[PATCH] fsi: i2cr-scom: Return -EFAULT on usercopy failures

[PATCH] fsi: i2cr-scom: Return -EFAULT on usercopy failures

[Karl Mehltretter]

copy_to_user() and copy_from_user() return the number of bytes that were
not copied. i2cr_scom_read() and i2cr_scom_write() return that value
directly, so a usercopy fault is reported as a successful short I/O.

Return -EFAULT when either copy fails.

A temporary KUnit test called i2cr_scom_write() with an invalid user
pointer. The unmodified kernel returned 8. With this change it returned
-EFAULT. Both versions were booted under QEMU.

Fixes: c0b34bed0bbf ("fsi: Add I2C Responder SCOM driver")
Assisted-by: LLM
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
---
 drivers/fsi/i2cr-scom.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/fsi/i2cr-scom.c b/drivers/fsi/i2cr-scom.c
index 83b3c03..7edd3e5 100644
--- a/drivers/fsi/i2cr-scom.c
+++ b/drivers/fsi/i2cr-scom.c
@@ -46,7 +46,7 @@ static ssize_t i2cr_scom_read(struct file *filep, char __user *buf, size_t len,
 
 	ret = copy_to_user(buf, &data, len);
 	if (ret)
-		return ret;
+		return -EFAULT;
 
 	return len;
 }
@@ -63,7 +63,7 @@ static ssize_t i2cr_scom_write(struct file *filep, const char __user *buf, size_
 
 	ret = copy_from_user(&data, buf, len);
 	if (ret)
-		return ret;
+		return -EFAULT;
 
 	ret = fsi_master_i2cr_write(scom->i2cr, (u32)*offset, data);
 	if (ret)

base-commit: 22098763a10d9c1340827fcf6edab66f153b27f0
-- 
2.53.0

Re: [PATCH] fsi: i2cr-scom: Return -EFAULT on usercopy failures

[Karl Mehltretter]

On Mon, Sep 14, 2026 at 08:24:26AM +0100, Karl Mehltretter wrote:
> copy_to_user() and copy_from_user() return the number of bytes that were
> not copied. i2cr_scom_read() and i2cr_scom_write() return that value
> directly, so a usercopy fault is reported as a successful short I/O.
> 
> Return -EFAULT when either copy fails.
> 
> A temporary KUnit test called i2cr_scom_write() with an invalid user
> pointer. The unmodified kernel returned 8. With this change it returned
> -EFAULT. Both versions were booted under QEMU.
> 
> Fixes: c0b34bed0bbf ("fsi: Add I2C Responder SCOM driver")
> Assisted-by: LLM
> Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>

A friendly ping on this usercopy error-handling fix.

Thanks,
Karl