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

Andrey Albershteyn
2025-02-18T10:47:19Z

Got more comments below with private mail:

On 2025-02-11 18:22:47, Andrey Albershteyn 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);

vfs_fileattr_get() returns ENOIOCTLCMD, where EOPNOTSUPP is more
appropriate

> + 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)
^ can be const
> +{
> + 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);

same here with returned error

--
- Andrey