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

[Stefan Roesch <shr@fb.com>]

On 1/5/22 5:22 AM, Christian Brauner wrote:
> 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):
> 

Christian, I made changes similar to the ones you recommended.
However I needed to introduce a union in the xattr_ctx structure.
For the setxattr function we require a const pointer and for getxattr
function we only require a pointer.

In addition it also needs changes in io_uring.c to pass in the context.

v12 has these changes.

> 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,