https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111102
Bug ID: 111102
Summary: illegal pointer arithmetic invoked by
std::format("L{:65536}",1)
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: gcc at pauldreik dot se
Target Milestone: ---
The following program:
#include <format>
constexpr auto blah = std::format(L"{:65536}", 1);
is problematic when compiled with gcc 13 as well as the current trunk.
It triggers a pointer arithmetic error inside
https://gcc.gnu.org/git/?p=gcc.git;a=blame;f=libstdc%2B%2B-v3/include/std/format;hb=1d9454aba615eadd0d85c93713dd848227345f67#l295
it seems like the width is parsed into a unsigned short, but the return value
is not checked in the case the format string was not a char string (as above,
which is a wide char string).
The following patch fixes the problem:
commit 78ac41590432f4f01036797fd9d661f6ed80cf37 (HEAD -> master)
Author: Paul Dreik <[email protected]>
Date: Tue Aug 22 19:16:57 2023 +0200
libstdc++: fix illegal pointer arithmetic in format
when parsing a format string, the width is parsed into an unsigned short
but the result is not checked in the case the format string is not a
char string (such as a wide string). in case the parse fails,
a null pointer is returned which is used for pointer arithmetic
which is undefined behaviour.
Signed-off-by: Paul Dreik <[email protected]>
diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format
index f3d9ae152f..fe2caa5868 100644
--- a/libstdc++-v3/include/std/format
+++ b/libstdc++-v3/include/std/format
@@ -285,7 +285,8 @@ namespace __format
for (int __i = 0; __i < __n && (__first + __i) != __last; ++__i)
__buf[__i] = __first[__i];
auto [__v, __ptr] = __format::__parse_integer(__buf, __buf + __n);
- return {__v, __first + (__ptr - __buf)};
+ if (__ptr) [[likely]]
+ return {__v, __first + (__ptr - __buf)};
}
return {0, nullptr};
}
