Commit d3f14c48 authored by Joe Lawrence's avatar Joe Lawrence Committed by Linus Torvalds

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

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/[email protected]Signed-off-by: Joe Lawrence's avatarJoe Lawrence <[email protected]>
Reported-by: default avatarMikulas Patocka <[email protected]>
Reviewed-by: default avatarMikulas Patocka <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Michael Kerrisk <[email protected]>
Cc: Randy Dunlap <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Signed-off-by: default avatarAndrew Morton <[email protected]-foundation.org>
Signed-off-by: default avatarLinus Torvalds <[email protected]>
parent 98159d97
...@@ -1018,13 +1018,19 @@ const struct file_operations pipefifo_fops = { ...@@ -1018,13 +1018,19 @@ const struct file_operations pipefifo_fops = {
/* /*
* Currently we rely on the pipe array holding a power-of-2 number * 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) static inline unsigned int round_pipe_size(unsigned int size)
{ {
unsigned long nr_pages; unsigned long nr_pages;
if (size < pipe_min_size)
size = pipe_min_size;
nr_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT; nr_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
if (nr_pages == 0)
return 0;
return roundup_pow_of_two(nr_pages) << PAGE_SHIFT; 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) ...@@ -1040,6 +1046,8 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
long ret = 0; long ret = 0;
size = round_pipe_size(arg); size = round_pipe_size(arg);
if (size == 0)
return -EINVAL;
nr_pages = size >> PAGE_SHIFT; nr_pages = size >> PAGE_SHIFT;
if (!nr_pages) if (!nr_pages)
...@@ -1123,13 +1131,18 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg) ...@@ -1123,13 +1131,18 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
int pipe_proc_fn(struct ctl_table *table, int write, void __user *buf, int pipe_proc_fn(struct ctl_table *table, int write, void __user *buf,
size_t *lenp, loff_t *ppos) size_t *lenp, loff_t *ppos)
{ {
unsigned int rounded_pipe_max_size;
int ret; int ret;
ret = proc_douintvec_minmax(table, write, buf, lenp, ppos); ret = proc_douintvec_minmax(table, write, buf, lenp, ppos);
if (ret < 0 || !write) if (ret < 0 || !write)
return ret; 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; return ret;
} }
......
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