Re: [PATCH v6 6/6] fs: introduce file_getattr and file_setattr syscalls

From: Christian Brauner <brauner@kernel.org>
Date: 2025-07-01 12:34:54
Also in: linux-fsdevel, linux-xfs, lkml, selinux

On Mon, Jun 30, 2025 at 06:20:16PM +0200, Andrey Albershteyn wrote:

quoted hunk ↗ jump to hunk

From: Andrey Albershteyn <redacted>

Introduce file_getattr() and file_setattr() syscalls to manipulate inode
extended attributes. The syscalls takes pair of file descriptor and
pathname. Then it operates on inode opened accroding to openat()
semantics. The struct fsx_fileattr is passed to obtain/change extended
attributes.

This is an alternative to FS_IOC_FSSETXATTR ioctl with a difference
that file don't need to be open as we can reference it with a path
instead of fd. By having this we can manipulated inode extended
attributes not only on regular files but also on special ones. This
is not possible with FS_IOC_FSSETXATTR ioctl as with special files
we can not call ioctl() directly on the filesystem inode using fd.

This patch adds two new syscalls which allows userspace to get/set
extended inode attributes on special files by using parent directory
and a path - *at() like syscall.

CC: linux-api@vger.kernel.org
CC: linux-fsdevel@vger.kernel.org
CC: linux-xfs@vger.kernel.org
Signed-off-by: Andrey Albershteyn <aalbersh@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
---
 arch/alpha/kernel/syscalls/syscall.tbl      |   2 +
 arch/arm/tools/syscall.tbl                  |   2 +
 arch/arm64/tools/syscall_32.tbl             |   2 +
 arch/m68k/kernel/syscalls/syscall.tbl       |   2 +
 arch/microblaze/kernel/syscalls/syscall.tbl |   2 +
 arch/mips/kernel/syscalls/syscall_n32.tbl   |   2 +
 arch/mips/kernel/syscalls/syscall_n64.tbl   |   2 +
 arch/mips/kernel/syscalls/syscall_o32.tbl   |   2 +
 arch/parisc/kernel/syscalls/syscall.tbl     |   2 +
 arch/powerpc/kernel/syscalls/syscall.tbl    |   2 +
 arch/s390/kernel/syscalls/syscall.tbl       |   2 +
 arch/sh/kernel/syscalls/syscall.tbl         |   2 +
 arch/sparc/kernel/syscalls/syscall.tbl      |   2 +
 arch/x86/entry/syscalls/syscall_32.tbl      |   2 +
 arch/x86/entry/syscalls/syscall_64.tbl      |   2 +
 arch/xtensa/kernel/syscalls/syscall.tbl     |   2 +
 fs/file_attr.c                              | 148 ++++++++++++++++++++++++++++
 include/linux/syscalls.h                    |   6 ++
 include/uapi/asm-generic/unistd.h           |   8 +-
 include/uapi/linux/fs.h                     |  18 ++++
 scripts/syscall.tbl                         |   2 +
 21 files changed, 213 insertions(+), 1 deletion(-)

diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
index 2dd6340de6b4..16dca28ebf17 100644
--- a/arch/alpha/kernel/syscalls/syscall.tbl
+++ b/arch/alpha/kernel/syscalls/syscall.tbl

@@ -507,3 +507,5 @@
 575	common	listxattrat			sys_listxattrat
 576	common	removexattrat			sys_removexattrat
 577	common	open_tree_attr			sys_open_tree_attr
+578	common	file_getattr			sys_file_getattr
+579	common	file_setattr			sys_file_setattr

diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
index 27c1d5ebcd91..b07e699aaa3c 100644
--- a/arch/arm/tools/syscall.tbl
+++ b/arch/arm/tools/syscall.tbl

@@ -482,3 +482,5 @@
 465	common	listxattrat			sys_listxattrat
 466	common	removexattrat			sys_removexattrat
 467	common	open_tree_attr			sys_open_tree_attr
+468	common	file_getattr			sys_file_getattr
+469	common	file_setattr			sys_file_setattr

diff --git a/arch/arm64/tools/syscall_32.tbl b/arch/arm64/tools/syscall_32.tbl
index 0765b3a8d6d6..8d9088bc577d 100644
--- a/arch/arm64/tools/syscall_32.tbl
+++ b/arch/arm64/tools/syscall_32.tbl

