Fwd: [PATCH 3/3] sysctl: detect overflows when converting to int

[Heinrich Schuchardt <xypron.glpk@gmx.de>]

Hello Andrew,

could you, please, propagate the patch in
https://lkml.org/lkml/2015/3/29/189
to the MM tree.

It is independent of the other two patches in the patch series.
Rework for the other patches was requested by Alexey Dobriyan in
https://lkml.org/lkml/2015/3/31/251

Best regards

Heinrich Schuchardt

On 29.03.2015 21:28, Heinrich Schuchardt wrote:
> When converting unsigned long to int overflows may occur.
> These currently are not detected when writing to the sysctl
> file system.
> 
> E.g. on a system where int has 32 bits and long has 64 bits
>   echo 0x800001234 > /proc/sys/kernel/threads-max
> has the same effect as
>   echo 0x1234 > /proc/sys/kernel/threads-max
> 
> The patch adds the missing check in do_proc_dointvec_conv.
> 
> With the patch an overflow will result in an error EINVAL when
> writing to the the sysctl file system.
> 
> Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
> ---
>  kernel/sysctl.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index 4d9d139..2fd6b82 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1953,7 +1953,15 @@ static int do_proc_dointvec_conv(bool *negp, unsigned long *lvalp,
>  				 int write, void *data)
>  {
>  	if (write) {
> -		*valp = *negp ? -*lvalp : *lvalp;
> +		if (*negp) {
> +			if (*lvalp > (unsigned long) INT_MAX + 1)
> +				return -EINVAL;
> +			*valp = -*lvalp;
> +		} else {
> +			if (*lvalp > (unsigned long) INT_MAX)
> +				return -EINVAL;
> +			*valp = *lvalp;
> +		}
>  	} else {
>  		int val = *valp;
>  		if (val < 0) {
>