uninitialized value in nightly build with memory sanitizer

[Byter09]

I'm currently fuzzing https://github.com/jyn514/rcc and noticed some totally unrelated crashes (they're stack overflows).

In the process however I wanted to change my script that runs the latest crash files to use a nightly and sanitized version of rcc. When using -Zsanitizer=memory compilation failed. At first it showed backtrace-sys with the warning use-of-uninitialized-value, however when testing that locally again, it showed log instead.

So I went ahead, downloaded log and ran:
RUSTFLAGS="-Awarnings -Zsanitizer=memory" cargo +nightly build.

This is the output:

   Compiling log v0.4.10 (/home/btr/Projects/clion/log)
   Compiling cfg-if v0.1.10
error: failed to run custom build command for `log v0.4.10 (/home/btr/Projects/clion/log)`

Caused by:
  process didn't exit successfully: `/home/btr/Projects/clion/log/target/debug/build/log-c3142b51c95ab84c/build-script-build` (exit code: 77)
--- stderr
==37637==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x5619ff54b846  (/home/btr/Projects/clion/log/target/debug/build/log-c3142b51c95ab84c/build-script-build+0x6b846)
    #1 0x5619ff54af6b  (/home/btr/Projects/clion/log/target/debug/build/log-c3142b51c95ab84c/build-script-build+0x6af6b)
    #2 0x5619ff54a985  (/home/btr/Projects/clion/log/target/debug/build/log-c3142b51c95ab84c/build-script-build+0x6a985)
    #3 0x5619ff555b17  (/home/btr/Projects/clion/log/target/debug/build/log-c3142b51c95ab84c/build-script-build+0x75b17)
    #4 0x5619ff54a8cb  (/home/btr/Projects/clion/log/target/debug/build/log-c3142b51c95ab84c/build-script-build+0x6a8cb)
    #5 0x5619ff54b2d1  (/home/btr/Projects/clion/log/target/debug/build/log-c3142b51c95ab84c/build-script-build+0x6b2d1)
    #6 0x7f35497e6022  (/usr/lib/libc.so.6+0x27022)
    #7 0x5619ff4eb1ed  (/home/btr/Projects/clion/log/target/debug/build/log-c3142b51c95ab84c/build-script-build+0xb1ed)

SUMMARY: MemorySanitizer: use-of-uninitialized-value (/home/btr/Projects/clion/log/target/debug/build/log-c3142b51c95ab84c/build-script-build+0x6b846) 
Exiting

This is not really my area of expertise so I hope you nice people know what to do with this.

Thanks!

[sfackler]

The build script is extremely trivial: https://github.com/rust-lang/log/blob/master/build.rs

This sounds like a false positive to me I think.

[parasyte]

I hit this as well. More info in rust-lang/rust#39610

Workaround is using -Z build-std

[jyn514]

This should be closed in favor of rust-secure-code/wg#21 IMO.

[KodrAus]

Thanks for the report @Byter09!

It looks like this is all sorted upstream so I’ll go ahead and close this one now.