scsi: lpfc: Prevent lpfc_debugfs_lockstat_write() buffer overflow

A static code analysis tool flagged the possibility of buffer overflow when
using copy_from_user() for a debugfs entry.

Currently, it is possible that copy_from_user() copies more bytes than what
would fit in the mybuf char array.  Add a min() restriction check between
sizeof(mybuf) - 1 and nbytes passed from the userspace buffer to protect
against buffer overflow.

Link: https://lore.kernel.org/r/20230301231626.9621-2-justintee8345@gmail.comSigned-off-by: Justin Tee <justin.tee@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/lpfc/lpfc_debugfs.c

@@ -2157,10 +2157,13 @@ lpfc_debugfs_lockstat_write(struct file *file, const char __user *buf,
 	char mybuf[64];
 	char *pbuf;
 	int i;
+	size_t bsize;
 
 	memset(mybuf, 0, sizeof(mybuf));
 
-	if (copy_from_user(mybuf, buf, nbytes))
+	bsize = min(nbytes, (sizeof(mybuf) - 1));
+
+	if (copy_from_user(mybuf, buf, bsize))
 		return -EFAULT;
 	pbuf = &mybuf[0];
 
@@ -2181,7 +2184,7 @@ lpfc_debugfs_lockstat_write(struct file *file, const char __user *buf,
 			qp->lock_conflict.wq_access = 0;
 		}
 	}
-	return nbytes;
+	return bsize;
 }
 #endif