Date: Sat, 05 Nov 2022 07:52:09 -0400 From: "Alex Xu (Hello71)" <alex_y_xu@...oo.ca> To: Szabolcs Nagy <nsz@...t70.net>, musl@...ts.openwall.com, Markus Wichmann <nullplan@....net> Subject: Re: Invalid read of nl_arg in printf_core() Excerpts from Szabolcs Nagy's message of November 5, 2022 6:09 am: > * Markus Wichmann <nullplan@....net> [2022-11-03 20:42:16 +0100]: >> Hi all, >> >> reading some code today, I noticed undefined behavior in printf_core(). >> vfprintf() creates an array called nl_arg automatically and does not >> initialize it. That is fine, but it means that reads from each array >> member are undefined behavior until that member gets assigned a value. > > an automatic storage object that was not initialized has indeterminate > value, so accessing it is not undefined behaviour. (unless the object > could have been declared with the register storage class) > > so technically the code is correct (if int has no trap representations) > but i think the fix still makes sense: leaving unspecified values around > is error prone. N1570 J.2 [Undefined behavior]: 1 The behavior is undefined in the following circumstances: [ ... ] — The value of an object with automatic storage duration is used while it is indeterminate (6.2.4, 6.7.9, 6.8).
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