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mrb_str_modify tries to write to static string #3373

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clayton-shopify opened this Issue Jan 5, 2017 · 0 comments

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clayton-shopify commented Jan 5, 2017

The following code demonstrates a crash:

a = Time.new.zone # allocates static string
a[0] # converts to shared string
GC.start # reduces refcnt to 1?
a.next! #crash

The crash occurs here, where an attempt is made to write to a static string's buffer (which is not writeable):

RSTR_PTR(s)[s->as.heap.len] = '\0';

The crash is not particular to Time#zone; the first line can be changed to anything that allocates a static string, e.g. a = :a.to_s.

I haven't investigated further, so I'm not sure what the right fix is.

This issue was reported by https://hackerone.com/marotagem_vrt

@matz matz closed this in f53f73f Jan 6, 2017

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