fuzzing Running test ["seq", "-49.450798063728875", "3458"] is staled

[sylvestre]

cargo +nightly fuzz run fuzz_seq -- -max_total_time=600 -detect_leaks=0
freeze on:
Running test ["seq", "-49.450798063728875", "3458"]
rust-gdb -p shows that it is on:
write!(stdout, "{separator}")?;

coreutils/src/uu/seq/src/seq.rs

Line 220 in 052f38f

write!(stdout, "{separator}")?;

i don't know what is going on ?!

[samueltardieu]

It looks like fuzz_common::generate_and_run_uumain() in the fuzzing framework sets up pipes for stdout/stderr and reads them afterwards. However, the default pipe size on Linux is 16 pages, i.e. 64kiB on most systems. The output of seq -49.450798063728875 3458 is more than 70kiB, so the write size of the pipe will block until the pipe is read from, which never happens before the command completes.

I can see at least two ways to fix this:

• limit the command output/error to 64kiB in any case
• use two separate threads, one for running the command and one for reading its output