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() calculations where the pipe will
never appear full.

Since nr_slots is always a power of 2 and the maximum size of
pipe_index_t is 32 bits, BIT() is sufficient to represent the maximum
value possible for nr_slots.

Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
---
 fs/pipe.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/pipe.c b/fs/pipe.c
index e8e6698f3698..3ca3103e1de7 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1272,6 +1272,10 @@ 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 > BIT(BITS_PER_TYPE(pipe_index_t) - 1)))
+		return -EINVAL;
+
 	bufs = kcalloc(nr_slots, sizeof(*bufs),
 		       GFP_KERNEL_ACCOUNT | __GFP_NOWARN);
 	if (unlikely(!bufs))

base-commit: 848e076317446f9c663771ddec142d7c2eb4cb43
-- 
2.43.0

On 03/06, K Prateek Nayak wrote:
>
> @@ -1272,6 +1272,10 @@ 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 > BIT(BITS_PER_TYPE(pipe_index_t) - 1)))

Hmm, perhaps

	if (nr_slots > (pipe_index_t)-1u)

is more clear?

Oleg.

Hello Oleg,

On 3/6/2025 5:58 PM, Oleg Nesterov wrote:
> On 03/06, K Prateek Nayak wrote:
>>
>> @@ -1272,6 +1272,10 @@ 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 > BIT(BITS_PER_TYPE(pipe_index_t) - 1)))
> 
> Hmm, perhaps
> 
> 	if (nr_slots > (pipe_index_t)-1u)
> 
> is more clear?

Indeed it is. I didn't even know we could do that! Thank you for
pointing it out.

> 
> Oleg.
> 

-- 
Thanks and Regards,
Prateek