Program unexpected panic when slice start index used

[bhao-Soo]

What version of regex are you using?

1.7.1

Describe the bug at a high level.

Program range start index out of range for slice, which causing a panic.

What are the steps to reproduce the behavior?

Using auto-generated fuzz target can reproduce the behavior. it was uploaded to the issue platform.
start_index_out_of_range.zip

Similar problems were found in the fuzzy test:

• regex/src/exec.rs:715:32
• regex/src/dfa.rs:1415:45
• regex/src/dfa.rs:1444:54
• regex/src/exec.rs:702:28
• regex/src/re_trait.rs:23:23
• regex/src/re_set.rs:448:1

What is the actual behavior?

Panic happens, the program crashes.

What is the expected behavior?

Handle start index out of range without causing a panic

[BurntSushi]

I added these debug statements to the body of your main function:

    std::dbg!(_param0);
    std::dbg!(_param1);
    std::dbg!(_param2);

And then ran your program and got:

$ cargo run crash_input
   Compiling start_index_out_of_range v0.1.0 (/home/andrew/tmp/issues/regex/i948/start_index_out_of_range)
    Finished dev [unoptimized + debuginfo] target(s) in 0.30s
     Running `target/debug/start_index_out_of_range crash_input`
data = [0, 59, 0, 0, 0, 0, 0, 0, 0, 32, 0, 0, 0, 20, 59, 58, 59, 59, 1, 27, 58, 68, 59, 74, 91, 59, 59, 59, 45, 45, 93, 47, 59, 42, 31, 93, 47, 27, 58, 59, 45, 45, 45, 27, 58, 59, 59, 59, 59, 60, 59, 59, 59, 58, 0]
data len = 55
[main.rs:88] _param0 = "\0 \0\0\0\u{14};:;;\u{1}\u{1b}:D;J[;;;--]"
[main.rs:89] _param1 = "/;*\u{1f}]/\u{1b}:;---\u{1b}:;;;;<;;;:\0"
[main.rs:90] _param2 = 16607023625928704
thread 'main' panicked at 'range start index 16607023625928704 out of range for slice of length 24', /home/andrew/.cargo/registry/src/github.aaakk.us.kg-1ecc6299db9ec823/regex-1.7.1/src/exec.rs:702:28

Thus, while the panic is originating inside the regex library, the panic comes from providing an invalid offset in the first place. This isn't an issue with the regex library.

[BurntSushi]

In the future, when reporting a bug, please provide a program that looks more like this:

fn main() {
    let pattern = "\0 \0\0\0\u{14};:;;\u{1}\u{1b}:D;J[;;;--]";
    let haystack = "/;*\u{1f}]/\u{1b}:;---\u{1b}:;;;;<;;;:\0";
    let at = 16607023625928704;
    let re = regex::Regex::new(pattern).unwrap();
    let result = re.shortest_match_at(haystack, at);
    dbg!(result);
}

This makes it much clearer what's going on and that the fault lies with the input. Your submission instead contains what looks like auto-generated code and the actual relevant input parameters are not clear.

[bhao-Soo]

Thank you very much for your timely reply. I have understood the reason, and I will make improvements to your suggestions.