[tor-bugs] #9066 [Tor]: use a macro like CHECK_PRINTF for tor_sscanf

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#9066: use a macro like CHECK_PRINTF for tor_sscanf
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 Reporter:  x3j11   |          Owner:                     
     Type:  defect  |         Status:  new                
 Priority:  normal  |      Milestone:  Tor: 0.2.5.x-final 
Component:  Tor     |        Version:  Tor: 0.2.4.12-alpha
 Keywords:          |         Parent:                     
   Points:          |   Actualpoints:                     
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Comment(by andrea):

 The particular test in question appears to be an OpenBSD-specific
 extension; an examination of gcc/c-family/c-format.c in the latest
 gcc-4.8.1, where the __attribute(format())__ warnings are implemented,
 shows no sign of checking string argument widths, and grepping the source
 for 'format string size' turns up negative.

 I'll also note that in the particular instance reported in test_util.c,
 the function actually is provably safe, since the string being sscanf()ed
 is shorter than the buffer even though the field precision in the format
 string is longer.  This is a case of a modified gcc implementing a
 stricter test than standard gcc, but not precisely enough to notice that
 the particular instance is safe.

 I do not believe it would be possible for a compiler to support doing this
 test in a way that would recognize this, though, since
 __attribute(format(scanf,...))__ only tells the compiler which is the
 format string and where the formatted arg sequence starts.  There's no way
 for it know this is an sscanf()-alike more specifically and which is the
 input string, and reason from there even if the input string is a constant
 which would make it possible to draw that conclusion if it did know.

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/9066#comment:5>
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