linux-kernel - [PATCH] fs/pipe: use kvcalloc to allocate a pipe

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Message-Id: <20220104171058.22580-1-avagin@gmail.com>
Date:   Tue,  4 Jan 2022 09:10:58 -0800
From:   Andrei Vagin <avagin@...il.com>
To:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>
Cc:     linux-fsdevel@...r.kernel.org, Andrei Vagin <avagin@...il.com>,
        Dmitry Safonov <0x7f454c46@...il.com>
Subject: [PATCH] fs/pipe: use kvcalloc to allocate a pipe_buffer array

Right now, kcalloc is used to allocate a pipe_buffer array.  The size of
the pipe_buffer struct is 40 bytes. kcalloc allows allocating reliably
chunks with sizes less or equal to PAGE_ALLOC_COSTLY_ORDER (3). It means
that the maximum pipe size is 3.2MB in this case.

In CRIU, we use pipes to dump processes memory. CRIU freezes a target
process, injects a parasite code into it and then this code splices
memory into pipes. If a maximum pipe size is small, we need to
do many iterations or create many pipes.

kvcalloc attempt to allocate physically contiguous memory, but upon
failure, fall back to non-contiguous (vmalloc) allocation and so it
isn't limited by PAGE_ALLOC_COSTLY_ORDER.

The maximum pipe size for non-root users is limited by
the /proc/sys/fs/pipe-max-size sysctl that is 1MB by default, so only
the root user will be able to trigger vmalloc allocations.

Cc: Dmitry Safonov <0x7f454c46@...il.com>
Signed-off-by: Andrei Vagin <avagin@...il.com>
---
 fs/pipe.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index 6d4342bad9f1..45565773ec33 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -802,7 +802,7 @@ struct pipe_inode_info *alloc_pipe_info(void)
 	if (too_many_pipe_buffers_hard(user_bufs) && pipe_is_unprivileged_user())
 		goto out_revert_acct;

-	pipe->bufs = kcalloc(pipe_bufs, sizeof(struct pipe_buffer),
+	pipe->bufs = kvcalloc(pipe_bufs, sizeof(struct pipe_buffer),
 			     GFP_KERNEL_ACCOUNT);

 	if (pipe->bufs) {
@@ -845,7 +845,7 @@ void free_pipe_info(struct pipe_inode_info *pipe)
 	}
 	if (pipe->tmp_page)
 		__free_page(pipe->tmp_page);
-	kfree(pipe->bufs);
+	kvfree(pipe->bufs);
 	kfree(pipe);
 }

@@ -1260,8 +1260,7 @@ int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)
 	if (nr_slots < n)
 		return -EBUSY;

-	bufs = kcalloc(nr_slots, sizeof(*bufs),
-		       GFP_KERNEL_ACCOUNT | __GFP_NOWARN);
+	bufs = kvcalloc(nr_slots, sizeof(*bufs), GFP_KERNEL_ACCOUNT);
 	if (unlikely(!bufs))
 		return -ENOMEM;

@@ -1288,7 +1287,7 @@ int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)
 	head = n;
 	tail = 0;

-	kfree(pipe->bufs);
+	kvfree(pipe->bufs);
 	pipe->bufs = bufs;
 	pipe->ring_size = nr_slots;
 	if (pipe->max_usage > nr_slots)
-- 
2.33.1