Just like vfs_read(), uverbs_write() must check output buffer
(eg. response) with access_ok(VERIFY_WRITE,...) to ensure
it's in userspace memory before using the pointer in uverbs
functions.

If the buffer or a subset of the buffer is not valid,
returns -EFAULT.

Note: there's no need to check input buffer (eg. command)
since vfs_write() does the check access_ok(VERIFY_READ, ...)
as part of write() syscall.

Link: http://marc.info/[email protected]>
Signed-off-by: Yann Droneaud <[email protected]>
---
 drivers/infiniband/core/uverbs_main.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/infiniband/core/uverbs_main.c 
b/drivers/infiniband/core/uverbs_main.c
index 8652c13f6ea2..0be1dd86f768 100644
--- a/drivers/infiniband/core/uverbs_main.c
+++ b/drivers/infiniband/core/uverbs_main.c
@@ -677,6 +677,11 @@ static ssize_t ib_uverbs_write(struct file *filp, const 
char __user *buf,
                if (response) {
                        if (!hdr.out_words && !ex_hdr.provider_out_words)
                                return -EINVAL;
+
+                       if (!access_ok(VERIFY_WRITE,
+                                      response,
+                                      (hdr.out_words + 
ex_hdr.provider_out_words) * 8))
+                               return -EFAULT;
                } else {
                        if (hdr.out_words || ex_hdr.provider_out_words)
                                return -EINVAL;
-- 
1.8.4.2

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