Merge tag 'v6.6-vfs.fchmodat2' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull fchmodat2 system call from Christian Brauner:
 "This adds the fchmodat2() system call. It is a revised version of the
  fchmodat() system call, adding a missing flag argument. Support for
  both AT_SYMLINK_NOFOLLOW and AT_EMPTY_PATH are included.

  Adding this system call revision has been a longstanding request but
  so far has always fallen through the cracks. While the kernel
  implementation of fchmodat() does not have a flag argument the libc
  provided POSIX-compliant fchmodat(3) version does. Both glibc and musl
  have to implement a workaround in order to support AT_SYMLINK_NOFOLLOW
  (see [1] and [2]).

  The workaround is brittle because it relies not just on O_PATH and
  O_NOFOLLOW semantics and procfs magic links but also on our rather
  inconsistent symlink semantics.

  This gives userspace a proper fchmodat2() system call that libcs can
  use to properly implement fchmodat(3) and allows them to get rid of
  their hacks. In this case it will immediately benefit them as the
  current workaround is already defunct because of aformentioned
  inconsistencies.

  In addition to AT_SYMLINK_NOFOLLOW, give userspace the ability to use
  AT_EMPTY_PATH with fchmodat2(). This is already possible with
  fchownat() so there's no reason to not also support it for
  fchmodat2().

  The implementation is simple and comes with selftests. Implementation
  of the system call and wiring up the system call are done as separate
  patches even though they could arguably be one patch. But in case
  there are merge conflicts from other system call additions it can be
  beneficial to have separate patches"

Link: https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/fchmodat.c;h=17eca54051ee28ba1ec3f9aed170a62630959143;hb=a492b1e5ef7ab50c6fdd4e4e9879ea5569ab0a6c#l35 [1]
Link: https://git.musl-libc.org/cgit/musl/tree/src/stat/fchmodat.c?id=718f363bc2067b6487900eddc9180c84e7739f80#n28 [2]

* tag 'v6.6-vfs.fchmodat2' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  selftests: fchmodat2: remove duplicate unneeded defines
  fchmodat2: add support for AT_EMPTY_PATH
  selftests: Add fchmodat2 selftest
  arch: Register fchmodat2, usually as syscall 452
  fs: Add fchmodat2()
  Non-functional cleanup of a "__user * filename"

2 files changed, 7 insertions, 2 deletions

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 03e3d0121d5e..5690aef7b3a8 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -438,8 +438,10 @@ asmlinkage long sys_chdir(const char __user *filename);
 asmlinkage long sys_fchdir(unsigned int fd);
 asmlinkage long sys_chroot(const char __user *filename);
 asmlinkage long sys_fchmod(unsigned int fd, umode_t mode);
-asmlinkage long sys_fchmodat(int dfd, const char __user * filename,
+asmlinkage long sys_fchmodat(int dfd, const char __user *filename,
 			     umode_t mode);
+asmlinkage long sys_fchmodat2(int dfd, const char __user *filename,
+			     umode_t mode, unsigned int flags);
 asmlinkage long sys_fchownat(int dfd, const char __user *filename, uid_t user,
 			     gid_t group, int flag);
 asmlinkage long sys_fchown(unsigned int fd, uid_t user, gid_t group);
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index fd6c1cb585db..abe087c53b4b 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -820,8 +820,11 @@ __SYSCALL(__NR_set_mempolicy_home_node, sys_set_mempolicy_home_node)
 #define __NR_cachestat 451
 __SYSCALL(__NR_cachestat, sys_cachestat)
 
+#define __NR_fchmodat2 452
+__SYSCALL(__NR_fchmodat2, sys_fchmodat2)
+
 #undef __NR_syscalls
-#define __NR_syscalls 452
+#define __NR_syscalls 453
 
 /*
  * 32 bit systems traditionally used different