pipe: simplify round_pipe_size()

round_pipe_size() calculates the number of pages the requested size
corresponds to, then rounds the page count up to the next power of 2.

However, it also rounds everything < PAGE_SIZE up to PAGE_SIZE.
Therefore, there's no need to actually translate the size into a page
count; we just need to round the size up to the next power of 2.

We do need to verify the size isn't greater than (1 << 31), since on
32-bit systems roundup_pow_of_two() would be undefined in that case.  But
that can just be combined with the UINT_MAX check which we need anyway
now.

Finally, update pipe_set_size() to not redundantly check the return value
of round_pipe_size() for the "invalid size" case twice.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Eric Biggers <[email protected]>
Acked-by: Kees Cook <[email protected]>
Acked-by: Joe Lawrence <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: "Luis R . Rodriguez" <[email protected]>
Cc: Michael Kerrisk <[email protected]>
Cc: Mikulas Patocka <[email protected]>
Cc: Willy Tarreau <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/fs/pipe.c b/fs/pipe.c
index 817393d362445a4bf065d4dd29e0acba06044cb6..8be52158c400cf765006433bd2389aa71a1f048a 100644 (file)
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1022,20 +1022,14 @@ const struct file_operations pipefifo_fops = {
  */
 unsigned int round_pipe_size(unsigned long size)
 {
-       unsigned long nr_pages;
-
-       if (size > UINT_MAX)
+       if (size > (1U << 31))
                return 0;
 
        /* Minimum pipe size, as required by POSIX */
        if (size < PAGE_SIZE)
-               size = PAGE_SIZE;
-
-       nr_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
-       if (nr_pages == 0)
-               return 0;
+               return PAGE_SIZE;
 
-       return roundup_pow_of_two(nr_pages) << PAGE_SHIFT;
+       return roundup_pow_of_two(size);
 }
 
 /*
@@ -1050,8 +1044,6 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
        long ret = 0;
 
        size = round_pipe_size(arg);
-       if (size == 0)
-               return -EINVAL;
        nr_pages = size >> PAGE_SHIFT;
 
        if (!nr_pages)