On 14.11.24 16:51, Abdelrahman Youssef wrote:
> While fuzzing, the name marked by FDT_BEGIN_NODE sometimes extends beyond
> the struct block area, causing a heap-overflow.
>
> Since `maxlen` is an unsigned integer representing the length of name,
> It can be negative, so it overflows to large numbers, Causing strnlen()
> to overflow.
>
> So we can just change the type of maxlen to signed and check if it's a
> non-positive value, because name has a minimum length of 1 byte ('\0').
>
> Also in strnlen() we shouldn't check for bytes exceeding maxlen, so we can remove
> + 1 in strnlen(). We also change if (len > maxlen) to >= to count for the null
> terminator.
>
> Signed-off-by: Abdelrahman Youssef <abdelrahmanyossef12@xxxxxxxxx>
Reviewed-by: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx>
>
> ---
> v3 -> v4:
> - replace maxlen < 0 to maxlen <= 0 (Sascha)
> - remove + 1 in strnlen() (Sascha)
> v2 -> v3
> - changed formatting
> v1 -> v2
> - the overflow was due to integer overflow not out-of-bounds (Ahmad)
> ---
> drivers/of/fdt.c | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> index 2c3ea31394..75af1844f3 100644
> --- a/drivers/of/fdt.c
> +++ b/drivers/of/fdt.c
> @@ -176,7 +176,7 @@ static struct device_node *__of_unflatten_dtb(const void *infdt, int size,
> void *dt_strings;
> struct fdt_header f;
> int ret;
> - unsigned int maxlen;
> + int maxlen;
> const struct fdt_header *fdt = infdt;
>
> ret = fdt_parse_header(infdt, size, &f);
> @@ -210,8 +210,13 @@ static struct device_node *__of_unflatten_dtb(const void *infdt, int size,
> maxlen = (unsigned long)fdt + f.off_dt_struct +
> f.size_dt_struct - (unsigned long)name;
>
> - len = strnlen(name, maxlen + 1);
> - if (len > maxlen) {
> + if (maxlen <= 0) {
> + ret = -ESPIPE;
> + goto err;
> + }
> +
> + len = strnlen(name, maxlen);
> + if (len >= maxlen) {
> ret = -ESPIPE;
> goto err;
> }
--
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