Limit the number of slots in pipe_resize_ring() to the maximum value
representable by pipe->{head,tail}. Values beyond the max limit can
lead to incorrect pipe occupancy related calculations where the pipe
will never appear full.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
---
Changelog:
RFC v1..v2:
o Use (pipe_index_t)-1u as the limit instead of BITS_PER_TYPE()
hackery. (Oleg)
o Added the "Suggested-by:" tag.
---
fs/pipe.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/fs/pipe.c b/fs/pipe.c
index 4d0799e4e719..88e81f84e3ea 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1271,6 +1271,10 @@ int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)
struct pipe_buffer *bufs;
unsigned int head, tail, mask, n;
+ /* nr_slots larger than limits of pipe->{head,tail} */
+ if (unlikely(nr_slots > (pipe_index_t)-1u))
+ return -EINVAL;
+
bufs = kcalloc(nr_slots, sizeof(*bufs),
GFP_KERNEL_ACCOUNT | __GFP_NOWARN);
if (unlikely(!bufs))
--
2.43.0On 03/07, K Prateek Nayak wrote:
>
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -1271,6 +1271,10 @@ int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)
> struct pipe_buffer *bufs;
> unsigned int head, tail, mask, n;
>
> + /* nr_slots larger than limits of pipe->{head,tail} */
> + if (unlikely(nr_slots > (pipe_index_t)-1u))
> + return -EINVAL;
The whole series look "obviously" good to me,
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
-------------------------------------------------------------------------------
But damn ;) lets look at round_pipe_size(),
unsigned int round_pipe_size(unsigned int size)
{
if (size > (1U << 31))
return 0;
/* Minimum pipe size, as required by POSIX */
if (size < PAGE_SIZE)
return PAGE_SIZE;
return roundup_pow_of_two(size);
}
it is a bit silly to allow the maximum size == 1U << 31 in pipe_set_size()
or (more importantly) in /proc/sys/fs/pipe-max-size, and then nack nr_slots
in pipe_resize_ring().
So perhaps this check should go into round_pipe_size() ? Although I can't
suggest a simple/clear check without unnecesary restrictions for the case
when pipe_index_t is u16.
pipe_resize_ring() has another caller, watch_queue_set_size(), but it has
its own hard limits...
Oleg.
Hello Oleg,
Thank you for the review.
On 3/7/2025 8:21 PM, Oleg Nesterov wrote:
> On 03/07, K Prateek Nayak wrote:
>>
>> --- a/fs/pipe.c
>> +++ b/fs/pipe.c
>> @@ -1271,6 +1271,10 @@ int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)
>> struct pipe_buffer *bufs;
>> unsigned int head, tail, mask, n;
>>
>> + /* nr_slots larger than limits of pipe->{head,tail} */
>> + if (unlikely(nr_slots > (pipe_index_t)-1u))
>> + return -EINVAL;
>
> The whole series look "obviously" good to me,
>
> Reviewed-by: Oleg Nesterov <oleg@redhat.com>
>
> -------------------------------------------------------------------------------
> But damn ;) lets look at round_pipe_size(),
>
> unsigned int round_pipe_size(unsigned int size)
> {
> if (size > (1U << 31))
> return 0;
>
> /* Minimum pipe size, as required by POSIX */
> if (size < PAGE_SIZE)
> return PAGE_SIZE;
>
> return roundup_pow_of_two(size);
> }
>
> it is a bit silly to allow the maximum size == 1U << 31 in pipe_set_size()
> or (more importantly) in /proc/sys/fs/pipe-max-size, and then nack nr_slots
> in pipe_resize_ring().
>
> So perhaps this check should go into round_pipe_size() ? Although I can't
> suggest a simple/clear check without unnecesary restrictions for the case
> when pipe_index_t is u16.
>
> pipe_resize_ring() has another caller, watch_queue_set_size(), but it has
> its own hard limits...
