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try to enforce use of anchors, ^ and/ or $


Am 11.06.20 um 17:03 schrieb
The string package has regular expression matching, and they can be used to leverage Check the following example, which takes 25 seconds to run.

start = os.time()
s = string.gsub('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa', 'a*a*a*a*a*a*a*b', 'X')
print('ran in ', os.difftime(os.time(), start), ' second(s)')

I'd like to find a way to prevent from such "attack" on a system that would execute user provided lua scripts. The system uses a custom allocator that limits the memory that can be allocated, and a hook that calls lua_error at next instruction executed if script evaluation takes too long.

Unfortunately, none of those help, because the above code doesn't need a lot of memory allocated to run, and the debug hook sees the whole gsub call as one instructions.

So the only solution I see is to not expose string.gsub() to users, or to run in a sandbox that can be terminated violently after some time. Has the Lua community figured out a better solution? Have I missed something in our hooks should be used, or potential native Lua ways of "bounding" execution?