ibmasm: don't write out of bounds in read handler

This read handler had a lot of custom logic and wrote outside the bounds of
the provided buffer. This could lead to kernel and userspace memory
corruption. Just use simple_read_from_buffer() with a stack buffer.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 3 insertions, 24 deletions

diff --git a/drivers/misc/ibmasm/ibmasmfs.c b/drivers/misc/ibmasm/ibmasmfs.c
index e05c3245930a..fa840666bdd1 100644
--- a/drivers/misc/ibmasm/ibmasmfs.c
+++ b/drivers/misc/ibmasm/ibmasmfs.c
@@ -507,35 +507,14 @@ static int remote_settings_file_close(struct inode *inode, struct file *file)
 static ssize_t remote_settings_file_read(struct file *file, char __user *buf, size_t count, loff_t *offset)
 {
         void __iomem *address = (void __iomem *)file->private_data;
-        unsigned char *page;
-        int retval;
         int len = 0;
         unsigned int value;
-
-        if (*offset < 0)
-                return -EINVAL;
-        if (count == 0 || count > 1024)
-                return 0;
-        if (*offset != 0)
-                return 0;
-
-        page = (unsigned char *)__get_free_page(GFP_KERNEL);
-        if (!page)
-                return -ENOMEM;
+        char lbuf[20];
 
         value = readl(address);
-        len = sprintf(page, "%d\n", value);
-
-        if (copy_to_user(buf, page, len)) {
-                retval = -EFAULT;
-                goto exit;
-        }
-        *offset += len;
-        retval = len;
+        len = snprintf(lbuf, sizeof(lbuf), "%d\n", value);
 
-exit:
-        free_page((unsigned long)page);
-        return retval;
+        return simple_read_from_buffer(buf, count, offset, lbuf, len);
 }
 
 static ssize_t remote_settings_file_write(struct file *file, const char __user *ubuff, size_t count, loff_t *offset)