"nr_notes" for watch queues cannot cross 512 so we should be covered there.
As for round_pipe_size(), we can do:
diff --git a/fs/pipe.c b/fs/pipe.c
index ce1af7592780..f82098aaa510 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1253,6 +1253,8 @@ const struct file_operations pipefifo_fops = {
*/
unsigned int round_pipe_size(unsigned int size)
{
+ unsigned int max_slots;
+
if (size > (1U << 31))
return 0;
@@ -1260,7 +1262,14 @@ unsigned int round_pipe_size(unsigned int size)
if (size < PAGE_SIZE)
return PAGE_SIZE;
- return roundup_pow_of_two(size);
+ size = roundup_pow_of_two(size);
+ max_slots = size >> PAGE_SHIFT;
+
+ /* Max slots cannot be covered pipe->{head,tail} limits */
+ if (max_slots > (pipe_index_t)-1U)
+ return 0;
+
+ return size;
}
/*
--
Since pipe_resize_ring() can be called without actually looking at
"pipe_max_size" as is the case with watch queues, we can either keep the
check in pipe_resize_ring() as well out of paranoia or get rid of it
since the current users are within the bounds.
Thoughts?
>
> Oleg.
>
--
Thanks and Regards,
Prateek
On 03/07, K Prateek Nayak wrote:
>
> On 3/7/2025 8:21 PM, Oleg Nesterov wrote:
> >On 03/07, K Prateek Nayak wrote:
> >>
> >>--- a/fs/pipe.c
> >>+++ b/fs/pipe.c
> >>@@ -1271,6 +1271,10 @@ int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)
> >> struct pipe_buffer *bufs;
> >> unsigned int head, tail, mask, n;
> >>
> >>+ /* nr_slots larger than limits of pipe->{head,tail} */
> >>+ if (unlikely(nr_slots > (pipe_index_t)-1u))
> >>+ return -EINVAL;
> >
> >The whole series look "obviously" good to me,
> >
> >Reviewed-by: Oleg Nesterov <oleg@redhat.com>
So, in case it wasn't clear, you could safely ignore everything else below ;)
> >pipe_resize_ring() has another caller, watch_queue_set_size(), but it has
> >its own hard limits...
>
> "nr_notes" for watch queues cannot cross 512 so we should be covered there.
Yes, yes, this is what I meant,
> As for round_pipe_size(), we can do:
>
> diff --git a/fs/pipe.c b/fs/pipe.c
> index ce1af7592780..f82098aaa510 100644
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -1253,6 +1253,8 @@ const struct file_operations pipefifo_fops = {
> */
> unsigned int round_pipe_size(unsigned int size)
> {
> + unsigned int max_slots;
> +
> if (size > (1U << 31))
> return 0;
> @@ -1260,7 +1262,14 @@ unsigned int round_pipe_size(unsigned int size)
> if (size < PAGE_SIZE)
> return PAGE_SIZE;
> - return roundup_pow_of_two(size);
> + size = roundup_pow_of_two(size);
> + max_slots = size >> PAGE_SHIFT;
> +
> + /* Max slots cannot be covered pipe->{head,tail} limits */
> + if (max_slots > (pipe_index_t)-1U)
> + return 0;
Sure, this will work, but still it doesn't look clear/clean to me.
But no, no, I don't blame your suggestion.
To me, round_pipe_size() looks confusing with or without the changes we
discuss. Why does it use "1U << 31" as a maximum size? OK, this is because
that "1 << 31" is the maximum power-of-2 which can fit into u32.
But, even if this code assumes that pipe->head/tail are u32, why this
restriction? Most probably I missed something, but I don't understand.
> Since pipe_resize_ring() can be called without actually looking at
> "pipe_max_size"
Again, only if the caller is watch_queue_set_size(), but it has its own
hard limit.
So. I won't argue either way. Whatever looks better to you. My ack
still stands.
Sorry for (yet another) confusing and almost off-topic email from me.
Oleg.
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