[PATCH v1 0/2] io-uring: Make statx api stable

[PATCH v1 0/2] io-uring: Make statx api stable

[Stefan Roesch]

One of the key architectual tenets of io-uring is to keep the
parameters for io-uring stable. After the call has been submitted,
its value can be changed.  Unfortunaltely this is not the case for
the current statx implementation.

Patches:
 Patch 1: fs: replace const char* parameter in vfs_statx and do_statx with
          struct filename
   Create filename object outside of do_statx and vfs_statx, so io-uring
   can create the filename object during the prepare phase

 Patch 2: io-uring: Copy path name during prepare stage for statx
   Create and store filename object during prepare phase


There is also a patch for the liburing libray to add a new test case. This
patch makes sure that the api is stable.
  "liburing: add test for stable statx api"

The patch has been tested with the liburing test suite and fstests.


Stefan Roesch (2):
  fs: replace const char* parameter in vfs_statx and do_statx with
    struct filename
  io-uring: Copy path name during prepare stage for statx

 fs/internal.h |  4 +++-
 fs/io_uring.c | 22 ++++++++++++++++++++--
 fs/stat.c     | 49 ++++++++++++++++++++++++++++++++++++-------------
 3 files changed, 59 insertions(+), 16 deletions(-)


base-commit: e6251ab4551f51fa4cee03523e08051898c3ce82
-- 
2.30.2

[PATCH v1 1/2] fs: replace const char* parameter in vfs_statx and do_statx with struct filename

[Stefan Roesch]

This replaces the const char* __user filename parameter in the two
functions do_statx and vfs_statx with a struct filename *. In addition
to be able to correctly construct a filename object a new helper
function getname_statx_lookup_flags is introduced. The function makes
sure that do_statx and vfs_statx is invoked with the correct lookup flags.

Signed-off-by: Stefan Roesch <shr@fb.com>
---
 fs/internal.h |  4 +++-
 fs/stat.c     | 49 ++++++++++++++++++++++++++++++++++++-------------
 2 files changed, 39 insertions(+), 14 deletions(-)

diff --git a/fs/internal.h b/fs/internal.h
index 8590c973c2f4..56c0477f4215 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -184,7 +184,9 @@ int sb_init_dio_done_wq(struct super_block *sb);
 /*
  * fs/stat.c:
  */
-int do_statx(int dfd, const char __user *filename, unsigned flags,
+
+int getname_statx_lookup_flags(int flags);
+int do_statx(int dfd, struct filename *filename, unsigned int flags,
 	     unsigned int mask, struct statx __user *buffer);
 
 /*
diff --git a/fs/stat.c b/fs/stat.c
index 28d2020ba1f4..6a11cfe6a849 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -184,6 +184,20 @@ int vfs_fstat(int fd, struct kstat *stat)
 	return error;
 }
 
+int getname_statx_lookup_flags(int flags)
+{
+	int lookup_flags = 0;
+
+	if (!(flags & AT_SYMLINK_NOFOLLOW))
+		lookup_flags |= LOOKUP_FOLLOW;
+	if (!(flags & AT_NO_AUTOMOUNT))
+		lookup_flags |= LOOKUP_AUTOMOUNT;
+	if (flags & AT_EMPTY_PATH)
+		lookup_flags |= LOOKUP_EMPTY;
+
+	return lookup_flags;
+}
+
 /**
  * vfs_statx - Get basic and extra attributes by filename
  * @dfd: A file descriptor representing the base dir for a relative filename
@@ -199,7 +213,7 @@ int vfs_fstat(int fd, struct kstat *stat)
  *
  * 0 will be returned on success, and a -ve error code if unsuccessful.
  */
-static int vfs_statx(int dfd, const char __user *filename, int flags,
+static int vfs_statx(int dfd, struct filename *filename, int flags,
 	      struct kstat *stat, u32 request_mask)
 {
 	struct path path;
@@ -210,15 +224,8 @@ static int vfs_statx(int dfd, const char __user *filename, int flags,
 		      AT_STATX_SYNC_TYPE))
 		return -EINVAL;
 
-	if (!(flags & AT_SYMLINK_NOFOLLOW))
-		lookup_flags |= LOOKUP_FOLLOW;
-	if (!(flags & AT_NO_AUTOMOUNT))
-		lookup_flags |= LOOKUP_AUTOMOUNT;
-	if (flags & AT_EMPTY_PATH)
-		lookup_flags |= LOOKUP_EMPTY;
-
 retry:
-	error = user_path_at(dfd, filename, lookup_flags, &path);
+	error = filename_lookup(dfd, filename, flags, &path, NULL);
 	if (error)
 		goto out;
 
@@ -240,8 +247,16 @@ static int vfs_statx(int dfd, const char __user *filename, int flags,
 int vfs_fstatat(int dfd, const char __user *filename,
 			      struct kstat *stat, int flags)
 {
-	return vfs_statx(dfd, filename, flags | AT_NO_AUTOMOUNT,
-			 stat, STATX_BASIC_STATS);
+	int ret;
+	int statx_flags = flags | AT_NO_AUTOMOUNT;
+	struct filename *name;
+
+	name = getname_flags(filename, getname_statx_lookup_flags(statx_flags), NULL);
+	ret = vfs_statx(dfd, name, statx_flags, stat, STATX_BASIC_STATS);
+	if (name)
+		putname(name);
+
+	return ret;
 }
 
