diff mbox series

[v10,2/5] fs: split off setxattr_copy and do_setxattr function from setxattr

Message ID 20211229203002.4110839-3-shr@fb.com (mailing list archive)
State New, archived
Headers show
Series io_uring: add xattr support | expand

Commit Message

Stefan Roesch Dec. 29, 2021, 8:29 p.m. UTC 
This splits of the setup part of the function
setxattr in its own dedicated function called
setxattr_copy. In addition it also exposes a
new function called do_setxattr for making the
setxattr call.

This makes it possible to call these two functions
from io_uring in the processing of an xattr request.

Signed-off-by: Stefan Roesch <shr@fb.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
---
 fs/internal.h | 21 +++++++++++++
 fs/xattr.c    | 82 ++++++++++++++++++++++++++++++++++++---------------
 2 files changed, 80 insertions(+), 23 deletions(-)

Comments

Al Viro Dec. 30, 2021, 1:15 a.m. UTC | #1 
On Wed, Dec 29, 2021 at 12:29:59PM -0800, Stefan Roesch wrote:
> +	if (ctx->size) {
> +		if (ctx->size > XATTR_SIZE_MAX)
>  			return -E2BIG;
> -		kvalue = kvmalloc(size, GFP_KERNEL);
> -		if (!kvalue)
> +
> +		ctx->kvalue = kvmalloc(ctx->size, GFP_KERNEL);
> +		if (!ctx->kvalue)
>  			return -ENOMEM;
> -		if (copy_from_user(kvalue, value, size)) {
> -			error = -EFAULT;
> -			goto out;
> +
> +		if (copy_from_user(ctx->kvalue, ctx->value, ctx->size)) {
> +			kvfree(ctx->kvalue);
> +			return -EFAULT;

BTW, what's wrong with using vmemdup_user() here?
Christian Brauner Dec. 30, 2021, 9:41 a.m. UTC | #2 
On Thu, Dec 30, 2021 at 01:15:10AM +0000, Al Viro wrote:
> On Wed, Dec 29, 2021 at 12:29:59PM -0800, Stefan Roesch wrote:
> > +	if (ctx->size) {
> > +		if (ctx->size > XATTR_SIZE_MAX)
> >  			return -E2BIG;
> > -		kvalue = kvmalloc(size, GFP_KERNEL);
> > -		if (!kvalue)
> > +
> > +		ctx->kvalue = kvmalloc(ctx->size, GFP_KERNEL);
> > +		if (!ctx->kvalue)
> >  			return -ENOMEM;
> > -		if (copy_from_user(kvalue, value, size)) {
> > -			error = -EFAULT;
> > -			goto out;
> > +
> > +		if (copy_from_user(ctx->kvalue, ctx->value, ctx->size)) {
> > +			kvfree(ctx->kvalue);
> > +			return -EFAULT;
> 
> BTW, what's wrong with using vmemdup_user() here?

Nothing? It's simply timing paired with that specific code not needing
to be touched:

- in 2005 that code was kmalloc(GFP_KERNEL) + copy_from_user()
- in 2009 it was changed to memdup_user(GFP_USER)
- in 2012 it was changed to kvmalloc(GFP_KERNEL) + copy_from_user()

In 2018 you added vmemdup_user() and noone has updated that codepath. :)
Stefan Roesch Dec. 30, 2021, 7:57 p.m. UTC | #3 
On 12/29/21 5:15 PM, Al Viro wrote:
> On Wed, Dec 29, 2021 at 12:29:59PM -0800, Stefan Roesch wrote:
>> +	if (ctx->size) {
>> +		if (ctx->size > XATTR_SIZE_MAX)
>>  			return -E2BIG;
>> -		kvalue = kvmalloc(size, GFP_KERNEL);
>> -		if (!kvalue)
>> +
>> +		ctx->kvalue = kvmalloc(ctx->size, GFP_KERNEL);
>> +		if (!ctx->kvalue)
>>  			return -ENOMEM;
>> -		if (copy_from_user(kvalue, value, size)) {
>> -			error = -EFAULT;
>> -			goto out;
>> +
>> +		if (copy_from_user(ctx->kvalue, ctx->value, ctx->size)) {
>> +			kvfree(ctx->kvalue);
>> +			return -EFAULT;
> 
> BTW, what's wrong with using vmemdup_user() here?

