[CC += [email protected]]
Hello Greg,
Since this is a kernel-user-space API change, please CC linux-api@.
The kernel source file Documentation/SubmitChecklist notes that all
Linux kernel patches that change userspace interfaces should be CCed
to [email protected], so that the various parties who are
interested in API changes are informed. For further information, see
https://www.kernel.org/doc/man-pages/linux-api-ml.html
Thanks,
Michael
On Tue, Feb 28, 2017 at 6:03 PM, Greg Kurz <[email protected]> wrote:
> According to the POSIX.1-2008 manual page [1], the fchmodat() function has
> a flag argument which may be passed the following value:
>
> AT_SYMLINK_NOFOLLOW
> If path names a symbolic link, then the mode of the symbolic link is
> changed.
>
> and the following error may be returned:
>
> [EOPNOTSUPP]
> The AT_SYMLINK_NOFOLLOW bit is set in the flag argument, path names a
> symbolic link, and the system does not support changing the mode of a
> symbolic link.
>
> The linux kernel doesn't support changing the mode of a symbolic link, but
> the current implementation doesn't even have a flag argument. It is then
> up to userspace to deal with that. Unfortunately, it is impossible to
> implement the POSIX behavior in a race-free manner.
>
> This patch introduces a new fchmodat2() syscall with a flag argument to
> address the issue.
>
> [1] http://pubs.opengroup.org/onlinepubs/9699919799/functions/chmod.html
>
> Signed-off-by: Greg Kurz <[email protected]>
> ---
> fs/open.c | 23 +++++++++++++++++++----
> include/linux/syscalls.h | 2 ++
> include/uapi/asm-generic/unistd.h | 4 +++-
> scripts/checksyscalls.sh | 3 ++-
> 4 files changed, 26 insertions(+), 6 deletions(-)
>
> diff --git a/fs/open.c b/fs/open.c
> index 9921f70bc5ca..66a8c19f72ca 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -558,24 +558,39 @@ SYSCALL_DEFINE2(fchmod, unsigned int, fd, umode_t, mode)
> return err;
> }
>
> -SYSCALL_DEFINE3(fchmodat, int, dfd, const char __user *, filename, umode_t, mode)
> +SYSCALL_DEFINE4(fchmodat2, int, dfd, const char __user *, filename, umode_t,
> + mode, int, flag)
> {
> struct path path;
> - int error;
> - unsigned int lookup_flags = LOOKUP_FOLLOW;
> + int error = -EINVAL;
> + unsigned int lookup_flags;
> +
> + if ((flag & ~AT_SYMLINK_NOFOLLOW) != 0)
> + goto out;
> +
> + lookup_flags = (flag & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW;
> retry:
> error = user_path_at(dfd, filename, lookup_flags, &path);
> if (!error) {
> - error = chmod_common(&path, mode);
> + error = -EOPNOTSUPP;
> + if (!d_is_symlink(path.dentry))
> + error = chmod_common(&path, mode);
> path_put(&path);
> if (retry_estale(error, lookup_flags)) {
> lookup_flags |= LOOKUP_REVAL;
> goto retry;
> }
> }
> +out:
> return error;
> }
>
> +SYSCALL_DEFINE3(fchmodat, int, dfd, const char __user *, filename, umode_t,
> + mode)
> +{
> + return sys_fchmodat2(dfd, filename, mode, 0);
> +}
> +
> SYSCALL_DEFINE2(chmod, const char __user *, filename, umode_t, mode)
> {
> return sys_fchmodat(AT_FDCWD, filename, mode);
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index 91a740f6b884..982089d55b31 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -775,6 +775,8 @@ asmlinkage long sys_futimesat(int dfd, const char __user *filename,
> asmlinkage long sys_faccessat(int dfd, const char __user *filename, int mode);
