[PATCH v3] fs: introduce getfsxattrat and setfsxattrat syscalls

Andrey Albershteyn
2025-02-11T17:23:29Z

From: Andrey Albershteyn <aalbersh@redhat.com>

Introduce getfsxattrat and setfsxattrat syscalls to manipulate inode
extended attributes/flags. The syscalls take parent directory fd and
path to the child together with struct fsxattr.

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.

Also, as vfs_fileattr_set() is now will be called on special files
too, let's forbid any other attributes except projid and nextents
(symlink can have an extent).

CC: linux-api@vger.kernel.org
CC: linux-fsdevel@vger.kernel.org
CC: linux-xfs@vger.kernel.org
Signed-off-by: Andrey Albershteyn <aalbersh@redhat.com>
---
v1:
https://lore.kernel.org/linuxppc-dev/20250109174540.893098-1-aalbersh@kernel.org/

Previous discussion:
https://lore.kernel.org/linux-xfs/20240520164624.665269-2-aalbersh@redhat.com/

XFS has project quotas which could be attached to a directory. All
new inodes in these directories inherit project ID set on parent
directory.

The project is created from userspace by opening and calling
FS_IOC_FSSETXATTR on each inode. This is not possible for special
files such as FIFO, SOCK, BLK etc. Therefore, some inodes are left
with empty project ID. Those inodes then are not shown in the quota
accounting but still exist in the directory. Moreover, in the case
when special files are created in the directory with already
existing project quota, these inode inherit extended attributes.
This than leaves them with these attributes without the possibility
to clear them out. This, in turn, prevents userspace from
re-creating quota project on these existing files.
---
Changes in v3:
- Remove unnecessary "dfd is dir" check as it checked in user_path_at()
- Remove unnecessary "same filesystem" check
- Use CLASS() instead of directly calling fdget/fdput
- Link to v2: https://lore.kernel.org/r/20250122-xattrat-syscall-v2-1-5b360d4fbcb2@kernel.org
---
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/inode.c | 75 +++++++++++++++++++++++++++++
fs/ioctl.c | 16 +++++-
include/linux/fileattr.h | 1 +
include/linux/syscalls.h | 4 ++
include/uapi/asm-generic/unistd.h | 8 ++-
21 files changed, 133 insertions(+), 3 deletions(-)

diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
index c59d53d6d3f3490f976ca179ddfe02e69265ae4d..4b9e687494c16b60c6fd6ca1dc4d6564706a7e25 100644
--- a/arch/alpha/kernel/syscalls/syscall.tbl
+++ b/arch/alpha/kernel/syscalls/syscall.tbl
@@ -506,3 +506,5 @@
574 common getxattrat sys_getxattrat
575 common listxattrat sys_listxattrat
576 common removexattrat sys_removexattrat
+577 common getfsxattrat sys_getfsxattrat
+578 common setfsxattrat sys_setfsxattrat
diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
index 49eeb2ad8dbd8e074c6240417693f23fb328afa8..66466257f3c2debb3e2299f0b608c6740c98cab2 100644
--- a/arch/arm/tools/syscall.tbl
+++ b/arch/arm/tools/syscall.tbl
@@ -481,3 +481,5 @@
464 common getxattrat sys_getxattrat
465 common listxattrat sys_listxattrat
466 common removexattrat sys_removexattrat
+467 common getfsxattrat sys_getfsxattrat
+468 common setfsxattrat sys_setfsxattrat
diff --git a/arch/arm64/tools/syscall_32.tbl b/arch/arm64/tools/syscall_32.tbl
index 69a829912a05eb8a3e21ed701d1030e31c0148bc..9c516118b154811d8d11d5696f32817430320dbf 100644
--- a/arch/arm64/tools/syscall_32.tbl
+++ b/arch/arm64/tools/syscall_32.tbl
@@ -478,3 +478,5 @@
464 common getxattrat sys_getxattrat
465 common listxattrat sys_listxattrat
466 common removexattrat sys_removexattrat
+467 common getfsxattrat sys_getfsxattrat
+468 common setfsxattrat sys_setfsxattrat
diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
index f5ed71f1910d09769c845c2d062d99ee0449437c..159476387f394a92ee5e29db89b118c630372db2 100644
--- a/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl
@@ -466,3 +466,5 @@
464 common getxattrat sys_getxattrat
465 common listxattrat sys_listxattrat
466 common removexattrat sys_removexattrat
+467 common getfsxattrat sys_getfsxattrat
+468 common setfsxattrat sys_setfsxattrat
diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
index 680f568b77f2cbefc3eacb2517f276041f229b1e..a6d59ee740b58cacf823702003cf9bad17c0d3b7 100644
--- a/arch/microblaze/kernel/syscalls/syscall.tbl
+++ b/arch/microblaze/kernel/syscalls/syscall.tbl
@@ -472,3 +472,5 @@
464 common getxattrat sys_getxattrat
465 common listxattrat sys_listxattrat
466 common removexattrat sys_removexattrat
+467 common getfsxattrat sys_getfsxattrat
+468 common setfsxattrat sys_setfsxattrat
diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl
index 0b9b7e25b69ad592642f8533bee9ccfe95ce9626..cfe38fcebe1a0279e11751378d3e71c5ec6b6569 100644
--- a/arch/mips/kernel/syscalls/syscall_n32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
@@ -405,3 +405,5 @@
464 n32 getxattrat sys_getxattrat
465 n32 listxattrat sys_listxattrat
466 n32 removexattrat sys_removexattrat
+467 n32 getfsxattrat sys_getfsxattrat
+468 n32 setfsxattrat sys_setfsxattrat
diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl
index c844cd5cda620b2809a397cdd6f4315ab6a1bfe2..29a0c5974d1aa2f01e33edc0252d75fb97abe230 100644
--- a/arch/mips/kernel/syscalls/syscall_n64.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n64.tbl
@@ -381,3 +381,5 @@
464 n64 getxattrat sys_getxattrat
465 n64 listxattrat sys_listxattrat
466 n64 removexattrat sys_removexattrat
+467 n64 getfsxattrat sys_getfsxattrat
+468 n64 setfsxattrat sys_setfsxattrat
diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl
index 349b8aad1159f404103bd2057a1e64e9bf309f18..6c00436807c57c492ba957fcd59af1202231cf80 100644
--- a/arch/mips/kernel/syscalls/syscall_o32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_o32.tbl
@@ -454,3 +454,5 @@
464 o32 getxattrat sys_getxattrat
465 o32 listxattrat sys_listxattrat
466 o32 removexattrat sys_removexattrat
+467 o32 getfsxattrat sys_getfsxattrat
+468 o32 setfsxattrat sys_setfsxattrat
diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
index d9fc94c869657fcfbd7aca1d5f5abc9fae2fb9d8..b3578fac43d6b65167787fcc97d2d09f5a9828e7 100644
--- a/arch/parisc/kernel/syscalls/syscall.tbl
+++ b/arch/parisc/kernel/syscalls/syscall.tbl
@@ -465,3 +465,5 @@
464 common getxattrat sys_getxattrat
465 common listxattrat sys_listxattrat
466 common removexattrat sys_removexattrat
+467 common getfsxattrat sys_getfsxattrat
+468 common setfsxattrat sys_setfsxattrat
diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
index d8b4ab78bef076bd50d49b87dea5060fd8c1686a..808045d82c9465c3bfa96b15947546efe5851e9a 100644
--- a/arch/powerpc/kernel/syscalls/syscall.tbl
+++ b/arch/powerpc/kernel/syscalls/syscall.tbl
@@ -557,3 +557,5 @@
464 common getxattrat sys_getxattrat
465 common listxattrat sys_listxattrat
466 common removexattrat sys_removexattrat
+467 common getfsxattrat sys_getfsxattrat
+468 common setfsxattrat sys_setfsxattrat
diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
index e9115b4d8b635b846e5c9ad6ce229605323723a5..78dfc2c184d4815baf8a9e61c546c9936d58a47c 100644
--- a/arch/s390/kernel/syscalls/syscall.tbl
+++ b/arch/s390/kernel/syscalls/syscall.tbl
@@ -469,3 +469,5 @@
464 common getxattrat sys_getxattrat sys_getxattrat
465 common listxattrat sys_listxattrat sys_listxattrat
466 common removexattrat sys_removexattrat sys_removexattrat
+467 common getfsxattrat sys_getfsxattrat sys_getfsxattrat
+468 common setfsxattrat sys_setfsxattrat sys_setfsxattrat
diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
index c8cad33bf250ea110de37bd1407f5a43ec5e38f2..d5a5c8339f0ed25ea07c4aba90351d352033c8a0 100644
--- a/arch/sh/kernel/syscalls/syscall.tbl
+++ b/arch/sh/kernel/syscalls/syscall.tbl
@@ -470,3 +470,5 @@
464 common getxattrat sys_getxattrat
465 common listxattrat sys_listxattrat
466 common removexattrat sys_removexattrat
+467 common getfsxattrat sys_getfsxattrat
+468 common setfsxattrat sys_setfsxattrat
diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
index 727f99d333b304b3db0711953a3d91ece18a28eb..817dcd8603bcbffc47f3f59aa3b74b16486453d0 100644
--- a/arch/sparc/kernel/syscalls/syscall.tbl
+++ b/arch/sparc/kernel/syscalls/syscall.tbl
@@ -512,3 +512,5 @@
464 common getxattrat sys_getxattrat
465 common listxattrat sys_listxattrat
466 common removexattrat sys_removexattrat
+467 common getfsxattrat sys_getfsxattrat
+468 common setfsxattrat sys_setfsxattrat
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 4d0fb2fba7e208ae9455459afe11e277321d9f74..b4842c027c5d00c0236b2ba89387c5e2267447bd 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -472,3 +472,5 @@
464 i386 getxattrat sys_getxattrat
465 i386 listxattrat sys_listxattrat
466 i386 removexattrat sys_removexattrat
+467 i386 getfsxattrat sys_getfsxattrat
+468 i386 setfsxattrat sys_setfsxattrat
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 5eb708bff1c791debd6cfc5322583b2ae53f6437..b6f0a7236aaee624cf9b484239a1068085a8ffe1 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -390,6 +390,8 @@
464 common getxattrat sys_getxattrat
465 common listxattrat sys_listxattrat
466 common removexattrat sys_removexattrat
+467 common getfsxattrat sys_getfsxattrat
+468 common setfsxattrat sys_setfsxattrat

