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pipe: avoid round_pipe_size() nr_pages overflow on 32-bit

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round_pipe_size() contains a right-bit-shift expression which may
overflow, which would cause undefined results in a subsequent
roundup_pow_of_two() call.

  static inline unsigned int round_pipe_size(unsigned int size)
  {
          unsigned long nr_pages;

          nr_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
          return roundup_pow_of_two(nr_pages) << PAGE_SHIFT;
  }

PAGE_SIZE is defined as (1UL << PAGE_SHIFT), so:
  - 4 bytes wide on 32-bit (0 to 0xffffffff)
  - 8 bytes wide on 64-bit (0 to 0xffffffffffffffff)

That means that 32-bit round_pipe_size(), nr_pages may overflow to 0:

  size=0x00000000    nr_pages=0x0
  size=0x00000001    nr_pages=0x1
  size=0xfffff000    nr_pages=0xfffff
  size=0xfffff001    nr_pages=0x0         << !
  size=0xffffffff    nr_pages=0x0         << !

This is bad because roundup_pow_of_two(n) is undefined when n == 0!

64-bit is not a problem as the unsigned int size is 4 bytes wide
(similar to 32-bit) and the larger, 8 byte wide unsigned long, is
sufficient to handle the largest value of the bit shift expression:

  size=0xffffffff    nr_pages=100000

Modify round_pipe_size() to return 0 if n == 0 and updates its callers to
handle accordingly.

Link: http://lkml.kernel.org/r/1507658689-11669-3-git-send-email-joe.lawrence@redhat.com
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Reported-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Joe Lawrence 2017-11-17 15:29:21 -08:00 committed by Linus Torvalds
parent 98159d977f
commit d3f14c4858
1 changed files with 15 additions and 2 deletions
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17
fs/pipe.c
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@ -1018,13 +1018,19 @@ const struct file_operations pipefifo_fops = {
/*
* Currently we rely on the pipe array holding a power-of-2 number
* of pages.
* of pages. Returns 0 on error.
*/
static inline unsigned int round_pipe_size(unsigned int size)
{
unsigned long nr_pages;
if (size < pipe_min_size)
size = pipe_min_size;
nr_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
if (nr_pages == 0)
return 0;
return roundup_pow_of_two(nr_pages) << PAGE_SHIFT;
}
@ -1040,6 +1046,8 @@ 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)
@ -1123,13 +1131,18 @@ out_revert_acct:
int pipe_proc_fn(struct ctl_table *table, int write, void __user *buf,
size_t *lenp, loff_t *ppos)
{
unsigned int rounded_pipe_max_size;
int ret;
ret = proc_douintvec_minmax(table, write, buf, lenp, ppos);
if (ret < 0 || !write)
return ret;
pipe_max_size = round_pipe_size(pipe_max_size);
rounded_pipe_max_size = round_pipe_size(pipe_max_size);
if (rounded_pipe_max_size == 0)
return -EINVAL;
pipe_max_size = rounded_pipe_max_size;
return ret;
}