$u20$futures..Future$GT$::poll::_$u7b$$u7b$closure$u7d$$u7d$::h3985deb15ce38518 ()
#2  0x0000555555580a22 in {{inlined-root}}::poll<object_store::hash::verify::Verify<std::io::cursor::Cursor<collections::string::String>, std::fs::File, object_store::hash::Sha256Hasher, object_store::hash::Sha256Hash>,futures::done::Done<(), std::io::error::Error>,closure,closure> (self=0x7ffff5e5b068, f=...)
    at /home/benshu/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.2/src/chain.rs:38
#3  0x0000555555588afc in {{inlined-root}}::poll<object_store::hash::verify::Verify<std::io::cursor::Cursor<collections::string::String>, std::fs::File, object_store::hash::Sha256Hasher, object_store::hash::Sha256Hash>,futures::done::Done<(), std::io::error::Error>,closure> (self=0x7ffff5e5b068)
    at /home/benshu/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.2/src/then.rs:31
#4  0x00005555555673b0 in {{inlined-root}}::poll<closure,futures::then::Then<object_store::hash::verify::Verify<std::io::cursor::Cursor<collections::string::String>, std::fs::File, object_store::hash::Sha256Hasher, object_store::hash::Sha256Hash>, futures::done::Done<(), std::io::error::Error>, closure>,(),std::io::error::Error> (self=0x7ffff5e5b000)
    at /home/benshu/git-repos/object-store-rs/src/intermediate_path.rs:52
#5  0x00005555555867c0 in {{inlined-root}}::poll<object_store::blob::Blob,object_store::intermediate_path::IntermediatePath<closure, futures::then::Then<object_store::hash::verify::Verify<std::io::cursor::Cursor<collections::string::String>, std::fs::File, object_store::hash::Sha256Hasher, object_store::hash::Sha256Hash>, futures::done::Done<(), std::io::error::Error>, closure>>,closure> (self=0x7ffff5e5b000) at /home/benshu/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.2/src/map.rs:29
#6  0x0000555555587279 in {{inlined-root}}::poll<std::io::error::Error,futures::map::Map<object_store::intermediate_path::IntermediatePath<closure, futures::then::Then<object_store::hash::verify::Verify<std::io::cursor::Cursor<collections::string::String>, std::fs::File, object_store::hash::Sha256Hasher, object_store::hash::Sha256Hash>, futures::done::Done<(), std::io::error::Error>, closure>>, closure>,closure> (self=0x7ffff5e5b000) at /home/benshu/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.2/src/map_err.rs:29
#7  0x0000555555576e61 in {{inlined-root}}::poll<Future> (self=0x7ffff5e3f030) at /home/benshu/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.2/src/lib.rs:231
#8  0x00005555555be8a1 in {{inlined-root}}::poll<Future> (self=0x7ffff63fe830) at /home/benshu/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.2/src/lib.rs:231
#9  0x00005555555cad9c in object_store::ops::write_blob::{{impl}}::poll (self=0x7ffff63fe830) at /home/benshu/git-repos/object-store-rs/src/ops/write_blob.rs:53
#10 0x00005555555811f8 in {{inlined-root}}::poll<object_store::ops::write_blob::WriteBlob,object_store::ops::write_tree::WriteTree,closure,closure> (self=0x7ffff63fe828, f=...)
    at /home/benshu/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.2/src/chain.rs:25
#11 0x0000555555589efc in {{inlined-root}}::poll<object_store::ops::write_blob::WriteBlob,object_store::ops::write_tree::WriteTree,closure> (self=0x7ffff63fe828)
    at /home/benshu/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.2/src/and_then.rs:31
#12 0x0000555555586b00 in {{inlined-root}}::poll<(),futures::and_then::AndThen<object_store::ops::write_blob::WriteBlob, object_store::ops::write_tree::WriteTree, closure>,closure> (
    self=0x7ffff63fe828) at /home/benshu/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.2/src/map.rs:29
#13 0x00005555555874b8 in {{inlined-root}}::poll<(),futures::map::Map<futures::and_then::AndThen<object_store::ops::write_blob::WriteBlob, object_store::ops::write_tree::WriteTree, closure>, closure>,closure> (self=0x7ffff63fe828) at /home/benshu/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.2/src/map_err.rs:29
#14 0x000055555558d145 in _$LT$futures..task..Spawn$LT$F$GT$$GT$::poll_future::_$u7b$$u7b$closure$u7d$$u7d$::h3e038fa9311180df ()
    at /buildslave/rust-buildbot/slave/stable-dist-rustc-linux/build/obj/../src/libstd/collections/hash/table.rs:1040
#15 0x000055555558d187 in _$LT$futures..task..Spawn$LT$T$GT$$GT$::enter::_$u7b$$u7b$closure$u7d$$u7d$::hb84cd279a381c4af ()
    at /buildslave/rust-buildbot/slave/stable-dist-rustc-linux/build/obj/../src/libstd/collections/hash/table.rs:1040
#16 0x000055555558d2a1 in futures::task::set::_$u7b$$u7b$closure$u7d$$u7d$::h9de1fc90a64552d1 ()
    at /buildslave/rust-buildbot/slave/stable-dist-rustc-linux/build/obj/../src/libstd/collections/hash/table.rs:1040
#17 0x0000555555574071 in {{inlined-root}}::with<core::cell::Cell<(*const futures::task::Task, *const core::cell::RefCell<std::collections::hash::map::HashMap<core::any::TypeId, Box<Opaque>, core::hash::BuildHasherDefault<futures::task::data::IdHasher>>>)>,closure,core::result::Result<futures::poll::Async<()>, ()>> (
    self=0x5555558dbb50 <futures::task::CURRENT_TASK::h4df43acd7ab31fdb>, f=...) at /buildslave/rust-buildbot/slave/stable-dist-rustc-linux/build/obj/../src/libstd/thread/local.rs:245
#18 0x0000555555587f9b in {{inlined-root}}::set<closure,core::result::Result<futures::poll::Async<()>, ()>> (task=0x7ffff63fdd08, data=0x7ffff63fe860, f=...)
    at /home/benshu/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.2/src/task/mod.rs:72
#19 0x0000555555571bab in {{inlined-root}}::enter<futures::map_err::MapErr<futures::map::Map<futures::and_then::AndThen<object_store::ops::write_blob::WriteBlob, object_store::ops::write_tree::WriteTree, closure>, closure>, closure>,closure,core::result::Result<futures::poll::Async<()>, ()>> (self=0x7ffff63fe828, unpark=..., f=...)
    at /home/benshu/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.2/src/task/mod.rs:304
#20 0x0000555555571a1b in {{inlined-root}}::poll_future<futures::map_err::MapErr<futures::map::Map<futures::and_then::AndThen<object_store::ops::write_blob::WriteBlob, object_store::ops::write_tree::WriteTree, closure>, closure>, closure>> (self=0x7ffff63fe828, unpark=...) at /home/benshu/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-0.1.2/src/task/mod.rs:217
---Type <return> to continue, or q <return> to quit---
#21 0x000055555558c688 in tokio_core::reactor::Core::run::_$u7b$$u7b$closure$u7d$$u7d$::hfb022cd8bb9d6df8 ()
    at /buildslave/rust-buildbot/slave/stable-dist-rustc-linux/build/obj/../src/libstd/collections/hash/table.rs:1040
#22 0x000055555560908a in tokio_core::reactor::{{impl}}::_run::{{closure}} () at /home/benshu/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-core-0.1.0/src/reactor/mod.rs:232
#23 0x00005555555efb3f in {{inlined-root}}::set<tokio_core::reactor::Core,closure,bool> (self=0x5555558db7f0 <tokio_core::reactor::CURRENT_LOOP::hb69805ae44045245>, t=0x7ffff63feb50, f=...)
    at /home/benshu/.cargo/registry/src/github.com-1ecc6299db9ec823/scoped-tls-0.1.0/src/lib.rs:135
#24 0x00005555556040a1 in tokio_core::reactor::Core::_run (self=0x7ffff63feb50, done=...)
    at /home/benshu/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-core-0.1.0/src/reactor/mod.rs:232
#25 0x0000555555568e64 in {{inlined-root}}::run<futures::map_err::MapErr<futures::map::Map<futures::and_then::AndThen<object_store::ops::write_blob::WriteBlob, object_store::ops::write_tree::WriteTree, closure>, closure>, closure>> (self=0x7ffff63feb50, f=...) at /home/benshu/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-core-0.1.0/src/reactor/mod.rs:217
#26 0x000055555558c25a in foo::write_object () at /home/benshu/git-repos/object-store-rs/tests/foo.rs:34
#27 0x000055555559802c in _$LT$F$u20$as$u20$alloc..boxed..FnBox$LT$A$GT$$GT$::call_box::hf1def207a373fb3f ()
#28 0x0000555555590340 in std::panicking::try::do_call::h9297bd73d4296b2b ()
#29 0x0000555555646f07 in __rust_maybe_catch_panic ()
#30 0x0000555555597a5b in _$LT$F$u20$as$u20$alloc..boxed..FnBox$LT$A$GT$$GT$::call_box::hb675dcf15ec220c3 ()
#31 0x000055555563d2e3 in std::sys::thread::Thread::new::thread_start::h57f688c224d4fa4d ()
#32 0x00007ffff79c0454 in start_thread () from /usr/lib/libpthread.so.0
#33 0x00007ffff74ec7df in clone () from /usr/lib/libc.so.6
@Stebalien
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This looks like #18937

Trait definition: https://github.com/benschulz/object-store-rs/blob/7d6ecea8a1700de2c9dfe8ebb148e58c7265cac7/src/store.rs#L153

Function with more restrictive lifetimes: https://github.com/benschulz/object-store-rs/blob/7d6ecea8a1700de2c9dfe8ebb148e58c7265cac7/src/store.rs#L167

FYI, while looking through your code, I noticed https://github.com/benschulz/orc/blob/320651873e964eefd79d360adf7f3b4bba7dfb7c/src/lib.rs#L150. Transmuting an immutable reference into a mutable reference is never considered safe.

@benschulz
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Ah, this does look like an instance of the issue described in #18937. Closing this issue.

(Also thanks for the audit. That's actually dead code.)

@KalitaAlexey
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Is there any way to mark this issue linked with #18937 to check this after #18937 is fixed?

@benschulz
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I subscribed to #18937 and will check once its resolved.

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@Stebalien @benschulz @KalitaAlexey