On Tue, 28 Feb 2017 12:23:01 -0600 Eric Blake <eblake@xxxxxxxxxx> wrote: > On 02/28/2017 11:03 AM, Greg Kurz 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 <groug@xxxxxxxx> > > --- > > Might also be worth mentioning that this patch is required in order to > solve CVE-2016-9602, per discussion at > https://lists.gnu.org/archive/html/qemu-devel/2017-02/msg06089.html > True. I'll add a reference to it if I have to send a v2. > > +++ 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); > > Is the indentation off here? > This is linux style indent with tabs+spaces. FWIW it is displayed correctly in vi and emacs (I've simply copied the sys_fchmodat() declaration). > Reviewed-by: Eric Blake <eblake@xxxxxxxxxx> > >
Attachment:
pgpWLjSfrKXYo.pgp
Description: OpenPGP digital signature