> 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, int flag);
> asmlinkage long sys_fchownat(int dfd, const char __user *filename, uid_t user,
> gid_t group, int flag);
> asmlinkage long sys_openat(int dfd, const char __user *filename, int flags,
> diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
> index 9b1462e38b82..e8b0a00908b1 100644
> --- a/include/uapi/asm-generic/unistd.h
> +++ b/include/uapi/asm-generic/unistd.h
> @@ -730,9 +730,11 @@ __SYSCALL(__NR_pkey_mprotect, sys_pkey_mprotect)
> __SYSCALL(__NR_pkey_alloc, sys_pkey_alloc)
> #define __NR_pkey_free 290
> __SYSCALL(__NR_pkey_free, sys_pkey_free)
> +#define __NR_fchmodat2 291
> +__SYSCALL(__NR_fchmodat2, sys_fchmodat2)
>
> #undef __NR_syscalls
> -#define __NR_syscalls 291
> +#define __NR_syscalls 292
>
> /*
> * All syscalls below here should go away really,
> diff --git a/scripts/checksyscalls.sh b/scripts/checksyscalls.sh
> index 2c9082ba6137..2e7471a1d308 100755
> --- a/scripts/checksyscalls.sh
> +++ b/scripts/checksyscalls.sh
> @@ -19,7 +19,7 @@ cat << EOF
> #define __IGNORE_link /* linkat */
> #define __IGNORE_unlink /* unlinkat */
> #define __IGNORE_mknod /* mknodat */
> -#define __IGNORE_chmod /* fchmodat */
> +#define __IGNORE_chmod /* fchmodat2 */
> #define __IGNORE_chown /* fchownat */
> #define __IGNORE_mkdir /* mkdirat */
> #define __IGNORE_rmdir /* unlinkat */
> @@ -39,6 +39,7 @@ cat << EOF
>
> /* Missing flags argument */
> #define __IGNORE_renameat /* renameat2 */
> +#define __IGNORE_fchmodat /* fchmodat2 */
>
> /* CLOEXEC flag */
> #define __IGNORE_pipe /* pipe2 */
>
--
Michael Kerrisk Linux man-pages maintainer;
http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface", http://blog.man7.org/
On Wed, 1 Mar 2017 10:01:53 +0100
Michael Kerrisk <[email protected]> wrote:
> [CC += [email protected]]
>
> Hello Greg,
>
> Since this is a kernel-user-space API change, please CC linux-api@.
> The kernel source file Documentation/SubmitChecklist notes that all
> Linux kernel patches that change userspace interfaces should be CCed
> to [email protected], so that the various parties who are
> interested in API changes are informed. For further information, see
> https://www.kernel.org/doc/man-pages/linux-api-ml.html
>
> Thanks,
>
> Michael
>
My bad :-\
Anyway, since I had no feedback so far, I'll send a v2 and this time I'll
rembember to Cc [email protected].
Thanks,
--
Greg
>
> On Tue, Feb 28, 2017 at 6:03 PM, Greg Kurz <[email protected]> wrote:
> > According to the POSIX.1-2008 manual page [1], the fchmodat() function has
> > a flag argument which may be passed the following value:
> >
> > AT_SYMLINK_NOFOLLOW
> > If path names a symbolic link, then the mode of the symbolic link is
> > changed.
> >
> > and the following error may be returned:
> >
> > [EOPNOTSUPP]
> > The AT_SYMLINK_NOFOLLOW bit is set in the flag argument, path names a
> > symbolic link, and the system does not support changing the mode of a
> > symbolic link.
> >
> > The linux kernel doesn't support changing the mode of a symbolic link, but
> > the current implementation doesn't even have a flag argument. It is then
> > up to userspace to deal with that. Unfortunately, it is impossible to
> > implement the POSIX behavior in a race-free manner.
> >
> > This patch introduces a new fchmodat2() syscall with a flag argument to
> > address the issue.
