Re: [PATCH 1/2] sysctl: Negate before converting in the int read path

[Joel Granados]

On Tue, Sep 22, 2026 at 07:37:57AM +0100, Bradley Morgan wrote:
> On 22 September 2026 04:12:27 BST, Zhan Xusheng <zhanxusheng1024@xxxxxxxxx>
> wrote:
> >proc_int_k2u_conv_kop() reports the sign through *negp and the magnitude
> >through *u_ptr, but for a negative value it hands the sign-extended int to
> >the converter and negates the result:
> >
> >	*u_ptr = k_ptr_op ? -k_ptr_op((ulong)val) : -(ulong)val;
> >
> >With div_hz() and HZ=1000 a stored -1000 becomes
> >(ulong)-1000 / 1000 == 18446744073709550, and negating that wraps:
> >
> >	# echo -1 > /proc/sys/net/ipv4/tcp_fin_timeout
> >	# cat /proc/sys/net/ipv4/tcp_fin_timeout
> >	-18428297329635842066
> >
> >Take the magnitude first and convert that, which is what the open-coded
> >version did before commit 2dc164a48e6f ("sysctl: Create converter
> >functions with two new macros") folded it into a macro.  The
> >k_ptr_op == NULL branch was already correct.
> >
> >proc_dointvec_jiffies() and proc_dointvec_ms_jiffies() are affected.
> >
> >Fixes: 2dc164a48e6f ("sysctl: Create converter functions with two new macros")
> >Cc: stable@xxxxxxxxxxxxxxx
> >Signed-off-by: Zhan Xusheng <zhanxusheng@xxxxxxxxxx>
> >---
> > kernel/sysctl.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> >diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> >index f7b75985d542..38597f26b34c 100644
> >--- a/kernel/sysctl.c
> >+++ b/kernel/sysctl.c
> >@@ -483,7 +483,7 @@ int proc_int_k2u_conv_kop(ulong *u_ptr, const int *k_ptr, bool *negp,
> > 
> > 	if (val < 0) {
> > 		*negp = true;
> >-		*u_ptr = k_ptr_op ? -k_ptr_op((ulong)val) : -(ulong)val;
> >+		*u_ptr = k_ptr_op ? k_ptr_op(-(ulong)val) : -(ulong)val;
> > 	} else {
> > 		*negp = false;
> > 		*u_ptr = k_ptr_op ? k_ptr_op((ulong)val) : (ulong) val;
> >
> I didn't do much crazy review here, but I think this LGTM! :)

If you didn't do much, please don't send the mail.

> 
> Reviewed-by: Bradley Morgan <brads@xxxxxxxxxxxxxx>
> 
> --- Thanks!
> "I'm not a very positive person" - Linus torvalds

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