Re: [PATCH v4 3/3] fs: introduce getfsxattrat and setfsxattrat syscalls
From: Christian Brauner <brauner@kernel.org>
Date: 2025-04-22 14:59:17
Also in:
linux-alpha, linux-arch, linux-fsdevel, linux-m68k, linux-mips, linux-s390, linux-security-module, linux-sh, linux-xfs, linuxppc-dev, lkml, sparclinux
On Fri, Mar 21, 2025 at 08:48:42PM +0100, Andrey Albershteyn wrote:
quoted hunk ↗ jump to hunk
From: Andrey Albershteyn <redacted> 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. CC: linux-api@vger.kernel.org CC: linux-fsdevel@vger.kernel.org CC: linux-xfs@vger.kernel.org Signed-off-by: Andrey Albershteyn <redacted> 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/inode.c | 130 ++++++++++++++++++++++++++++ include/linux/syscalls.h | 6 ++ include/uapi/asm-generic/unistd.h | 8 +- include/uapi/linux/fs.h | 3 + 20 files changed, 178 insertions(+), 1 deletion(-)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_setfsxattratdiff --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_setfsxattratdiff --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_setfsxattratdiff --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_setfsxattratdiff --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_setfsxattratdiff --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_setfsxattratdiff --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_setfsxattratdiff --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_setfsxattratdiff --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_setfsxattratdiff --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_setfsxattratdiff --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_setfsxattratdiff --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_setfsxattratdiff --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_setfsxattratdiff --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_setfsxattratdiff --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 differentlydiff --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_setfsxattratdiff --git a/fs/inode.c b/fs/inode.c index 6b4c77268fc0ecace4ac78a9ca777fbffc277f4a..811debf379ab299f287ed90863277cfda27db30c 100644 --- a/fs/inode.c +++ b/fs/inode.c
I really dislike the name fsxattr for a lot of reasons but it definitely shouldn't go in inode.c. Just add a new fs/file_attr.c file and move all the relevant helpers from fs/ioctl.c in there and then add the system calls. Otherwise it's just all very confusing.
quoted hunk ↗ jump to hunk
@@ -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 +2956,130 @@ umode_t mode_strip_sgid(struct mnt_idmap *idmap, return mode & ~S_ISGID; } EXPORT_SYMBOL(mode_strip_sgid); + +SYSCALL_DEFINE5(getfsxattrat, int, dfd, const char __user *, filename,
This is really misnamed. It will end up confusing userspace to no end: getxattr() getxattrat() getfsxattrat() Please name this file_setattr() and file_getattr(). There's also no need for the *at() prefix. We've never been consistent with that. We have plent of system calls that to fd+path without having an *at() prefix. And here it's especially unneeded because there's no pre-existing system calls that would even force the use of that prefix.
+ struct fsxattr __user *, ufsx, size_t, usize,
+ unsigned int, at_flags)
+{
+ struct fileattr fa = {};
+ struct path filepath;
+ int error;
+ unsigned int lookup_flags = 0;
+ struct filename *name;
+ struct fsxattr fsx = {};
+
+ BUILD_BUG_ON(sizeof(struct fsxattr) < FSXATTR_SIZE_VER0);
+ BUILD_BUG_ON(sizeof(struct fsxattr) != FSXATTR_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 (at_flags & AT_EMPTY_PATH)
+ lookup_flags |= LOOKUP_EMPTY;
+
+ if (usize > PAGE_SIZE)
+ return -E2BIG;
+
+ if (usize < FSXATTR_SIZE_VER0)
+ return -EINVAL;
+
+ name = getname_maybe_null(filename, at_flags);
+ if (!name) {
This is broken as it doesn't handle AT_FDCWD correctly. You need:
name = getname_maybe_null(filename, at_flags);
if (IS_ERR(name))
return PTR_ERR(name);
if (!name && dfd >= 0) {
CLASS(fd, f)(dfd);
+ CLASS(fd, f)(dfd); + + if (fd_empty(f)) + return -EBADF;
I'm pretty sure you can just do a:
path = fd_file(f_to)->f_path;
path_get(&path);
and then the vfs_fileattr_get() call and the path_put() call can be
shared between the two branches. Note that you can also use:
struct path path __free(path_put) = NULL;
and then the cleanup infrastructure will handle the path_put() for you.
