fs/select.c: use struct_size() in kmalloc()

One of the more common cases of allocation size calculations is finding
the size of a structure that has a zero-sized array at the end, along
with memory for some number of elements for that array.  For example:

  struct foo {
       int stuff;
       struct boo entry[];
  };

  size = sizeof(struct foo) + count * sizeof(struct boo);
  instance = kmalloc(size, GFP_KERNEL);

Instead of leaving these open-coded and prone to type mistakes, we can now
use the new struct_size() helper:

  instance = kmalloc(struct_size(instance, entry, count), GFP_KERNEL);

Also, notice that variable size is unnecessary, hence it is removed.

This code was detected with the help of Coccinelle.

Link: http://lkml.kernel.org/r/20190604164226.GA13823@embeddedor
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/fs/select.c b/fs/select.c
index 51ceec292f2f..53a0c149f528 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -961,7 +961,7 @@ static int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds,
                 struct timespec64 *end_time)
 {
         struct poll_wqueues table;
-        int err = -EFAULT, fdcount, len, size;
+        int err = -EFAULT, fdcount, len;
         /* Allocate small arguments on the stack to save memory and be
            faster - use long to make sure the buffer is aligned properly
            on 64 bit archs to avoid unaligned access */
@@ -989,8 +989,8 @@ static int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds,
                         break;
 
                 len = min(todo, POLLFD_PER_PAGE);
-                size = sizeof(struct poll_list) + sizeof(struct pollfd) * len;
-                walk = walk->next = kmalloc(size, GFP_KERNEL);
+                walk = walk->next = kmalloc(struct_size(walk, entries, len),
+                                            GFP_KERNEL);
                 if (!walk) {
                         err = -ENOMEM;
                         goto out_fds;