While report_error_write() checks that the provided buffer is at least
as large as the header struct, but not that it is large enough to
contain the report with the length claimed by report->length. If
user-space provides a short buffer, meaning a larger report->length than
the actually written payload, up to around 4K of kernel data from past
the kmalloc(len + 1) sized buffer allocated in kernfs_fop_write_iter()
will leak into the SCLP report.

However, as the entity processing the SCLP is privileged and able to
access at least the page including the report, this does not leak data
that entity could not access but it is still an out of bounds read and
a malformed error report that should be rejected.

Fixes: 368704a65be8 ("s390/pci: add report_error attribute")
Cc: stable@vger.kernel.org
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
---
Changes in v2:
- Changed subsystem prefix to s390/pci
- Added Fixes tag and Cc stable
- Improved commit message
- Link to v1: https://lore.kernel.org/r/20260805-fix_pci_sclp_length_check-v1-1-d125cb415bc3@linux.ibm.com
---
 arch/s390/pci/pci_sysfs.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/s390/pci/pci_sysfs.c b/arch/s390/pci/pci_sysfs.c
index d98d97df792a..bbb76113a4d0 100644
--- a/arch/s390/pci/pci_sysfs.c
+++ b/arch/s390/pci/pci_sysfs.c
@@ -153,6 +153,9 @@ static ssize_t report_error_write(struct file *filp, struct kobject *kobj,
 	if (off || (count < sizeof(*report)))
 		return -EINVAL;
 
+	if (count < (report->length + sizeof(*report)))
+		return -EINVAL;
+
 	ret = sclp_pci_report(report, zdev->fh, zdev->fid);
 
 	return ret ? ret : count;

---
base-commit: 075b74841bd0065a3bda3440873c747938e69b68
change-id: 20260803-fix_pci_sclp_length_check-aa68495b1990

Best regards,
-- 
Niklas Schnelle

On Thu, Aug 06, 2026 at 11:43:39AM +0200, Niklas Schnelle wrote:
> While report_error_write() checks that the provided buffer is at least
> as large as the header struct, but not that it is large enough to
> contain the report with the length claimed by report->length. If
> user-space provides a short buffer, meaning a larger report->length than
> the actually written payload, up to around 4K of kernel data from past
> the kmalloc(len + 1) sized buffer allocated in kernfs_fop_write_iter()
> will leak into the SCLP report.
> 
> However, as the entity processing the SCLP is privileged and able to
> access at least the page including the report, this does not leak data
> that entity could not access but it is still an out of bounds read and
> a malformed error report that should be rejected.
> 
> Fixes: 368704a65be8 ("s390/pci: add report_error attribute")
> Cc: stable@vger.kernel.org
> Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
> ---
> Changes in v2:
> - Changed subsystem prefix to s390/pci
> - Added Fixes tag and Cc stable
> - Improved commit message
> - Link to v1: https://lore.kernel.org/r/20260805-fix_pci_sclp_length_check-v1-1-d125cb415bc3@linux.ibm.com
> ---
>  arch/s390/pci/pci_sysfs.c | 3 +++
>  1 file changed, 3 insertions(+)

Applied, thank you!

On Thu, Aug 06, 2026 at 11:43:39AM +0200, Niklas Schnelle wrote:
> While report_error_write() checks that the provided buffer is at least
> as large as the header struct, but not that it is large enough to
> contain the report with the length claimed by report->length. If
> user-space provides a short buffer, meaning a larger report->length than
> the actually written payload, up to around 4K of kernel data from past
> the kmalloc(len + 1) sized buffer allocated in kernfs_fop_write_iter()
> will leak into the SCLP report.
> 
> However, as the entity processing the SCLP is privileged and able to
> access at least the page including the report, this does not leak data
> that entity could not access but it is still an out of bounds read and
> a malformed error report that should be rejected.
> 
> Fixes: 368704a65be8 ("s390/pci: add report_error attribute")
> Cc: stable@vger.kernel.org
> Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
> ---
> Changes in v2:
> - Changed subsystem prefix to s390/pci
> - Added Fixes tag and Cc stable
> - Improved commit message
> - Link to v1: https://lore.kernel.org/r/20260805-fix_pci_sclp_length_check-v1-1-d125cb415bc3@linux.ibm.com
> ---
>  arch/s390/pci/pci_sysfs.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/s390/pci/pci_sysfs.c b/arch/s390/pci/pci_sysfs.c
> index d98d97df792a..bbb76113a4d0 100644
> --- a/arch/s390/pci/pci_sysfs.c
> +++ b/arch/s390/pci/pci_sysfs.c
> @@ -153,6 +153,9 @@ static ssize_t report_error_write(struct file *filp, struct kobject *kobj,
>  	if (off || (count < sizeof(*report)))
>  		return -EINVAL;
>  
> +	if (count < (report->length + sizeof(*report)))
> +		return -EINVAL;
> +
>  	ret = sclp_pci_report(report, zdev->fh, zdev->fid);
>  
>  	return ret ? ret : count;

Looks good to me.


Reviewed-by: Benjamin Block <bblock@linux.ibm.com>

-- 
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