[PATCH 5.10 03/15] vfs: fix copy_file_range() averts filesystem freeze protection

Greg Kroah-Hartman
2022-12-15T18:11:47Z

From: Amir Goldstein <amir73il@gmail.com>

commit 10bc8e4af65946b727728d7479c028742321b60a upstream.

[backport comments for pre v5.15:
- ksmbd mentions are irrelevant - ksmbd hunks were dropped
- sb_write_started() is missing - assert was dropped
]

Commit 868f9f2f8e00 ("vfs: fix copy_file_range() regression in cross-fs
copies") removed fallback to generic_copy_file_range() for cross-fs
cases inside vfs_copy_file_range().

To preserve behavior of nfsd and ksmbd server-side-copy, the fallback to
generic_copy_file_range() was added in nfsd and ksmbd code, but that
call is missing sb_start_write(), fsnotify hooks and more.

Ideally, nfsd and ksmbd would pass a flag to vfs_copy_file_range() that
will take care of the fallback, but that code would be subtle and we got
vfs_copy_file_range() logic wrong too many times already.

Instead, add a flag to explicitly request vfs_copy_file_range() to
perform only generic_copy_file_range() and let nfsd and ksmbd use this
flag only in the fallback path.

This choise keeps the logic changes to minimum in the non-nfsd/ksmbd code
paths to reduce the risk of further regressions.

Fixes: 868f9f2f8e00 ("vfs: fix copy_file_range() regression in cross-fs copies")
Tested-by: Namjae Jeon <linkinjeon@kernel.org>
Tested-by: Luis Henriques <lhenriques@suse.de>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/nfsd/vfs.c | 4 ++--
fs/read_write.c | 17 +++++++++++++----
include/linux/fs.h | 8 ++++++++
3 files changed, 23 insertions(+), 6 deletions(-)

--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -584,8 +584,8 @@ ssize_t nfsd_copy_file_range(struct file
ret = vfs_copy_file_range(src, src_pos, dst, dst_pos, count, 0);

if (ret == -EOPNOTSUPP || ret == -EXDEV)
- ret = generic_copy_file_range(src, src_pos, dst, dst_pos,
- count, 0);
+ ret = vfs_copy_file_range(src, src_pos, dst, dst_pos, count,
+ COPY_FILE_SPLICE);
return ret;
}

--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1419,7 +1419,9 @@ static int generic_copy_file_checks(stru
* and several different sets of file_operations, but they all end up
* using the same ->copy_file_range() function pointer.
*/
- if (file_out->f_op->copy_file_range) {
+ if (flags & COPY_FILE_SPLICE) {
+ /* cross sb splice is allowed */
+ } else if (file_out->f_op->copy_file_range) {
if (file_in->f_op->copy_file_range !=
file_out->f_op->copy_file_range)
return -EXDEV;
@@ -1469,8 +1471,9 @@ ssize_t vfs_copy_file_range(struct file
size_t len, unsigned int flags)
{
ssize_t ret;
+ bool splice = flags & COPY_FILE_SPLICE;

- if (flags != 0)
+ if (flags & ~COPY_FILE_SPLICE)
return -EINVAL;

ret = generic_copy_file_checks(file_in, pos_in, file_out, pos_out, &len,
@@ -1496,14 +1499,14 @@ ssize_t vfs_copy_file_range(struct file
* same sb using clone, but for filesystems where both clone and copy
* are supported (e.g. nfs,cifs), we only call the copy method.
*/
- if (file_out->f_op->copy_file_range) {
+ if (!splice && file_out->f_op->copy_file_range) {
ret = file_out->f_op->copy_file_range(file_in, pos_in,
file_out, pos_out,
len, flags);
goto done;
}

- if (file_in->f_op->remap_file_range &&
+ if (!splice && file_in->f_op->remap_file_range &&
file_inode(file_in)->i_sb == file_inode(file_out)->i_sb) {
ret = file_in->f_op->remap_file_range(file_in, pos_in,
file_out, pos_out,
@@ -1523,6 +1526,8 @@ ssize_t vfs_copy_file_range(struct file
* consistent story about which filesystems support copy_file_range()
* and which filesystems do not, that will allow userspace tools to
* make consistent desicions w.r.t using copy_file_range().
+ *
+ * We also get here if caller (e.g. nfsd) requested COPY_FILE_SPLICE.
*/
ret = generic_copy_file_range(file_in, pos_in, file_out, pos_out, len,
flags);
@@ -1577,6 +1582,10 @@ SYSCALL_DEFINE6(copy_file_range, int, fd
pos_out = f_out.file->f_pos;
}

+ ret = -EINVAL;
+ if (flags != 0)
+ goto out;
+
ret = vfs_copy_file_range(f_in.file, pos_in, f_out.file, pos_out, len,
flags);
if (ret > 0) {
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1817,6 +1817,14 @@ struct dir_context {
*/
#define REMAP_FILE_ADVISORY (REMAP_FILE_CAN_SHORTEN)

+/*
+ * These flags control the behavior of vfs_copy_file_range().
+ * They are not available to the user via syscall.
+ *
+ * COPY_FILE_SPLICE: call splice direct instead of fs clone/copy ops
+ */
+#define COPY_FILE_SPLICE (1 << 0)
+
struct iov_iter;

struct file_operations {