Re: [PATCH v11 2/4] fs: split off do_getxattr from getxattr

[Christian Brauner <christian.brauner@ubuntu.com>]

On Tue, Jan 04, 2022 at 11:09:34AM -0800, Stefan Roesch wrote:
> This splits off do_getxattr function from the getxattr
> function. This will allow io_uring to call it from its
> io worker.
> 
> Signed-off-by: Stefan Roesch <shr@fb.com>
> Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
> ---
>  fs/internal.h |  7 +++++++
>  fs/xattr.c    | 32 ++++++++++++++++++++------------
>  2 files changed, 27 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/internal.h b/fs/internal.h
> index 00c98b0cd634..942b2005a2be 100644
> --- a/fs/internal.h
> +++ b/fs/internal.h
> @@ -220,6 +220,13 @@ struct xattr_ctx {
>  	unsigned int flags;
>  };
>  
> +
> +ssize_t do_getxattr(struct user_namespace *mnt_userns,
> +		    struct dentry *d,
> +		    const char *kname,
> +		    void __user *value,
> +		    size_t size);
> +
>  int setxattr_copy(const char __user *name, struct xattr_ctx *ctx);
>  int do_setxattr(struct user_namespace *mnt_userns, struct dentry *dentry,
>  		struct xattr_ctx *ctx);
> diff --git a/fs/xattr.c b/fs/xattr.c
> index dec7ac3e0e89..7f2b805ed56c 100644
> --- a/fs/xattr.c
> +++ b/fs/xattr.c
> @@ -675,19 +675,12 @@ SYSCALL_DEFINE5(fsetxattr, int, fd, const char __user *, name,
>  /*
>   * Extended attribute GET operations
>   */
> -static ssize_t
> -getxattr(struct user_namespace *mnt_userns, struct dentry *d,
> -	 const char __user *name, void __user *value, size_t size)
> +ssize_t
> +do_getxattr(struct user_namespace *mnt_userns, struct dentry *d,
> +	const char *kname, void __user *value, size_t size)
>  {
> -	ssize_t error;
>  	void *kvalue = NULL;
> -	char kname[XATTR_NAME_MAX + 1];
> -
> -	error = strncpy_from_user(kname, name, sizeof(kname));
> -	if (error == 0 || error == sizeof(kname))
> -		error = -ERANGE;
> -	if (error < 0)
> -		return error;
> +	ssize_t error;
>  
>  	if (size) {
>  		if (size > XATTR_SIZE_MAX)
> @@ -711,10 +704,25 @@ getxattr(struct user_namespace *mnt_userns, struct dentry *d,
>  	}
>  
>  	kvfree(kvalue);
> -
>  	return error;
>  }
>  
> +static ssize_t
> +getxattr(struct user_namespace *mnt_userns, struct dentry *d,
> +	 const char __user *name, void __user *value, size_t size)
> +{
> +	ssize_t error;
> +	struct xattr_name kname;
> +
> +	error = strncpy_from_user(kname.name, name, sizeof(kname.name));
> +	if (error == 0 || error == sizeof(kname.name))
> +		error = -ERANGE;
> +	if (error < 0)
> +		return error;
> +
> +	return do_getxattr(mnt_userns, d, kname.name, value, size);
> +}

Fwiw, this could have the same signature as do_setxattr(). So sm along
the lines of (completely untested):

Subject: [PATCH] UNTESTED

---
 fs/internal.h |  8 ++------
 fs/xattr.c    | 36 ++++++++++++++++++++++--------------
 2 files changed, 24 insertions(+), 20 deletions(-)

diff --git a/fs/internal.h b/fs/internal.h
index 942b2005a2be..d2332496724b 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -220,12 +220,8 @@ struct xattr_ctx {
 	unsigned int flags;
 };
 
-
-ssize_t do_getxattr(struct user_namespace *mnt_userns,
-		    struct dentry *d,
-		    const char *kname,
-		    void __user *value,
-		    size_t size);
+ssize_t do_getxattr(struct user_namespace *mnt_userns, struct dentry *dentry,
+		    struct xattr_ctx *ctx);
 
 int setxattr_copy(const char __user *name, struct xattr_ctx *ctx);
 int do_setxattr(struct user_namespace *mnt_userns, struct dentry *dentry,
diff --git a/fs/xattr.c b/fs/xattr.c
index 7f2b805ed56c..52bcfe149a9f 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -675,35 +675,34 @@ SYSCALL_DEFINE5(fsetxattr, int, fd, const char __user *, name,
 /*
  * Extended attribute GET operations
  */
-ssize_t
-do_getxattr(struct user_namespace *mnt_userns, struct dentry *d,
-	const char *kname, void __user *value, size_t size)
+ssize_t do_getxattr(struct user_namespace *mnt_userns, struct dentry *dentry,
+		    struct xattr_ctx *ctx)
+
 {
-	void *kvalue = NULL;
 	ssize_t error;
+	char *kname = ctx->kname.name;
 
-	if (size) {
-		if (size > XATTR_SIZE_MAX)
-			size = XATTR_SIZE_MAX;
-		kvalue = kvzalloc(size, GFP_KERNEL);
-		if (!kvalue)
+	if (ctx->size) {
+		if (ctx->size > XATTR_SIZE_MAX)
+			ctx->size = XATTR_SIZE_MAX;
+		ctx->kvalue = kvzalloc(ctx->size, GFP_KERNEL);
+		if (!ctx->kvalue)
 			return -ENOMEM;
 	}
 
-	error = vfs_getxattr(mnt_userns, d, kname, kvalue, size);
+	error = vfs_getxattr(mnt_userns, d, kname, ctx->kvalue, ctx->size);
 	if (error > 0) {
 		if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
 		    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))
 			posix_acl_fix_xattr_to_user(mnt_userns, kvalue, error);
-		if (size && copy_to_user(value, kvalue, error))
+		if (ctx->size && copy_to_user(value, kvalue, error))
 			error = -EFAULT;
-	} else if (error == -ERANGE && size >= XATTR_SIZE_MAX) {
+	} else if (error == -ERANGE && ctx->size >= XATTR_SIZE_MAX) {
 		/* The file system tried to returned a value bigger
 		   than XATTR_SIZE_MAX bytes. Not possible. */
 		error = -E2BIG;
 	}
 
-	kvfree(kvalue);
 	return error;
 }
 
@@ -713,6 +712,12 @@ getxattr(struct user_namespace *mnt_userns, struct dentry *d,
 {
 	ssize_t error;
 	struct xattr_name kname;
+	struct xattr_ctx ctx = {
+		.value    = value,
+		.kvalue   = NULL,
+		.size     = size,
+		.kname    = &kname,
+	};
 
 	error = strncpy_from_user(kname.name, name, sizeof(kname.name));
 	if (error == 0 || error == sizeof(kname.name))
@@ -720,7 +725,10 @@ getxattr(struct user_namespace *mnt_userns, struct dentry *d,
 	if (error < 0)
 		return error;
 
-	return do_getxattr(mnt_userns, d, kname.name, value, size);
+	error = do_getxattr(mnt_userns, d, &ctx);
+
+	kvfree(ctx.kvalue);
+	return error;
 }
 
 static ssize_t path_getxattr(const char __user *pathname,
-- 
2.32.0