> >
> > [1] http://pubs.opengroup.org/onlinepubs/9699919799/functions/chmod.html
> >
> > Signed-off-by: Greg Kurz <[email protected]>
> > ---
> > fs/open.c | 23 +++++++++++++++++++----
> > include/linux/syscalls.h | 2 ++
> > include/uapi/asm-generic/unistd.h | 4 +++-
> > scripts/checksyscalls.sh | 3 ++-
> > 4 files changed, 26 insertions(+), 6 deletions(-)
> >
> > diff --git a/fs/open.c b/fs/open.c
> > index 9921f70bc5ca..66a8c19f72ca 100644
> > --- a/fs/open.c
> > +++ b/fs/open.c
> > @@ -558,24 +558,39 @@ SYSCALL_DEFINE2(fchmod, unsigned int, fd, umode_t, mode)
> > return err;
> > }
> >
> > -SYSCALL_DEFINE3(fchmodat, int, dfd, const char __user *, filename, umode_t, mode)
> > +SYSCALL_DEFINE4(fchmodat2, int, dfd, const char __user *, filename, umode_t,
> > + mode, int, flag)
> > {
> > struct path path;
> > - int error;
> > - unsigned int lookup_flags = LOOKUP_FOLLOW;
> > + int error = -EINVAL;
> > + unsigned int lookup_flags;
> > +
> > + if ((flag & ~AT_SYMLINK_NOFOLLOW) != 0)
> > + goto out;
> > +
> > + lookup_flags = (flag & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW;
> > retry:
> > error = user_path_at(dfd, filename, lookup_flags, &path);
> > if (!error) {
> > - error = chmod_common(&path, mode);
> > + error = -EOPNOTSUPP;
> > + if (!d_is_symlink(path.dentry))
> > + error = chmod_common(&path, mode);
> > path_put(&path);
> > if (retry_estale(error, lookup_flags)) {
> > lookup_flags |= LOOKUP_REVAL;
> > goto retry;
> > }
> > }
> > +out:
> > return error;
> > }
> >
> > +SYSCALL_DEFINE3(fchmodat, int, dfd, const char __user *, filename, umode_t,
> > + mode)
> > +{
> > + return sys_fchmodat2(dfd, filename, mode, 0);
> > +}
> > +
> > SYSCALL_DEFINE2(chmod, const char __user *, filename, umode_t, mode)
> > {
> > return sys_fchmodat(AT_FDCWD, filename, mode);
> > diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> > index 91a740f6b884..982089d55b31 100644
> > --- a/include/linux/syscalls.h
> > +++ b/include/linux/syscalls.h
> > @@ -775,6 +775,8 @@ asmlinkage long sys_futimesat(int dfd, const char __user *filename,
> > asmlinkage long sys_faccessat(int dfd, const char __user *filename, int mode);
> > 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, int flag);
> > asmlinkage long sys_fchownat(int dfd, const char __user *filename, uid_t user,
> > gid_t group, int flag);
> > asmlinkage long sys_openat(int dfd, const char __user *filename, int flags,
> > diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
> > index 9b1462e38b82..e8b0a00908b1 100644
> > --- a/include/uapi/asm-generic/unistd.h
> > +++ b/include/uapi/asm-generic/unistd.h
> > @@ -730,9 +730,11 @@ __SYSCALL(__NR_pkey_mprotect, sys_pkey_mprotect)
> > __SYSCALL(__NR_pkey_alloc, sys_pkey_alloc)
> > #define __NR_pkey_free 290
> > __SYSCALL(__NR_pkey_free, sys_pkey_free)
> > +#define __NR_fchmodat2 291
> > +__SYSCALL(__NR_fchmodat2, sys_fchmodat2)
> >
> > #undef __NR_syscalls
> > -#define __NR_syscalls 291
> > +#define __NR_syscalls 292
> >
> > /*
> > * All syscalls below here should go away really,
> > diff --git a/scripts/checksyscalls.sh b/scripts/checksyscalls.sh
> > index 2c9082ba6137..2e7471a1d308 100755
> > --- a/scripts/checksyscalls.sh
> > +++ b/scripts/checksyscalls.sh
> > @@ -19,7 +19,7 @@ cat << EOF
> > #define __IGNORE_link /* linkat */
> > #define __IGNORE_unlink /* unlinkat */
> > #define __IGNORE_mknod /* mknodat */
> > -#define __IGNORE_chmod /* fchmodat */
> > +#define __IGNORE_chmod /* fchmodat2 */
> > #define __IGNORE_chown /* fchownat */
> > #define __IGNORE_mkdir /* mkdirat */
> > #define __IGNORE_rmdir /* unlinkat */
> > @@ -39,6 +39,7 @@ cat << EOF
> >
> > /* Missing flags argument */
> > #define __IGNORE_renameat /* renameat2 */
> > +#define __IGNORE_fchmodat /* fchmodat2 */
> >
> > /* CLOEXEC flag */
> > #define __IGNORE_pipe /* pipe2 */
> >
>
>
>
On Tue, 11 Apr 2017 13:39:37 +0200
Greg Kurz <[email protected]> wrote:
> On Wed, 1 Mar 2017 10:01:53 +0100
> Michael Kerrisk <[email protected]> wrote:
>
> > [CC += [email protected]]
> >
> > Hello Greg,
> >
> > Since this is a kernel-user-space API change, please CC linux-api@.
