On Thu, Oct 01, 2020 at 05:46:25PM +0100, Andre Przywara wrote:
> With -Wsign-compare, compilers warn about a mismatching signedness
> in a comparison in fdt_add_string_().
>
> Make all variables unsigned, and express the negative offset trick via
> subtractions in the code.
>
> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
Applied. I think there are some followup improvements we could make
here, though.
> ---
> libfdt/fdt_sw.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/libfdt/fdt_sw.c b/libfdt/fdt_sw.c
> index 8de18fd..354f466 100644
> --- a/libfdt/fdt_sw.c
> +++ b/libfdt/fdt_sw.c
> @@ -250,18 +250,18 @@ int fdt_end_node(void *fdt)
> static int fdt_add_string_(void *fdt, const char *s)
> {
> char *strtab = (char *)fdt + fdt_totalsize(fdt);
> - int strtabsize = fdt_size_dt_strings(fdt);
> - int len = strlen(s) + 1;
> - int struct_top, offset;
> + unsigned int strtabsize = fdt_size_dt_strings(fdt);
> + unsigned int len = strlen(s) + 1;
In both the old and new versions, there's an implicit cast from size_t
here, which I think could theoretically overflow (with a colossal
string, 32-bit ints and 64-bit pointers/size_t). So we probably
should actually check that this is <= INT_MAX.
> + unsigned int struct_top, offset;
>
> - offset = -strtabsize - len;
> + offset = strtabsize + len;
> struct_top = fdt_off_dt_struct(fdt) + fdt_size_dt_struct(fdt);
> - if (fdt_totalsize(fdt) + offset < struct_top)
> + if (fdt_totalsize(fdt) - offset < struct_top)
Likewise we should check that totalisize - offset doesn't overflow
(underflow?).
> return 0; /* no more room :( */
>
> - memcpy(strtab + offset, s, len);
> + memcpy(strtab - offset, s, len);
> fdt_set_size_dt_strings(fdt, strtabsize + len);
> - return offset;
> + return -offset;
> }
>
> /* Must only be used to roll back in case of error */
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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