#
# 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 37effc1b134eea061f2c350c1d68b4436b65a4dd..425d56be337d1de22f205ac503df61ff86224fee 100644
--- a/arch/xtensa/kernel/syscalls/syscall.tbl
+++ b/arch/xtensa/kernel/syscalls/syscall.tbl
@@ -437,3 +437,5 @@
464 common getxattrat sys_getxattrat
465 common listxattrat sys_listxattrat
466 common removexattrat sys_removexattrat
+467 common getfsxattrat sys_getfsxattrat
+468 common setfsxattrat sys_setfsxattrat
diff --git a/fs/inode.c b/fs/inode.c
index 6b4c77268fc0ecace4ac78a9ca777fbffc277f4a..b2dddd9db4fabaf67a6cbf541a86978b290411ec 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -23,6 +23,9 @@
#include <linux/rw_hint.h>
#include <linux/seq_file.h>
#include <linux/debugfs.h>
+#include <linux/syscalls.h>
+#include <linux/fileattr.h>
+#include <linux/namei.h>
#include <trace/events/writeback.h>
#define CREATE_TRACE_POINTS
#include <trace/events/timestamp.h>
@@ -2953,3 +2956,75 @@ umode_t mode_strip_sgid(struct mnt_idmap *idmap,
return mode & ~S_ISGID;
}
EXPORT_SYMBOL(mode_strip_sgid);
+
+SYSCALL_DEFINE4(getfsxattrat, int, dfd, const char __user *, filename,
+ struct fsxattr __user *, fsx, unsigned int, at_flags)
+{
+ CLASS(fd, dir)(dfd);
+ struct fileattr fa;
+ struct path filepath;
+ int error;
+ unsigned int lookup_flags = 0;
+
+ if ((at_flags & ~(AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH)) != 0)
+ return -EINVAL;
+
+ if (at_flags & AT_SYMLINK_FOLLOW)
+ lookup_flags |= LOOKUP_FOLLOW;
+
+ if (at_flags & AT_EMPTY_PATH)
+ lookup_flags |= LOOKUP_EMPTY;
+
+ if (fd_empty(dir))
+ return -EBADF;
+
+ error = user_path_at(dfd, filename, lookup_flags, &filepath);
+ if (error)
+ return error;
+
+ error = vfs_fileattr_get(filepath.dentry, &fa);
+ if (!error)
+ error = copy_fsxattr_to_user(&fa, fsx);
+
+ path_put(&filepath);
+ return error;
+}
+
+SYSCALL_DEFINE4(setfsxattrat, int, dfd, const char __user *, filename,
+ struct fsxattr __user *, fsx, unsigned int, at_flags)
+{
+ CLASS(fd, dir)(dfd);
+ struct fileattr fa;
+ struct path filepath;
+ int error;
+ unsigned int lookup_flags = 0;
+
+ if ((at_flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
+ return -EINVAL;
+
+ if (at_flags & AT_SYMLINK_FOLLOW)
+ lookup_flags |= LOOKUP_FOLLOW;
+
+ if (at_flags & AT_EMPTY_PATH)
+ lookup_flags |= LOOKUP_EMPTY;
+
+ if (fd_empty(dir))
+ return -EBADF;
+
+ if (copy_fsxattr_from_user(&fa, fsx))
+ return -EFAULT;
+
+ error = user_path_at(dfd, filename, lookup_flags, &filepath);
+ if (error)
+ return error;
+
+ error = mnt_want_write(filepath.mnt);
+ if (!error) {
+ error = vfs_fileattr_set(file_mnt_idmap(fd_file(dir)),
+ filepath.dentry, &fa);
+ mnt_drop_write(filepath.mnt);
+ }
+
+ path_put(&filepath);
+ return error;
+}
diff --git a/fs/ioctl.c b/fs/ioctl.c
index 638a36be31c14afc66a7fd6eb237d9545e8ad997..dc160c2ef145e4931d625f1f93c2a8ae7f87abf3 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -558,8 +558,7 @@ int copy_fsxattr_to_user(const struct fileattr *fa, struct fsxattr __user *ufa)
}
EXPORT_SYMBOL(copy_fsxattr_to_user);

