Re: [PATCH] tap-win32: fix format-truncation warning

[Alex Bennée]

Pierrick Bouvier <pierrick.bouvier@linaro.org> writes:

> Simply increase destination buffer size so truncation can't happen.
>
> "cc" "-m64" "-Ilibcommon.a.p" "-Isubprojects/dtc/libfdt"
> "-I../subprojects/dtc/libfdt"
> "-ID:/a/_temp/msys64/mingw64/include/pixman-1"
> "-ID:/a/_temp/msys64/mingw64/include/glib-2.0"
> "-ID:/a/_temp/msys64/mingw64/lib/glib-2.0/include"
> "-ID:/a/_temp/msys64/mingw64/include/ncursesw"
> "-fdiagnostics-color=auto" "-Wall" "-Winvalid-pch" "-Werror"
> "-std=gnu11" "-O2" "-g" "-fstack-protector-strong" "-Wempty-body"
> "-Wendif-labels" "-Wexpansion-to-defined" "-Wformat-security"
> "-Wformat-y2k" "-Wignored-qualifiers" "-Wimplicit-fallthrough=2"
> "-Winit-self" "-Wmissing-format-attribute" "-Wmissing-prototypes"
> "-Wnested-externs" "-Wold-style-declaration" "-Wold-style-definition"
> "-Wredundant-decls" "-Wshadow=local" "-Wstrict-prototypes"
> "-Wtype-limits" "-Wundef" "-Wvla" "-Wwrite-strings"
> "-Wno-missing-include-dirs" "-Wno-psabi" "-Wno-shift-negative-value"
> "-iquote" "." "-iquote" "D:/a/qemu/qemu" "-iquote"
> "D:/a/qemu/qemu/include" "-iquote"
> "D:/a/qemu/qemu/host/include/x86_64" "-iquote"
> "D:/a/qemu/qemu/host/include/generic" "-iq
> ../net/tap-win32.c: In function 'tap_win32_open':
> ../net/tap-win32.c:343:19: error: '%s' directive output may be truncated 
> writing up to 255 bytes into a region of size 176 [-Werror=format-truncation=]
>   343 |              "%s\\%s\\Connection",
>       |                   ^~
>   344 |              NETWORK_CONNECTIONS_KEY, enum_name);
>       |                                       ~~~~~~~~~
> In function 'get_device_guid',
>     inlined from 'tap_win32_open' at ../net/tap-win32.c:616:10:
> ../net/tap-win32.c:341:9: note: 'snprintf' output between 92 and 347
> bytes into a destination of size 256

Is the compiler min/max maxing what UCS-16 or UTF-8 might pack into that string?
>
> Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
> ---
>  net/tap-win32.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/net/tap-win32.c b/net/tap-win32.c
> index 7edbd716337..4a4625af2b2 100644
> --- a/net/tap-win32.c
> +++ b/net/tap-win32.c
> @@ -214,7 +214,7 @@ static int is_tap_win32_dev(const char *guid)
>  
>      for (;;) {
>          char enum_name[256];
> -        char unit_string[256];
> +        char unit_string[512];

If this isn't perf sensitive code lets just get rid of this stack
allocation and be done with some autofree'd g_strdup_printfs?

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro