On Thu, Mar 05, 2020 at 03:04:45PM +0100, Jan Beulich wrote:
> libfdt: fix undefined behaviour in fdt_splice_()
>
> Along the lines of commit d0b3ab0a0f46 ("libfdt: Fix undefined behaviour
> in fdt_offset_ptr()"), fdt_splice_() similarly may not use pointer
> arithmetic to do overflow checks. (The left side of the checks added by
> d4c7c25c9ed1 ["libfdt: check for potential overrun in _fdt_splice()"]
> doesn't really lend itself to similar replacement though.)
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Applied, thanks.
> ---
> The right side of the checks added by d4c7c25c9ed1 looks suspicious,
> which is more noticable after the transformation done here:
>
> end - oldlen + newlen < (char *)fdt
>
> end - (char *)fdt + newlen < oldlen
>
> dsize + newlen < oldlen
Hrm, yeah, I think this is trying to check for overflow of
dsize+newlen, but it's pretty hard to follow.
>
> --- a/libfdt/fdt_rw.c
> +++ b/libfdt/fdt_rw.c
> @@ -46,7 +46,7 @@ static int fdt_rw_probe_(void *fdt)
> return err_; \
> }
>
> -static inline int fdt_data_size_(void *fdt)
> +static inline unsigned int fdt_data_size_(void *fdt)
> {
> return fdt_off_dt_strings(fdt) + fdt_size_dt_strings(fdt);
> }
> @@ -54,15 +54,16 @@ static inline int fdt_data_size_(void *f
> static int fdt_splice_(void *fdt, void *splicepoint, int oldlen, int newlen)
> {
> char *p = splicepoint;
> - char *end = (char *)fdt + fdt_data_size_(fdt);
> + unsigned int dsize = fdt_data_size_(fdt);
> + size_t soff = p - (char *)fdt;
>
> - if (((p + oldlen) < p) || ((p + oldlen) > end))
> + if ((oldlen < 0) || (soff + oldlen < soff) || (soff + oldlen > dsize))
> return -FDT_ERR_BADOFFSET;
> - if ((p < (char *)fdt) || ((end - oldlen + newlen) < (char *)fdt))
> + if ((p < (char *)fdt) || (dsize + newlen < oldlen))
> return -FDT_ERR_BADOFFSET;
> - if ((end - oldlen + newlen) > ((char *)fdt + fdt_totalsize(fdt)))
> + if (dsize - oldlen + newlen > fdt_totalsize(fdt))
> return -FDT_ERR_NOSPACE;
> - memmove(p + newlen, p + oldlen, end - p - oldlen);
> + memmove(p + newlen, p + oldlen, ((char *)fdt + dsize) - (p + oldlen));
> return 0;
> }
>
>
--
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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