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fs: prevent page refcount overflow in pipe_buf_get

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>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Matthew Wilcox authored and torvalds committed Apr 5, 2019
1 parent 8fde12c commit 15fab63e1e57be9fdb5eec1bbc5916e9825e9acb
Showing with 29 additions and 15 deletions.
  1. +6 −6 fs/fuse/dev.c
  2. +2 −2 fs/pipe.c
  3. +10 −2 fs/splice.c
  4. +6 −4 include/linux/pipe_fs_i.h
  5. +5 −1 kernel/trace/trace.c
@@ -2034,10 +2034,8 @@ static ssize_t fuse_dev_splice_write(struct pipe_inode_info *pipe,
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) {
@@ -2055,7 +2053,9 @@ static ssize_t fuse_dev_splice_write(struct pipe_inode_info *pipe,
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;
@@ -2078,11 +2078,11 @@ static ssize_t fuse_dev_splice_write(struct pipe_inode_info *pipe,
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:
kvfree(bufs);
return ret;
}
@@ -189,9 +189,9 @@ 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);

@@ -1588,7 +1588,11 @@ static int splice_pipe_to_pipe(struct pipe_inode_info *ipipe,
* 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;

/*
@@ -1660,7 +1664,11 @@ static int link_pipe(struct pipe_inode_info *ipipe,
* 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;
@@ -108,18 +108,20 @@ 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);
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 *);
@@ -6835,12 +6835,16 @@ static void buffer_pipe_buf_release(struct pipe_inode_info *pipe,
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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