[PATCH net] net/smc: fix limit_smc_hs sysctl on big-endian architecture

[PATCH net] net/smc: fix limit_smc_hs sysctl on big-endian architecture

[Fernando Fernandez Mancera]

net->smc.limit_smc_hs is a bool, but its sysctl entry uses
proc_dointvec_minmax() with .maxlen = sizeof(int), so the handler
accesses four bytes at the address of a one-byte field.

On little-endian this works with the extra bytes being written in struct
padding. On big-endian (tested on s390x) the bool sits at the most
significant byte of the int therefore the bool stays false and the "1"
goes into padding. The sysctl reads back 1 but SMC sockets created
afterwards see limit_smc_hs as disabled.

Fix this by using proc_dobool() handler and adjust the maxlen to the
right value.

Fixes: f8406a2fd279 ("net/smc: add sysctl for smc_limit_hs")
Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
---
Note: After reviewing another patch fixing sysctls, I decided to
review more of them and found this. I have tested the fix on a s390x
system.
---
 net/smc/smc_sysctl.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/net/smc/smc_sysctl.c b/net/smc/smc_sysctl.c
index 09dad48337f6..f58cf256f61a 100644
--- a/net/smc/smc_sysctl.c
+++ b/net/smc/smc_sysctl.c
@@ -160,11 +160,9 @@ static const struct ctl_table smc_table[] = {
 	{
 		.procname	= "limit_smc_hs",
 		.data		= &init_net.smc.limit_smc_hs,
-		.maxlen		= sizeof(int),
+		.maxlen		= sizeof(bool),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= SYSCTL_ZERO,
-		.extra2		= SYSCTL_ONE,
+		.proc_handler	= proc_dobool,
 	},
 	{
 		.procname	= "smcr_max_send_wr",
-- 
2.56.0

Re: [PATCH net] net/smc: fix limit_smc_hs sysctl on big-endian architecture

[sashiko-bot]

> net->smc.limit_smc_hs is a bool, but its sysctl entry uses
> proc_dointvec_minmax() with .maxlen = sizeof(int), so the handler
> accesses four bytes at the address of a one-byte field.
> 
> On little-endian this works with the extra bytes being written in struct
> padding. On big-endian (tested on s390x) the bool sits at the most
> significant byte of the int therefore the bool stays false and the "1"
> goes into padding. The sysctl reads back 1 but SMC sockets created
> afterwards see limit_smc_hs as disabled.
> 
> Fix this by using proc_dobool() handler and adjust the maxlen to the
> right value.
> 
> Fixes: f8406a2fd279 ("net/smc: add sysctl for smc_limit_hs")
> Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>

Sashiko has reviewed this patch and found no issues.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261028225350.3753-1-fmancera@suse.de?part=1