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Subject[PATCH AUTOSEL 4.19 53/53] fs: prevent page refcount overflow in pipe_buf_get
Date
From: Matthew Wilcox <willy@infradead.org>

[ Upstream commit 15fab63e1e57be9fdb5eec1bbc5916e9825e9acb ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.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(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index baaed4d05b22..249de20f752a 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1989,10 +1989,8 @@ 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) {
@@ -2010,7 +2008,9 @@ 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;
@@ -2033,11 +2033,11 @@ 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;
}
diff --git a/fs/pipe.c b/fs/pipe.c
index c51750ed4011..2a297bce381f 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -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);

diff --git a/fs/splice.c b/fs/splice.c
index 29e92b506394..3ca117e79ee4 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1584,7 +1584,11 @@ 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;

/*
@@ -1658,7 +1662,11 @@ 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;
diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
index 3ecd7ea212ae..bbee2caf5837 100644
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -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 *);
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c65cea71d1ee..b01260f7b445 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6816,12 +6816,16 @@ 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. */
--
2.19.1
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