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http://bugs.gentoo.org/213833
commit 913c09becd9df89dbd9b9f386e7f35c240d5efe8
Author: Bruno Haible <bruno@clisp.org>
Date: Fri Oct 19 01:50:42 2007 +0200
Don't use %n on glibc >= 2.3 systems.
diff --git a/lib/vasnprintf.c b/lib/vasnprintf.c
index f563823..5d818aa 100644
--- a/lib/vasnprintf.c
+++ b/lib/vasnprintf.c
@@ -3385,9 +3385,21 @@ VASNPRINTF (DCHAR_T *resultbuf, size_t *lengthp,
#endif
*fbp = dp->conversion;
#if USE_SNPRINTF
+# if !(__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 3))
fbp[1] = '%';
fbp[2] = 'n';
fbp[3] = '\0';
+# else
+ /* On glibc2 systems from glibc >= 2.3 - probably also older
+ ones - we know that snprintf's returns value conforms to
+ ISO C 99: the gl_SNPRINTF_DIRECTIVE_N test passes.
+ Therefore we can avoid using %n in this situation.
+ On glibc2 systems from 2004-10-18 or newer, the use of %n
+ in format strings in writable memory may crash the program
+ (if compiled with _FORTIFY_SOURCE=2), so we should avoid it
+ in this situation. */
+ fbp[1] = '\0';
+# endif
#else
fbp[1] = '\0';
#endif
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