[PATCH 03/15] splice: move permission hook out of splice_direct_to_actor()

Amir Goldstein
2023-11-14T15:33:07Z

vfs_splice_read() has a permission hook inside rw_verify_area() and
it is called from do_splice_direct() -> splice_direct_to_actor().

The callers of do_splice_direct() (e.g. vfs_copy_file_range()) already
call rw_verify_area() for the entire range, but the other caller of
splice_direct_to_actor() (nfsd) does not.

Add the rw_verify_area() checks in nfsd_splice_read() and use a
variant of vfs_splice_read() without rw_verify_area() check in
splice_direct_to_actor() to avoid the redundant rw_verify_area() checks.

This is needed for fanotify "pre content" events.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
fs/nfsd/vfs.c | 5 ++++-
fs/splice.c | 58 +++++++++++++++++++++++++++++++--------------------
2 files changed, 39 insertions(+), 24 deletions(-)

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index fbbea7498f02..5d704461e3b4 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1046,7 +1046,10 @@ __be32 nfsd_splice_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
ssize_t host_err;

trace_nfsd_read_splice(rqstp, fhp, offset, *count);
- host_err = splice_direct_to_actor(file, &sd, nfsd_direct_splice_actor);
+ host_err = rw_verify_area(READ, file, &offset, *count);
+ if (!host_err)
+ host_err = splice_direct_to_actor(file, &sd,
+ nfsd_direct_splice_actor);
return nfsd_finish_read(rqstp, fhp, file, offset, count, eof, host_err);
}

diff --git a/fs/splice.c b/fs/splice.c
index 6e917db6f49a..6fc2c27e9520 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -944,27 +944,15 @@ static void do_splice_eof(struct splice_desc *sd)
sd->splice_eof(sd);
}

-/**
- * vfs_splice_read - Read data from a file and splice it into a pipe
- * @in: File to splice from
- * @ppos: Input file offset
- * @pipe: Pipe to splice to
- * @len: Number of bytes to splice
- * @flags: Splice modifier flags (SPLICE_F_*)
- *
- * Splice the requested amount of data from the input file to the pipe. This
- * is synchronous as the caller must hold the pipe lock across the entire
- * operation.
- *
- * If successful, it returns the amount of data spliced, 0 if it hit the EOF or
- * a hole and a negative error code otherwise.
+/*
+ * Callers already called rw_verify_area() on the entire range.
+ * No need to call it for sub ranges.
*/
-long vfs_splice_read(struct file *in, loff_t *ppos,
- struct pipe_inode_info *pipe, size_t len,
- unsigned int flags)
+static long do_splice_read(struct file *in, loff_t *ppos,
+ struct pipe_inode_info *pipe, size_t len,
+ unsigned int flags)
{
unsigned int p_space;
- int ret;

if (unlikely(!(in->f_mode & FMODE_READ)))
return -EBADF;
@@ -975,10 +963,6 @@ long vfs_splice_read(struct file *in, loff_t *ppos,
p_space = pipe->max_usage - pipe_occupancy(pipe->head, pipe->tail);
len = min_t(size_t, len, p_space << PAGE_SHIFT);

- ret = rw_verify_area(READ, in, ppos, len);
- if (unlikely(ret < 0))
- return ret;
-
if (unlikely(len > MAX_RW_COUNT))
len = MAX_RW_COUNT;

@@ -992,6 +976,34 @@ long vfs_splice_read(struct file *in, loff_t *ppos,
return copy_splice_read(in, ppos, pipe, len, flags);
return in->f_op->splice_read(in, ppos, pipe, len, flags);
}
+
+/**
+ * vfs_splice_read - Read data from a file and splice it into a pipe
+ * @in: File to splice from
+ * @ppos: Input file offset
+ * @pipe: Pipe to splice to
+ * @len: Number of bytes to splice
+ * @flags: Splice modifier flags (SPLICE_F_*)
+ *
+ * Splice the requested amount of data from the input file to the pipe. This
+ * is synchronous as the caller must hold the pipe lock across the entire
+ * operation.
+ *
+ * If successful, it returns the amount of data spliced, 0 if it hit the EOF or
+ * a hole and a negative error code otherwise.
+ */
+long vfs_splice_read(struct file *in, loff_t *ppos,
+ struct pipe_inode_info *pipe, size_t len,
+ unsigned int flags)
+{
+ int ret;
+
+ ret = rw_verify_area(READ, in, ppos, len);
+ if (unlikely(ret < 0))
+ return ret;
+
+ return do_splice_read(in, ppos, pipe, len, flags);
+}
EXPORT_SYMBOL_GPL(vfs_splice_read);

/**
@@ -1066,7 +1078,7 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
size_t read_len;
loff_t pos = sd->pos, prev_pos = pos;

- ret = vfs_splice_read(in, &pos, pipe, len, flags);
+ ret = do_splice_read(in, &pos, pipe, len, flags);
if (unlikely(ret <= 0))
goto read_failure;

--
2.34.1