Hi Lianbo,
On Mon, 27 Sep 2021 11:33:31 +0800
lijiang <lijiang@xxxxxxxxxx> wrote:
> > Date: Sat, 18 Sep 2021 15:59:30 +0800
> > From: Tao Liu <ltao@xxxxxxxxxx>
> > To: crash-utility@xxxxxxxxxx
> > Subject: [PATCH v4 2/4] Get the absolute value of
> > SYMNAME_HASH_INDEX
> > Message-ID: <20210918075932.132339-3-ltao@xxxxxxxxxx>
> > Content-Type: text/plain; charset="US-ASCII"
> >
> > SYMNAME_HASH_INDEX is used as the index of symname hash table. It will
> > be out of range if SYMNAME_HASH_INDEX is negative. Let's get its absolute
> > value to avoid such risk.
> >
> > Signed-off-by: Tao Liu <ltao@xxxxxxxxxx>
> > Reviewed-by: Philipp Rudo <prudo@xxxxxxxxxx>
> > ---
> > defs.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/defs.h b/defs.h
> > index c10ebff..3129f06 100644
> > --- a/defs.h
> > +++ b/defs.h
> > @@ -2725,7 +2725,7 @@ struct downsized {
> >
> > #define SYMNAME_HASH (512)
> > #define SYMNAME_HASH_INDEX(name) \
> > - ((name[0] ^ (name[strlen(name)-1] * name[strlen(name)/2])) % SYMNAME_HASH)
> > + (abs((name[0] ^ (name[strlen(name)-1] * name[strlen(name)/2])) % SYMNAME_HASH))
> >
>
> I guess this may be caused by integer overflow, the expression uses
> integer calculations by default. Does the following change work for
> you?
>
> -#define SYMNAME_HASH (512)
> +#define SYMNAME_HASH (512ULL)
the above isn't sufficient. The sign of the result is defined by the
sign of the dividend, i.e. assume a % b, then the result has the same
sign as a. So the result of SYMNAME_HASH_INDEX will become negative
whenever
name[0] ^ (name[strlen(name)-1] * name[strlen(name)/2])
is negative. So the only alternative I see is to guarantee that 'name'
is an unsigned char. But that would be more complicated to implement
then simply adding the 'abs'.
Thanks
Philipp
>
> Thanks.
> Lianbo
> > #define PATCH_KERNEL_SYMBOLS_START ((char *)(1))
> > #define PATCH_KERNEL_SYMBOLS_STOP ((char *)(2))
> > --
> > 2.29.2
> >
>
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