-static int copy_fsxattr_from_user(struct fileattr *fa,
- struct fsxattr __user *ufa)
+int copy_fsxattr_from_user(struct fileattr *fa, struct fsxattr __user *ufa)
{
struct fsxattr xfa;

@@ -646,6 +645,19 @@ static int fileattr_set_prepare(struct inode *inode,
if (fa->fsx_cowextsize == 0)
fa->fsx_xflags &= ~FS_XFLAG_COWEXTSIZE;

+ /*
+ * The only use case for special files is to set project ID, forbid any
+ * other attributes
+ */
+ if (!(S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode))) {
+ if (fa->fsx_xflags & ~FS_XFLAG_PROJINHERIT)
+ return -EINVAL;
+ if (!S_ISLNK(inode->i_mode) && fa->fsx_nextents)
+ return -EINVAL;
+ if (fa->fsx_extsize || fa->fsx_cowextsize)
+ return -EINVAL;
+ }
+
return 0;
}

diff --git a/include/linux/fileattr.h b/include/linux/fileattr.h
index 47c05a9851d0600964b644c9c7218faacfd865f8..8598e94b530b8b280a2697eaf918dd60f573d6ee 100644
--- a/include/linux/fileattr.h
+++ b/include/linux/fileattr.h
@@ -34,6 +34,7 @@ struct fileattr {
};

int copy_fsxattr_to_user(const struct fileattr *fa, struct fsxattr __user *ufa);
+int copy_fsxattr_from_user(struct fileattr *fa, struct fsxattr __user *ufa);

void fileattr_fill_xflags(struct fileattr *fa, u32 xflags);
void fileattr_fill_flags(struct fileattr *fa, u32 flags);
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index c6333204d45130eb022f6db460eea34a1f6e91db..3134d463d9af64c6e78adb37bff4b91f77b5305f 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -371,6 +371,10 @@ 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_getfsxattrat(int dfd, const char __user *filename,
+ struct fsxattr *fsx, unsigned int at_flags);
+asmlinkage long sys_setfsxattrat(int dfd, const char __user *filename,
+ struct fsxattr *fsx, 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 88dc393c2bca38c0fa1b3fae579f7cfe4931223c..50be2e1007bc2779120d05c6e9512a689f86779c 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -850,8 +850,14 @@ __SYSCALL(__NR_listxattrat, sys_listxattrat)
#define __NR_removexattrat 466
__SYSCALL(__NR_removexattrat, sys_removexattrat)

+/* fs/inode.c */
+#define __NR_getfsxattrat 467
+__SYSCALL(__NR_getfsxattrat, sys_getfsxattrat)
+#define __NR_setfsxattrat 468
+__SYSCALL(__NR_setfsxattrat, sys_setfsxattrat)
+
#undef __NR_syscalls
-#define __NR_syscalls 467
+#define __NR_syscalls 469

/*
* 32 bit systems traditionally used different

---
base-commit: ffd294d346d185b70e28b1a28abe367bbfe53c04
change-id: 20250114-xattrat-syscall-6a1136d2db59

Best regards,
--
Andrey Albershteyn <aalbersh@kernel.org>