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std: Synchronize access to global env during exec #55939

Merged
merged 2 commits into from
Nov 15, 2018
Merged

std: Synchronize access to global env during exec #55939

merged 2 commits into from
Nov 15, 2018

Commits on Nov 14, 2018

  1. Revert "Fixes rust-lang#46775 -- don't mutate the process's environme… 

    …nt in Command::exec"

This reverts commit 36fe3b6.
    @alexcrichton
    alexcrichton committed Nov 14, 2018
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  2. std: Synchronize access to global env during exec 

    This commit, after reverting rust-lang#55359, applies a different fix for rust-lang#46775
while also fixing rust-lang#55775. The basic idea was to go back to pre-rust-lang#55359
libstd, and then fix rust-lang#46775 in a way that doesn't expose rust-lang#55775.

The issue described in rust-lang#46775 boils down to two problems:

* First, the global environment is reset during `exec` but, but if the
  `exec` call fails then the global environment was a dangling pointer
  into free'd memory as the block of memory was deallocated when
  `Command` is dropped. This is fixed in this commit by installing a
  `Drop` stack object which ensures that the `environ` pointer is
  preserved on a failing `exec`.

* Second, the global environment was accessed in an unsynchronized
  fashion during `exec`. This was fixed by ensuring that the
  Rust-specific environment lock is acquired for these system-level
  operations.

Thanks to Alex Gaynor for pioneering the solution here!

Closes rust-lang#55775

Co-authored-by: Alex Gaynor <[email protected]>
    @alexcrichton @alex
    alexcrichton and alex committed Nov 14, 2018
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