Re: [PATCH v3] fs: introduce getfsxattrat and setfsxattrat syscalls

H. Peter Anvin
2025-02-11T19:13:44Z

On February 11, 2025 9:22:47 AM PST, Andrey Albershteyn <aalbersh@redhat.com> wrote:
>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,

Could you please give a quick description of the API – even just the prototype – and, for the future, include in the cover letter?