I was simply following the existing code. The next version will use the vmemdup_user function.
diff mbox series

Patch

diff --git a/fs/internal.h b/fs/internal.h
index afa60757d5f6..07487f29feb0 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -208,3 +208,24 @@  int vfs_getdents(struct file *file, struct linux_dirent64 __user *dirent,
   */
 extern int do_user_path_at_empty(int dfd, struct filename *filename,
 				unsigned int flags, struct path *path);
+
+ /*
+  * fs/xattr.c:
+  */
+struct xattr_name {
+	char name[XATTR_NAME_MAX + 1];
+};
+
+struct xattr_ctx {
+	/* Value of attribute */
+	const void __user *value;
+	void *kvalue;
+	size_t size;
+	/* Attribute name */
+	struct xattr_name *kname;
+	unsigned int flags;
+};
+
+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 5c8c5175b385..923ba944d20e 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -25,6 +25,8 @@ 
 
 #include <linux/uaccess.h>
 
+#include "internal.h"
+
 static const char *
 strcmp_prefix(const char *a, const char *a_prefix)
 {
@@ -539,43 +541,77 @@  EXPORT_SYMBOL_GPL(vfs_removexattr);
 /*
  * Extended attribute SET operations
  */
-static long
-setxattr(struct user_namespace *mnt_userns, struct dentry *d,
-	 const char __user *name, const void __user *value, size_t size,
-	 int flags)
+
+int setxattr_copy(const char __user *name, struct xattr_ctx *ctx)
 {
 	int error;
-	void *kvalue = NULL;
-	char kname[XATTR_NAME_MAX + 1];
 
-	if (flags & ~(XATTR_CREATE|XATTR_REPLACE))
+	if (ctx->flags & ~(XATTR_CREATE|XATTR_REPLACE))
 		return -EINVAL;
 
-	error = strncpy_from_user(kname, name, sizeof(kname));
-	if (error == 0 || error == sizeof(kname))
-		error = -ERANGE;
+	error = strncpy_from_user(ctx->kname->name, name,
+				sizeof(ctx->kname->name));
+	if (error == 0 || error == sizeof(ctx->kname->name))
+		return  -ERANGE;
 	if (error < 0)
 		return error;
 
-	if (size) {
-		if (size > XATTR_SIZE_MAX)
+	if (ctx->size) {
+		if (ctx->size > XATTR_SIZE_MAX)
 			return -E2BIG;
-		kvalue = kvmalloc(size, GFP_KERNEL);
-		if (!kvalue)
+
+		ctx->kvalue = kvmalloc(ctx->size, GFP_KERNEL);
+		if (!ctx->kvalue)
 			return -ENOMEM;
-		if (copy_from_user(kvalue, value, size)) {
-			error = -EFAULT;
-			goto out;
+
+		if (copy_from_user(ctx->kvalue, ctx->value, ctx->size)) {
+			kvfree(ctx->kvalue);
+			return -EFAULT;
 		}
-		if ((strcmp(kname, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
-		    (strcmp(kname, XATTR_NAME_POSIX_ACL_DEFAULT) == 0))
-			posix_acl_fix_xattr_from_user(mnt_userns, kvalue, size);
 	}
 
-	error = vfs_setxattr(mnt_userns, d, kname, kvalue, size, flags);
-out:
-	kvfree(kvalue);
+	return 0;
+}
+
+static void setxattr_convert(struct user_namespace *mnt_userns,
+			struct xattr_ctx *ctx)
+{
+	if (ctx->size &&
+		((strcmp(ctx->kname->name, XATTR_NAME_POSIX_ACL_ACCESS) == 0) ||
+		(strcmp(ctx->kname->name, XATTR_NAME_POSIX_ACL_DEFAULT) == 0)))
+		posix_acl_fix_xattr_from_user(mnt_userns, ctx->kvalue, ctx->size);
+}
+
+int do_setxattr(struct user_namespace *mnt_userns, struct dentry *dentry,
+		struct xattr_ctx *ctx)
+{
+	setxattr_convert(mnt_userns, ctx);
+	return vfs_setxattr(mnt_userns, dentry, ctx->kname->name,
+			ctx->kvalue, ctx->size, ctx->flags);
+}
+
+static long
+setxattr(struct user_namespace *mnt_userns, struct dentry *d,
+	const char __user *name, const void __user *value, size_t size,
+	int flags)
+{
+	struct xattr_name kname;
+	struct xattr_ctx ctx = {
+		.value    = value,
+		.kvalue   = NULL,
+		.size     = size,
+		.kname    = &kname,
+		.flags    = flags,
+	};
+	int error;
+
+	error = setxattr_copy(name, &ctx);
+	if (error)
+		return error;
+
+	error = do_setxattr(mnt_userns, d, &ctx);
 
+	kvfree(ctx.kvalue);
 	return error;
 }