| Message ID | 20180307230714.GA20797@beast (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Kees, On Wed, Mar 07, 2018 at 03:07:14PM -0800, Kees Cook wrote: > The "sym" calculation is actually a fixed size, but since the max() > macro uses some extensive tricks for safety, it ends up looking like a > variable size. This replaces max() with a simple max macro which is > sufficient for the calculation of the array size. > > Seen with -Wvla. Fixed as part of the directive to remove all VLAs from > the kernel: https://lkml.org/lkml/2018/3/7/621 > > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > lib/vsprintf.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c > index d7a708f82559..f420ab1477cb 100644 > --- a/lib/vsprintf.c > +++ b/lib/vsprintf.c > @@ -744,8 +744,9 @@ char *resource_string(char *buf, char *end, struct resource *res, > #define FLAG_BUF_SIZE (2 * sizeof(res->flags)) > #define DECODED_BUF_SIZE sizeof("[mem - 64bit pref window disabled]") > #define RAW_BUF_SIZE sizeof("[mem - flags 0x]") > - char sym[max(2*RSRC_BUF_SIZE + DECODED_BUF_SIZE, > - 2*RSRC_BUF_SIZE + FLAG_BUF_SIZE + RAW_BUF_SIZE)]; > +#define SIMPLE_MAX(x, y) ((x) > (y) ? (x) : (y)) It's probably worth hoisting this out into some other header. When I was looking at this a while ago, this problem happens in a few places, see e.g. net/ipv4/proc.c:TCPUDP_MIB_MAX. Cheers, Tycho
On Wed, Mar 7, 2018 at 3:42 PM, Tycho Andersen <tycho@tycho.ws> wrote: > Hi Kees, > > On Wed, Mar 07, 2018 at 03:07:14PM -0800, Kees Cook wrote: >> The "sym" calculation is actually a fixed size, but since the max() >> macro uses some extensive tricks for safety, it ends up looking like a >> variable size. This replaces max() with a simple max macro which is >> sufficient for the calculation of the array size. >> >> Seen with -Wvla. Fixed as part of the directive to remove all VLAs from >> the kernel: https://lkml.org/lkml/2018/3/7/621 >> >> Signed-off-by: Kees Cook <keescook@chromium.org> >> --- >> lib/vsprintf.c | 5 +++-- >> 1 file changed, 3 insertions(+), 2 deletions(-) >> >> diff --git a/lib/vsprintf.c b/lib/vsprintf.c >> index d7a708f82559..f420ab1477cb 100644 >> --- a/lib/vsprintf.c >> +++ b/lib/vsprintf.c >> @@ -744,8 +744,9 @@ char *resource_string(char *buf, char *end, struct resource *res, >> #define FLAG_BUF_SIZE (2 * sizeof(res->flags)) >> #define DECODED_BUF_SIZE sizeof("[mem - 64bit pref window disabled]") >> #define RAW_BUF_SIZE sizeof("[mem - flags 0x]") >> - char sym[max(2*RSRC_BUF_SIZE + DECODED_BUF_SIZE, >> - 2*RSRC_BUF_SIZE + FLAG_BUF_SIZE + RAW_BUF_SIZE)]; >> +#define SIMPLE_MAX(x, y) ((x) > (y) ? (x) : (y)) > > It's probably worth hoisting this out into some other header. When I > was looking at this a while ago, this problem happens in a few places, > see e.g. net/ipv4/proc.c:TCPUDP_MIB_MAX. Hmm, good point. All of those suffer from the same "max*() is too fancy". I didn't want to encourage a global macro that _lacked_ the safety built into the max*() family, though... thoughts for a reasonable approach? -Kees
On Wed, 7 Mar 2018 15:59:27 -0800 Kees Cook <keescook@chromium.org> wrote: > I didn't want to encourage a global macro that _lacked_ the safety > built into the max*() family, though... thoughts for a reasonable > approach? I think SIMPLE_MAX() is OK. Along with one of /* these */ things ;)
On Wed, Mar 7, 2018 at 4:03 PM, Andrew Morton <akpm@linux-foundation.org> wrote: > On Wed, 7 Mar 2018 15:59:27 -0800 Kees Cook <keescook@chromium.org> wrote: > >> I didn't want to encourage a global macro that _lacked_ the safety >> built into the max*() family, though... thoughts for a reasonable >> approach? > > I think SIMPLE_MAX() is OK. Along with one of /* these */ things ;) Sounds good. I will resend with net/ipv[46]/proc.c and one other fixed as well... -Kees
diff --git a/lib/vsprintf.c b/lib/vsprintf.c index d7a708f82559..f420ab1477cb 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -744,8 +744,9 @@ char *resource_string(char *buf, char *end, struct resource *res, #define FLAG_BUF_SIZE (2 * sizeof(res->flags)) #define DECODED_BUF_SIZE sizeof("[mem - 64bit pref window disabled]") #define RAW_BUF_SIZE sizeof("[mem - flags 0x]") - char sym[max(2*RSRC_BUF_SIZE + DECODED_BUF_SIZE, - 2*RSRC_BUF_SIZE + FLAG_BUF_SIZE + RAW_BUF_SIZE)]; +#define SIMPLE_MAX(x, y) ((x) > (y) ? (x) : (y)) + char sym[SIMPLE_MAX(2*RSRC_BUF_SIZE + DECODED_BUF_SIZE, + 2*RSRC_BUF_SIZE + FLAG_BUF_SIZE + RAW_BUF_SIZE)]; char *p = sym, *pend = sym + sizeof(sym); int decode = (fmt[0] == 'R') ? 1 : 0;
The "sym" calculation is actually a fixed size, but since the max() macro uses some extensive tricks for safety, it ends up looking like a variable size. This replaces max() with a simple max macro which is sufficient for the calculation of the array size. Seen with -Wvla. Fixed as part of the directive to remove all VLAs from the kernel: https://lkml.org/lkml/2018/3/7/621 Signed-off-by: Kees Cook <keescook@chromium.org> --- lib/vsprintf.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)