[PATCH v3] ash: fix out-of-bounds read in ifsbreakup()

[Sanghyun Park]

Hi Denys,

Thanks for applying it.

Here's my reproducer for this bug:

base64 -d > poc.sh <<'EOF'
IyEvYmJiAS0tIGE6YjpjCmVjZSA8PCB2Yf+AYWJsZSBhbmQ7YUVPRgpoZW4KRU9cCmVjaG8AJC0tLS0tLS0tYjpjCiR7XzooKDdiACByZWEtLS1iOmMKJQskJCQIJCQkCCQkI3t9Ch0/Yw==
EOF

You could reproduce it with ASAN as follows:
ASAN_OPTIONS=detect_leaks=0:abort_on_error=1:halt_on_error=1 ./busybox ash ./poc.sh

On my pre-patch BusyBox v1.38.0.git build with ASAN, this reports:

ERROR: AddressSanitizer: heap-buffer-overflow 
READ of size 1 
#0 ifsbreakup

Cheers,
Sanghyun