> > The kernel source file Documentation/SubmitChecklist notes that all
> > Linux kernel patches that change userspace interfaces should be CCed
> > to [email protected], so that the various parties who are
> > interested in API changes are informed. For further information, see
> > https://www.kernel.org/doc/man-pages/linux-api-ml.html
> >
> > Thanks,
> >
> > Michael
> >
>
> My bad :-\
>
> Anyway, since I had no feedback so far, I'll send a v2 and this time I'll
> rembember to Cc [email protected].
>
> Thanks,
>
BTW, commit "186128f75392 docs-rst: add documents to development-process" moved
Documentation/SubmitChecklist to Documentation/process/submit-checklist.rst, but
the http://www.kernel.org page hasn't been updated to reflect that...
Cheers.
--
Greg
> --
> Greg
>
> >
> > On Tue, Feb 28, 2017 at 6:03 PM, Greg Kurz <[email protected]> wrote:
> > > According to the POSIX.1-2008 manual page [1], the fchmodat() function has
> > > a flag argument which may be passed the following value:
> > >
> > > AT_SYMLINK_NOFOLLOW
> > > If path names a symbolic link, then the mode of the symbolic link is
> > > changed.
> > >
> > > and the following error may be returned:
> > >
> > > [EOPNOTSUPP]
> > > The AT_SYMLINK_NOFOLLOW bit is set in the flag argument, path names a
> > > symbolic link, and the system does not support changing the mode of a
> > > symbolic link.
> > >
> > > The linux kernel doesn't support changing the mode of a symbolic link, but
> > > the current implementation doesn't even have a flag argument. It is then
> > > up to userspace to deal with that. Unfortunately, it is impossible to
> > > implement the POSIX behavior in a race-free manner.
> > >
> > > This patch introduces a new fchmodat2() syscall with a flag argument to
> > > address the issue.
> > >
> > > [1] http://pubs.opengroup.org/onlinepubs/9699919799/functions/chmod.html
> > >
> > > Signed-off-by: Greg Kurz <[email protected]>
> > > ---
> > > fs/open.c | 23 +++++++++++++++++++----
> > > include/linux/syscalls.h | 2 ++
> > > include/uapi/asm-generic/unistd.h | 4 +++-
> > > scripts/checksyscalls.sh | 3 ++-
> > > 4 files changed, 26 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/fs/open.c b/fs/open.c
> > > index 9921f70bc5ca..66a8c19f72ca 100644
> > > --- a/fs/open.c
> > > +++ b/fs/open.c
> > > @@ -558,24 +558,39 @@ SYSCALL_DEFINE2(fchmod, unsigned int, fd, umode_t, mode)
> > > return err;
> > > }
> > >
> > > -SYSCALL_DEFINE3(fchmodat, int, dfd, const char __user *, filename, umode_t, mode)
> > > +SYSCALL_DEFINE4(fchmodat2, int, dfd, const char __user *, filename, umode_t,
> > > + mode, int, flag)
> > > {
> > > struct path path;
> > > - int error;
> > > - unsigned int lookup_flags = LOOKUP_FOLLOW;
> > > + int error = -EINVAL;
> > > + unsigned int lookup_flags;
> > > +
> > > + if ((flag & ~AT_SYMLINK_NOFOLLOW) != 0)
> > > + goto out;
> > > +
> > > + lookup_flags = (flag & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW;
> > > retry:
> > > error = user_path_at(dfd, filename, lookup_flags, &path);
> > > if (!error) {
> > > - error = chmod_common(&path, mode);
> > > + error = -EOPNOTSUPP;
> > > + if (!d_is_symlink(path.dentry))
> > > + error = chmod_common(&path, mode);
> > > path_put(&path);
> > > if (retry_estale(error, lookup_flags)) {
> > > lookup_flags |= LOOKUP_REVAL;
> > > goto retry;
> > > }
> > > }
> > > +out:
> > > return error;
> > > }
> > >
> > > +SYSCALL_DEFINE3(fchmodat, int, dfd, const char __user *, filename, umode_t,
> > > + mode)
> > > +{
> > > + return sys_fchmodat2(dfd, filename, mode, 0);
> > > +}
> > > +
> > > SYSCALL_DEFINE2(chmod, const char __user *, filename, umode_t, mode)
> > > {
> > > return sys_fchmodat(AT_FDCWD, filename, mode);
> > > diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> > > index 91a740f6b884..982089d55b31 100644
> > > --- a/include/linux/syscalls.h
> > > +++ b/include/linux/syscalls.h
> > > @@ -775,6 +775,8 @@ asmlinkage long sys_futimesat(int dfd, const char __user *filename,
> > > asmlinkage long sys_faccessat(int dfd, const char __user *filename, int mode);
> > > 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, int flag);
> > > asmlinkage long sys_fchownat(int dfd, const char __user *filename, uid_t user,
> > > gid_t group, int flag);
> > > asmlinkage long sys_openat(int dfd, const char __user *filename, int flags,
> > > diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
> > > index 9b1462e38b82..e8b0a00908b1 100644
> > > --- a/include/uapi/asm-generic/unistd.h
> > > +++ b/include/uapi/asm-generic/unistd.h
> > > @@ -730,9 +730,11 @@ __SYSCALL(__NR_pkey_mprotect, sys_pkey_mprotect)
> > > __SYSCALL(__NR_pkey_alloc, sys_pkey_alloc)
> > > #define __NR_pkey_free 290
> > > __SYSCALL(__NR_pkey_free, sys_pkey_free)
> > > +#define __NR_fchmodat2 291
> > > +__SYSCALL(__NR_fchmodat2, sys_fchmodat2)
> > >
> > > #undef __NR_syscalls
> > > -#define __NR_syscalls 291
> > > +#define __NR_syscalls 292
> > >
> > > /*
> > > * All syscalls below here should go away really,
> > > diff --git a/scripts/checksyscalls.sh b/scripts/checksyscalls.sh
> > > index 2c9082ba6137..2e7471a1d308 100755
> > > --- a/scripts/checksyscalls.sh
> > > +++ b/scripts/checksyscalls.sh
> > > @@ -19,7 +19,7 @@ cat << EOF
> > > #define __IGNORE_link /* linkat */
> > > #define __IGNORE_unlink /* unlinkat */
> > > #define __IGNORE_mknod /* mknodat */
> > > -#define __IGNORE_chmod /* fchmodat */
> > > +#define __IGNORE_chmod /* fchmodat2 */
> > > #define __IGNORE_chown /* fchownat */
> > > #define __IGNORE_mkdir /* mkdirat */
> > > #define __IGNORE_rmdir /* unlinkat */
> > > @@ -39,6 +39,7 @@ cat << EOF
> > >
> > > /* Missing flags argument */
> > > #define __IGNORE_renameat /* renameat2 */
> > > +#define __IGNORE_fchmodat /* fchmodat2 */
> > >
> > > /* CLOEXEC flag */
> > > #define __IGNORE_pipe /* pipe2 */
> > >
> >
> >
> >
>