@@ -479,3 +479,5 @@
 465	common	listxattrat			sys_listxattrat
 466	common	removexattrat			sys_removexattrat
 467	common	open_tree_attr			sys_open_tree_attr
+468	common	file_getattr			sys_file_getattr
+469	common	file_setattr			sys_file_setattr

diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
index 9fe47112c586..f41d38dfbf13 100644
--- a/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl

@@ -467,3 +467,5 @@
 465	common	listxattrat			sys_listxattrat
 466	common	removexattrat			sys_removexattrat
 467	common	open_tree_attr			sys_open_tree_attr
+468	common	file_getattr			sys_file_getattr
+469	common	file_setattr			sys_file_setattr

diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
index 7b6e97828e55..580af574fe73 100644
--- a/arch/microblaze/kernel/syscalls/syscall.tbl
+++ b/arch/microblaze/kernel/syscalls/syscall.tbl

@@ -473,3 +473,5 @@
 465	common	listxattrat			sys_listxattrat
 466	common	removexattrat			sys_removexattrat
 467	common	open_tree_attr			sys_open_tree_attr
+468	common	file_getattr			sys_file_getattr
+469	common	file_setattr			sys_file_setattr

diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl
index aa70e371bb54..d824ffe9a014 100644
--- a/arch/mips/kernel/syscalls/syscall_n32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n32.tbl

@@ -406,3 +406,5 @@
 465	n32	listxattrat			sys_listxattrat
 466	n32	removexattrat			sys_removexattrat
 467	n32	open_tree_attr			sys_open_tree_attr
+468	n32	file_getattr			sys_file_getattr
+469	n32	file_setattr			sys_file_setattr

diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl
index 1e8c44c7b614..7a7049c2c307 100644
--- a/arch/mips/kernel/syscalls/syscall_n64.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n64.tbl

@@ -382,3 +382,5 @@
 465	n64	listxattrat			sys_listxattrat
 466	n64	removexattrat			sys_removexattrat
 467	n64	open_tree_attr			sys_open_tree_attr
+468	n64	file_getattr			sys_file_getattr
+469	n64	file_setattr			sys_file_setattr

diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl
index 114a5a1a6230..d330274f0601 100644
--- a/arch/mips/kernel/syscalls/syscall_o32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_o32.tbl

@@ -455,3 +455,5 @@
 465	o32	listxattrat			sys_listxattrat
 466	o32	removexattrat			sys_removexattrat
 467	o32	open_tree_attr			sys_open_tree_attr
+468	o32	file_getattr			sys_file_getattr
+469	o32	file_setattr			sys_file_setattr

diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
index 94df3cb957e9..88a788a7b18d 100644
--- a/arch/parisc/kernel/syscalls/syscall.tbl
+++ b/arch/parisc/kernel/syscalls/syscall.tbl

@@ -466,3 +466,5 @@
 465	common	listxattrat			sys_listxattrat
 466	common	removexattrat			sys_removexattrat
 467	common	open_tree_attr			sys_open_tree_attr
+468	common	file_getattr			sys_file_getattr
+469	common	file_setattr			sys_file_setattr

diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
index 9a084bdb8926..b453e80dfc00 100644
--- a/arch/powerpc/kernel/syscalls/syscall.tbl
+++ b/arch/powerpc/kernel/syscalls/syscall.tbl

@@ -558,3 +558,5 @@
 465	common	listxattrat			sys_listxattrat
 466	common	removexattrat			sys_removexattrat
 467	common	open_tree_attr			sys_open_tree_attr
+468	common	file_getattr			sys_file_getattr
+469	common	file_setattr			sys_file_setattr

diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
index a4569b96ef06..8a6744d658db 100644
--- a/arch/s390/kernel/syscalls/syscall.tbl
+++ b/arch/s390/kernel/syscalls/syscall.tbl

@@ -470,3 +470,5 @@
 465  common	listxattrat		sys_listxattrat			sys_listxattrat
 466  common	removexattrat		sys_removexattrat		sys_removexattrat
 467  common	open_tree_attr		sys_open_tree_attr		sys_open_tree_attr
+468  common	file_getattr		sys_file_getattr		sys_file_getattr
+469  common	file_setattr		sys_file_setattr		sys_file_setattr

diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
index 52a7652fcff6..5e9c9eff5539 100644
--- a/arch/sh/kernel/syscalls/syscall.tbl
+++ b/arch/sh/kernel/syscalls/syscall.tbl

