[PATCH v2] s390/pci: Fix leak of uninitialized kernel data in SCLP report

[Niklas Schnelle <schnelle@linux.ibm.com>]

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