[Bug 7688] New: ash: segmentation fault with substring at negative offset

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=7688

           Summary: ash: segmentation fault with substring at negative
                    offset
           Product: Busybox
           Version: 1.22.x
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: major
          Priority: P5
         Component: Other
        AssignedTo: unassigned at busybox.net
        ReportedBy: ronald.wahl at raritan.com
                CC: busybox-cvs at busybox.net
   Estimated Hours: 0.0


The following command line will crash ash:

a=;echo ${a:$((0-8192))}

It looks like that there is no sanity check for negative offsets. Furthermore
bash looks at the string from behind when using negative offsets. This would be
a cool feature. Currently I have to fiddle around to achieve this and the above
segmentation fault was the fall-out of my testing.

I tested with 1.21.1 and 1.22.1 both show the issue. Others not checked.

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