@@ -471,3 +471,5 @@
 465	common	listxattrat			sys_listxattrat
 466	common	removexattrat			sys_removexattrat
 467	common	open_tree_attr			sys_open_tree_attr
+468	common	file_getattr			sys_file_getattr
+469	common	file_setattr			sys_file_setattr

diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
index 83e45eb6c095..ebb7d06d1044 100644
--- a/arch/sparc/kernel/syscalls/syscall.tbl
+++ b/arch/sparc/kernel/syscalls/syscall.tbl

@@ -513,3 +513,5 @@
 465	common	listxattrat			sys_listxattrat
 466	common	removexattrat			sys_removexattrat
 467	common	open_tree_attr			sys_open_tree_attr
+468	common	file_getattr			sys_file_getattr
+469	common	file_setattr			sys_file_setattr

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index ac007ea00979..4877e16da69a 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl

@@ -473,3 +473,5 @@
 465	i386	listxattrat		sys_listxattrat
 466	i386	removexattrat		sys_removexattrat
 467	i386	open_tree_attr		sys_open_tree_attr
+468	i386	file_getattr		sys_file_getattr
+469	i386	file_setattr		sys_file_setattr

diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index cfb5ca41e30d..92cf0fe2291e 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl

@@ -391,6 +391,8 @@
 465	common	listxattrat		sys_listxattrat
 466	common	removexattrat		sys_removexattrat
 467	common	open_tree_attr		sys_open_tree_attr
+468	common	file_getattr		sys_file_getattr
+469	common	file_setattr		sys_file_setattr
 
 #
 # Due to a historical design error, certain syscalls are numbered differently

diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl
index f657a77314f8..374e4cb788d8 100644
--- a/arch/xtensa/kernel/syscalls/syscall.tbl
+++ b/arch/xtensa/kernel/syscalls/syscall.tbl

@@ -438,3 +438,5 @@
 465	common	listxattrat			sys_listxattrat
 466	common	removexattrat			sys_removexattrat
 467	common	open_tree_attr			sys_open_tree_attr
+468	common	file_getattr			sys_file_getattr
+469	common	file_setattr			sys_file_setattr

diff --git a/fs/file_attr.c b/fs/file_attr.c
index 62f08872d4ad..fda9d847eee5 100644
--- a/fs/file_attr.c
+++ b/fs/file_attr.c

@@ -3,6 +3,10 @@
 #include <linux/security.h>
 #include <linux/fscrypt.h>
 #include <linux/fileattr.h>
+#include <linux/syscalls.h>
+#include <linux/namei.h>
+
+#include "internal.h"
 
 /**
  * fileattr_fill_xflags - initialize fileattr with xflags

@@ -89,6 +93,19 @@ int vfs_fileattr_get(struct dentry *dentry, struct fileattr *fa)
 }
 EXPORT_SYMBOL(vfs_fileattr_get);
 
+static void fileattr_to_fsx_fileattr(const struct fileattr *fa,
+				     struct fsx_fileattr *fsx)
+{
+	__u32 mask = FS_XFLAGS_MASK;
+
+	memset(fsx, 0, sizeof(struct fsx_fileattr));

Fwiw, what also works is:

*fsx = (struct fsx_fileattr){
	.fsx_xflags	= fa->fsx_xflags & mask,
	.fsx_extsize	= fa->fsx_extsize,
	.fsx_nextents	= fa->fsx_nextents,
	.fsx_projid	= fa->fsx_projid,
	.fsx_cowextsize	= fa->fsx_cowextsize,
}

avoiding the memset(). Anyway, all minor nits.

quoted hunk ↗ jump to hunk

+	fsx->fsx_xflags = fa->fsx_xflags & mask;
+	fsx->fsx_extsize = fa->fsx_extsize;
+	fsx->fsx_nextents = fa->fsx_nextents;
+	fsx->fsx_projid = fa->fsx_projid;
+	fsx->fsx_cowextsize = fa->fsx_cowextsize;
+}
+
 /**
  * copy_fsxattr_to_user - copy fsxattr to userspace.
  * @fa:		fileattr pointer

@@ -115,6 +132,23 @@ int copy_fsxattr_to_user(const struct fileattr *fa, struct fsxattr __user *ufa)
 }
 EXPORT_SYMBOL(copy_fsxattr_to_user);
 
+static int fsx_fileattr_to_fileattr(const struct fsx_fileattr *fsx,
+				    struct fileattr *fa)
+{
+	__u32 mask = FS_XFLAGS_MASK;
+
+	if (fsx->fsx_xflags & ~mask)
+		return -EINVAL;
+
+	fileattr_fill_xflags(fa, fsx->fsx_xflags);
+	fa->fsx_xflags &= ~FS_XFLAG_RDONLY_MASK;
+	fa->fsx_extsize = fsx->fsx_extsize;
+	fa->fsx_projid = fsx->fsx_projid;
+	fa->fsx_cowextsize = fsx->fsx_cowextsize;
+
+	return 0;
+}
+
 static int copy_fsxattr_from_user(struct fileattr *fa,
 				  struct fsxattr __user *ufa)
 {
@@ -343,3 +377,117 @@ int ioctl_fssetxattr(struct file *file, void __user *argp)
 	return err;
 }
 EXPORT_SYMBOL(ioctl_fssetxattr);
+
+SYSCALL_DEFINE5(file_getattr, int, dfd, const char __user *, filename,
+		struct fsx_fileattr __user *, ufsx, size_t, usize,
+		unsigned int, at_flags)
+{
+	struct fileattr fa;
+	struct path filepath __free(path_put) = {};
+	int error;
+	unsigned int lookup_flags = 0;
+	struct filename *name __free(putname) = NULL;

Fwiw, cleanup guards should always be grouped together at the top like:

struct path filepath __free(path_put) = {};
struct filename *name __free(putname) = NULL;
struct fileattr fa;
int error;
unsigned int lookup_flags = 0;

This makes it easy to spot them when reading a function with multiple
variables on top.

+	struct fsx_fileattr fsx;

+	struct fsx_fileattr fsx;
+
+	BUILD_BUG_ON(sizeof(struct fsx_fileattr) < FSX_FILEATTR_SIZE_VER0);
+	BUILD_BUG_ON(sizeof(struct fsx_fileattr) != FSX_FILEATTR_SIZE_LATEST);
+
+	if ((at_flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
+		return -EINVAL;
+
+	if (!(at_flags & AT_SYMLINK_NOFOLLOW))
+		lookup_flags |= LOOKUP_FOLLOW;
+
+	if (usize > PAGE_SIZE)
+		return -E2BIG;
+
+	if (usize < FSX_FILEATTR_SIZE_VER0)
+		return -EINVAL;
+
+	name = getname_maybe_null(filename, at_flags);
+	if (IS_ERR(name))
+		return PTR_ERR(name);
+
+	if (!name && dfd >= 0) {
+		CLASS(fd, f)(dfd);
+
+		filepath = fd_file(f)->f_path;
+		path_get(&filepath);
+	} else {
+		error = filename_lookup(dfd, name, lookup_flags, &filepath,
+					NULL);
+		if (error)
+			return error;
+	}
+
+	error = vfs_fileattr_get(filepath.dentry, &fa);
+	if (error)
+		return error;
+
+	fileattr_to_fsx_fileattr(&fa, &fsx);
+	error = copy_struct_to_user(ufsx, usize, &fsx,
+				    sizeof(struct fsx_fileattr), NULL);
+
+	return error;
+}
+
+SYSCALL_DEFINE5(file_setattr, int, dfd, const char __user *, filename,
+		struct fsx_fileattr __user *, ufsx, size_t, usize,
+		unsigned int, at_flags)
+{
+	struct fileattr fa;
+	struct path filepath __free(path_put) = {};
+	int error;
+	unsigned int lookup_flags = 0;
+	struct filename *name __free(putname) = NULL;
+	struct fsx_fileattr fsx;
+
+	BUILD_BUG_ON(sizeof(struct fsx_fileattr) < FSX_FILEATTR_SIZE_VER0);
+	BUILD_BUG_ON(sizeof(struct fsx_fileattr) != FSX_FILEATTR_SIZE_LATEST);
+
+	if ((at_flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
+		return -EINVAL;
+
+	if (!(at_flags & AT_SYMLINK_NOFOLLOW))
+		lookup_flags |= LOOKUP_FOLLOW;
+
+	if (usize > PAGE_SIZE)
+		return -E2BIG;
+
+	if (usize < FSX_FILEATTR_SIZE_VER0)
+		return -EINVAL;
+
+	error = copy_struct_from_user(&fsx, sizeof(struct fsx_fileattr), ufsx,
+				      usize);
+	if (error)
+		return error;
+
+	error = fsx_fileattr_to_fileattr(&fsx, &fa);
+	if (error)
+		return error;
+
+	name = getname_maybe_null(filename, at_flags);
+	if (IS_ERR(name))
+		return PTR_ERR(name);
+
+	if (!name && dfd >= 0) {
+		CLASS(fd, f)(dfd);
+
+		filepath = fd_file(f)->f_path;
+		path_get(&filepath);
+	} else {
+		error = filename_lookup(dfd, name, lookup_flags, &filepath,
+					NULL);
+		if (error)
+			return error;
+	}
+
+	error = mnt_want_write(filepath.mnt);
+	if (!error) {
+		error = vfs_fileattr_set(mnt_idmap(filepath.mnt),
+					 filepath.dentry, &fa);
+		mnt_drop_write(filepath.mnt);
+	}

