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Subject[PATCH 4.9 54/83] fs: prevent page refcount overflow in pipe_buf_get
Date
From: Matthew Wilcox <willy@infradead.org>

commit 15fab63e1e57be9fdb5eec1bbc5916e9825e9acb upstream.

Change pipe_buf_get() to return a bool indicating whether it succeeded
in raising the refcount of the page (if the thing in the pipe is a page).
This removes another mechanism for overflowing the page refcount. All
callers converted to handle a failure.

Reported-by: Jann Horn <jannh@google.com>
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 4.9: adjust context]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/fuse/dev.c | 12 ++++++------
fs/pipe.c | 4 ++--
fs/splice.c | 12 ++++++++++--
include/linux/pipe_fs_i.h | 10 ++++++----
kernel/trace/trace.c | 6 +++++-
5 files changed, 29 insertions(+), 15 deletions(-)

--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1975,10 +1975,8 @@ static ssize_t fuse_dev_splice_write(str
rem += pipe->bufs[(pipe->curbuf + idx) & (pipe->buffers - 1)].len;

ret = -EINVAL;
- if (rem < len) {
- pipe_unlock(pipe);
- goto out;
- }
+ if (rem < len)
+ goto out_free;

rem = len;
while (rem) {
@@ -1996,7 +1994,9 @@ static ssize_t fuse_dev_splice_write(str
pipe->curbuf = (pipe->curbuf + 1) & (pipe->buffers - 1);
pipe->nrbufs--;
} else {
- pipe_buf_get(pipe, ibuf);
+ if (!pipe_buf_get(pipe, ibuf))
+ goto out_free;
+
*obuf = *ibuf;
obuf->flags &= ~PIPE_BUF_FLAG_GIFT;
obuf->len = rem;
@@ -2019,11 +2019,11 @@ static ssize_t fuse_dev_splice_write(str
ret = fuse_dev_do_write(fud, &cs, len);

pipe_lock(pipe);
+out_free:
for (idx = 0; idx < nbuf; idx++)
pipe_buf_release(pipe, &bufs[idx]);
pipe_unlock(pipe);

-out:
kfree(bufs);
return ret;
}
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -193,9 +193,9 @@ EXPORT_SYMBOL(generic_pipe_buf_steal);
* in the tee() system call, when we duplicate the buffers in one
* pipe into another.
*/
-void generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
+bool generic_pipe_buf_get(struct pipe_inode_info *pipe, struct pipe_buffer *buf)
{
- get_page(buf->page);
+ return try_get_page(buf->page);
}
EXPORT_SYMBOL(generic_pipe_buf_get);

--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1585,7 +1585,11 @@ retry:
* Get a reference to this pipe buffer,
* so we can copy the contents over.
*/
- pipe_buf_get(ipipe, ibuf);
+ if (!pipe_buf_get(ipipe, ibuf)) {
+ if (ret == 0)
+ ret = -EFAULT;
+ break;
+ }
*obuf = *ibuf;

/*
@@ -1659,7 +1663,11 @@ static int link_pipe(struct pipe_inode_i
* Get a reference to this pipe buffer,
* so we can copy the contents over.
*/
- pipe_buf_get(ipipe, ibuf);
+ if (!pipe_buf_get(ipipe, ibuf)) {
+ if (ret == 0)
+ ret = -EFAULT;
+ break;
+ }

obuf = opipe->bufs + nbuf;
*obuf = *ibuf;
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -107,18 +107,20 @@ struct pipe_buf_operations {
/*
* Get a reference to the pipe buffer.
*/
- void (*get)(struct pipe_inode_info *, struct pipe_buffer *);
+ bool (*get)(struct pipe_inode_info *, struct pipe_buffer *);
};

/**
* pipe_buf_get - get a reference to a pipe_buffer
* @pipe: the pipe that the buffer belongs to
* @buf: the buffer to get a reference to
+ *
+ * Return: %true if the reference was successfully obtained.
*/
-static inline void pipe_buf_get(struct pipe_inode_info *pipe,
+static inline __must_check bool pipe_buf_get(struct pipe_inode_info *pipe,
struct pipe_buffer *buf)
{
- buf->ops->get(pipe, buf);
+ return buf->ops->get(pipe, buf);
}

/**
@@ -178,7 +180,7 @@ struct pipe_inode_info *alloc_pipe_info(
void free_pipe_info(struct pipe_inode_info *);

/* Generic pipe buffer ops functions */
-void generic_pipe_buf_get(struct pipe_inode_info *, struct pipe_buffer *);
+bool generic_pipe_buf_get(struct pipe_inode_info *, struct pipe_buffer *);
int generic_pipe_buf_confirm(struct pipe_inode_info *, struct pipe_buffer *);
int generic_pipe_buf_steal(struct pipe_inode_info *, struct pipe_buffer *);
void generic_pipe_buf_release(struct pipe_inode_info *, struct pipe_buffer *);
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6145,12 +6145,16 @@ static void buffer_pipe_buf_release(stru
buf->private = 0;
}

-static void buffer_pipe_buf_get(struct pipe_inode_info *pipe,
+static bool buffer_pipe_buf_get(struct pipe_inode_info *pipe,
struct pipe_buffer *buf)
{
struct buffer_ref *ref = (struct buffer_ref *)buf->private;

+ if (ref->ref > INT_MAX/2)
+ return false;
+
ref->ref++;
+ return true;
}

/* Pipe buffer operations for a buffer. */

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