+ error = vfs_fileattr_get(file_dentry(fd_file(f)), &fa);
+ } else {
+ error = filename_lookup(dfd, name, lookup_flags, &filepath,
+ NULL);
+ if (error)
+ goto out;
+ error = vfs_fileattr_get(filepath.dentry, &fa);
+ path_put(&filepath);
+ }
+ if (error == -ENOIOCTLCMD)
+ error = -EOPNOTSUPP;
+ if (!error) {
+ fileattr_to_fsxattr(&fa, &fsx);
+ error = copy_struct_to_user(ufsx, usize, &fsx,
+ sizeof(struct fsxattr), NULL);
+ }
+out:
+ putname(name);
+ return error;
+}
+
+SYSCALL_DEFINE5(setfsxattrat, int, dfd, const char __user *, filename,
+ struct fsxattr __user *, ufsx, size_t, usize,
+ unsigned int, at_flags)
+{
+ struct fileattr fa;
+ struct path filepath;
+ int error;
+ unsigned int lookup_flags = 0;
+ struct filename *name;
+ struct mnt_idmap *idmap;
+ struct dentry *dentry;
+ struct vfsmount *mnt;
+ struct fsxattr fsx = {};
+
+ BUILD_BUG_ON(sizeof(struct fsxattr) < FSXATTR_SIZE_VER0);
+ BUILD_BUG_ON(sizeof(struct fsxattr) != FSXATTR_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 (at_flags & AT_EMPTY_PATH)
+ lookup_flags |= LOOKUP_EMPTY;
+
+ if (usize > PAGE_SIZE)
+ return -E2BIG;
+
+ if (usize < FSXATTR_SIZE_VER0)
+ return -EINVAL;
+
+ error = copy_struct_from_user(&fsx, sizeof(struct fsxattr), ufsx, usize);
+ if (error)
+ return error;
+
+ fsxattr_to_fileattr(&fsx, &fa);
+
+ name = getname_maybe_null(filename, at_flags);
+ if (!name) {Same comment as above.
+ CLASS(fd, f)(dfd); + + if (fd_empty(f)) + return -EBADF; + + idmap = file_mnt_idmap(fd_file(f)); + dentry = file_dentry(fd_file(f)); + mnt = fd_file(f)->f_path.mnt;
This is a UAF. fd_file(f)->f_path.mnt and file_dentry(fd_file(f)) will get auto cleaned at the end of the scope. By the time you call vfs_fileattr_set() nothing pins them anymore... In general, same comment about unifying the branches as for the get case via path_get() as above. And just keep the path around don't store mount and dentry separately.
quoted hunk ↗ jump to hunk
+ } else { + error = filename_lookup(dfd, name, lookup_flags, &filepath, + NULL); + if (error) + return error; + + idmap = mnt_idmap(filepath.mnt); + dentry = filepath.dentry; + mnt = filepath.mnt; + } + + error = mnt_want_write(mnt); + if (!error) { + error = vfs_fileattr_set(idmap, dentry, &fa); + if (error == -ENOIOCTLCMD) + error = -EOPNOTSUPP; + mnt_drop_write(mnt); + } + + path_put(&filepath); + return error; +}diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index c6333204d45130eb022f6db460eea34a1f6e91db..e242ea39b3e63a8008bc777764b616fd63bd40c4 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_getfsxattrat(int dfd, const char __user *filename, + struct fsxattr __user *ufsx, size_t usize, + unsigned int at_flags); +asmlinkage long sys_setfsxattrat(int dfd, const char __user *filename, + struct fsxattr __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 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 differentdiff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h index 7539717707337a8cb22396a869baba3bafa08371..aed753e5d50c97da9b895a187fdaecf0477db74b 100644 --- a/include/uapi/linux/fs.h +++ b/include/uapi/linux/fs.h@@ -139,6 +139,9 @@ struct fsxattr { unsigned char fsx_pad[8]; }; +#define FSXATTR_SIZE_VER0 28 +#define FSXATTR_SIZE_LATEST FSXATTR_SIZE_VER0 + /* * Flags for the fsx_xflags field */-- 2.47.2