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Subject[PATCH 4.4 32/53] pipe: avoid round_pipe_size() nr_pages overflow on 32-bit
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Joe Lawrence <joe.lawrence@redhat.com>

commit d3f14c485867cfb2e0c48aa88c41d0ef4bf5209c upstream.

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>
Signed-off-by: Dong Jinguang <dongjinguang@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/pipe.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)

--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1001,6 +1001,9 @@ static long pipe_set_size(struct pipe_in
{
struct pipe_buffer *bufs;

+ if (!nr_pages)
+ return -EINVAL;
+
/*
* We can shrink the pipe, if arg >= pipe->nrbufs. Since we don't
* expect a lot of shrink+grow operations, just free and allocate
@@ -1045,13 +1048,19 @@ static long pipe_set_size(struct pipe_in

/*
* 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;
}

@@ -1062,13 +1071,18 @@ static inline unsigned int round_pipe_si
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_dointvec_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;
}


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