[Bug 1712253] Re: swprintf does not guarantee NUL termination
James Lin
1712253 at bugs.launchpad.net
Wed Jan 23 23:33:07 UTC 2019
This still occurs with glibc 2.27-3ubuntu1 from Ubuntu 18.04.1 LTS x64.
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https://bugs.launchpad.net/bugs/1712253
Title:
swprintf does not guarantee NUL termination
Status in glibc package in Ubuntu:
New
Bug description:
The C99 specification states for swprintf (section 7.24.2.3):
> The swprintf function is equivalent to fwprintf, except that the
argument s specifies an array of wide characters into which the
generated output is to be written, rather than written to a stream. No
more than n wide characters are written, including a terminating null
wide character, which is always added (unless n is zero).
My interpretation that "always" includes failure, including truncation
error. However, it appears that swprintf from glibc does NOT NUL-
terminate on truncation. (I am using glibc 2.24 and gcc 6.3.0 20170406
from an Ubuntu 17.04 x64 (desktop) live CD.)
I have attached sample code that exhibits this problem. The output I
expect is:
ret: -1 buf: 68 0
but instead I get:
ret: -1 buf: 68 cacacaca
(I do get the expected behavior with libc on FreeBSD and macOS.)
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