 #ifdef __ARCH_WANT_OLD_STAT
@@ -602,7 +617,7 @@ cp_statx(const struct kstat *stat, struct statx __user *buffer)
 	return copy_to_user(buffer, &tmp, sizeof(tmp)) ? -EFAULT : 0;
 }
 
-int do_statx(int dfd, const char __user *filename, unsigned flags,
+int do_statx(int dfd, struct filename *filename, unsigned int flags,
 	     unsigned int mask, struct statx __user *buffer)
 {
 	struct kstat stat;
@@ -636,7 +651,15 @@ SYSCALL_DEFINE5(statx,
 		unsigned int, mask,
 		struct statx __user *, buffer)
 {
-	return do_statx(dfd, filename, flags, mask, buffer);
+	int ret;
+	struct filename *name;
+
+	name = getname_flags(filename, getname_statx_lookup_flags(flags), NULL);
+	ret = do_statx(dfd, name, flags, mask, buffer);
+	if (name)
+		putname(name);
+
+	return ret;
 }
 
 #ifdef CONFIG_COMPAT
-- 
2.30.2

[PATCH v1 2/2] io-uring: Copy path name during prepare stage for statx

[Stefan Roesch]

One of the key architectual tenets is to keep the parameters for
io-uring stable. After the call has been submitted, its value can
be changed. Unfortunaltely this is not the case for the current statx
implementation.

This changes replaces the const char * filename pointer in the io_statx
structure with a struct filename *. In addition it also creates the
filename object during the prepare phase.

With this change, the opcode also needs to invoke cleanup, so the
filename object gets freed after processing the request.

Signed-off-by: Stefan Roesch <shr@fb.com>
---
 fs/io_uring.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 2e04f718319d..86e2c8c4f216 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -642,7 +642,7 @@ struct io_statx {
 	int				dfd;
 	unsigned int			mask;
 	unsigned int			flags;
-	const char __user		*filename;
+	struct filename			*filename;
 	struct statx __user		*buffer;
 };
 
@@ -4721,6 +4721,8 @@ static int io_fadvise(struct io_kiocb *req, unsigned int issue_flags)
 
 static int io_statx_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
+	const char __user *path;
+
 	if (unlikely(req->ctx->flags & IORING_SETUP_IOPOLL))
 		return -EINVAL;
 	if (sqe->ioprio || sqe->buf_index || sqe->splice_fd_in)
@@ -4730,10 +4732,22 @@ static int io_statx_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 
 	req->statx.dfd = READ_ONCE(sqe->fd);
 	req->statx.mask = READ_ONCE(sqe->len);
-	req->statx.filename = u64_to_user_ptr(READ_ONCE(sqe->addr));
+	path = u64_to_user_ptr(READ_ONCE(sqe->addr));
 	req->statx.buffer = u64_to_user_ptr(READ_ONCE(sqe->addr2));
 	req->statx.flags = READ_ONCE(sqe->statx_flags);
 
+	req->statx.filename = getname_flags(path,
+					getname_statx_lookup_flags(req->statx.flags),
+					NULL);
+
+	if (IS_ERR(req->statx.filename)) {
+		int ret = PTR_ERR(req->statx.filename);
+
+		req->statx.filename = NULL;
+		return ret;
+	}
+
+	req->flags |= REQ_F_NEED_CLEANUP;
 	return 0;
 }
 
@@ -6709,6 +6723,10 @@ static void io_clean_op(struct io_kiocb *req)
 			putname(req->hardlink.oldpath);
 			putname(req->hardlink.newpath);
 			break;
+		case IORING_OP_STATX:
+			if (req->statx.filename)
+				putname(req->statx.filename);
+			break;
 		}
 	}
 	if ((req->flags & REQ_F_POLLED) && req->apoll) {
-- 
2.30.2

Re: [PATCH v1 1/2] fs: replace const char* parameter in vfs_statx and do_statx with struct filename

[Al Viro]

On Wed, Feb 09, 2022 at 11:03:44AM -0800, Stefan Roesch wrote:
> +	int ret;
> +	int statx_flags = flags | AT_NO_AUTOMOUNT;
> +	struct filename *name;
> +
> +	name = getname_flags(filename, getname_statx_lookup_flags(statx_flags), NULL);
> +	ret = vfs_statx(dfd, name, statx_flags, stat, STATX_BASIC_STATS);
> +	if (name)
> +		putname(name);

1) getname and friends return an error as ERR_PTR(-E...), not NULL
2) filename_lookup() et.al. treat ERR_PTR(-E...) as "fail with -E..."
3) putname(ERR_PTR(-E...)) is a no-op.

IOW, that if (name) putname(name); is unidiomatic and misleading.