date -f / is doing an infinite loop on Is a directory

[sylvestre]

Found with the fuzzer introduced in #4389

target/debug/coreutils date -f /
runs forever.

strace shows

read(3, 0x561efbdd70e0, 8192)           = -1 EISDIR (Is a directory)
read(3, 0x561efbdd70e0, 8192)           = -1 EISDIR (Is a directory)
read(3, 0x561efbdd70e0, 8192)           = -1 EISDIR (Is a directory)

while date -f / on GNU returns immediately without any message (which might be a bug)

[shanmukhateja]

@sylvestre I'd like to give this a try.

[tertsdiepraam]

This seems to be due to the .lines() call and the next calls on it. It honestly feels like bug in the standard library (or at the very least a pitfall).

[tertsdiepraam]

This issue is related: rust-lang/rust#64144 (but they seem reluctant to change the behaviour)

[shanmukhateja]

Yes, I agree. It is definitely related to Files not returning when accessing a directory.

[tertsdiepraam]

We should probably check our entire codebase for this, basically every time we call BufReader::lines() this issue could be present.

[tertsdiepraam]

Okay, I actually don't think this is a footgun anymore. The problem is actually on our side, because we explicitly ignore the errors, which obviously doesn't get us the right behaviour. This would fix it for instance:

             DateSource::File(ref path) => {
                 file = File::open(path).unwrap();
                 let lines = BufReader::new(file).lines();
-                let iter = lines.filter_map(Result::ok).map(parse_date);
+                let iter = lines.map_while(Result::ok).map(parse_date);
                 Box::new(iter)
             }
             DateSource::Now => {

@shanmukhateja feel free to incorporate this in your PR.