Note-to-self: I really want scoped_guard()s for mnt_want_write() going forward...

quoted hunk ↗ jump to hunk

+
+	return error;
+}

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index e5603cc91963..179acbe28fec 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h

@@ -371,6 +371,12 @@ asmlinkage long sys_removexattrat(int dfd, const char __user *path,
 asmlinkage long sys_lremovexattr(const char __user *path,
 				 const char __user *name);
 asmlinkage long sys_fremovexattr(int fd, const char __user *name);
+asmlinkage long sys_file_getattr(int dfd, const char __user *filename,
+				 struct fsx_fileattr __user *ufsx, size_t usize,
+				 unsigned int at_flags);
+asmlinkage long sys_file_setattr(int dfd, const char __user *filename,
+				 struct fsx_fileattr __user *ufsx, size_t usize,
+				 unsigned int at_flags);
 asmlinkage long sys_getcwd(char __user *buf, unsigned long size);
 asmlinkage long sys_eventfd2(unsigned int count, int flags);
 asmlinkage long sys_epoll_create1(int flags);

diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index 2892a45023af..04e0077fb4c9 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h

@@ -852,8 +852,14 @@ __SYSCALL(__NR_removexattrat, sys_removexattrat)
 #define __NR_open_tree_attr 467
 __SYSCALL(__NR_open_tree_attr, sys_open_tree_attr)
 
+/* fs/inode.c */
+#define __NR_file_getattr 468
+__SYSCALL(__NR_file_getattr, sys_file_getattr)
+#define __NR_file_setattr 469
+__SYSCALL(__NR_file_setattr, sys_file_setattr)
+
 #undef __NR_syscalls
-#define __NR_syscalls 468
+#define __NR_syscalls 470
 
 /*
  * 32 bit systems traditionally used different

diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index 0098b0ce8ccb..0784f2033ba4 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h

@@ -148,6 +148,24 @@ struct fsxattr {
 	unsigned char	fsx_pad[8];
 };
 
+/*
+ * Variable size structure for file_[sg]et_attr().
+ *
+ * Note. This is alternative to the structure 'struct fileattr'/'struct fsxattr'.
+ * As this structure is passed to/from userspace with its size, this can
+ * be versioned based on the size.
+ */
+struct fsx_fileattr {
+	__u32	fsx_xflags;	/* xflags field value (get/set) */
+	__u32	fsx_extsize;	/* extsize field value (get/set)*/
+	__u32	fsx_nextents;	/* nextents field value (get)   */
+	__u32	fsx_projid;	/* project identifier (get/set) */
+	__u32	fsx_cowextsize;	/* CoW extsize field value (get/set) */

This misses a:

__u32 __spare;

so there's no holes in the struct. :)

quoted hunk ↗ jump to hunk

+};
+
+#define FSX_FILEATTR_SIZE_VER0 20
+#define FSX_FILEATTR_SIZE_LATEST FSX_FILEATTR_SIZE_VER0
+
 /*
  * Flags for the fsx_xflags field
  */

diff --git a/scripts/syscall.tbl b/scripts/syscall.tbl
index 580b4e246aec..d1ae5e92c615 100644
--- a/scripts/syscall.tbl
+++ b/scripts/syscall.tbl

@@ -408,3 +408,5 @@
 465	common	listxattrat			sys_listxattrat
 466	common	removexattrat			sys_removexattrat
 467	common	open_tree_attr			sys_open_tree_attr
+468	common	file_getattr			sys_file_getattr
+469	common	file_setattr			sys_file_setattr

-- 
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