2014-01-21 07:30:30

by Florian Weimer

Subject: Re: [PATCH 1/2] vfs: Add fchmodat4 syscall: fchmodat with flag argument

On 01/13/2012 02:53 AM, Andrew Ayer wrote:
> This adds a 4 argument version of fchmodat (fchmodat4) that
> supports a flag argument, as specified by POSIX. It supports
> the same two flags as fchownat: AT_SYMLINK_NOFOLLOW and AT_EMPTY_PATH.

I don't think it's possible to emulate AT_EMPTY_PATH in user space, so I
wonder if this could be applied, and if not, why. Thanks.

--
Florian Weimer / Red Hat Product Security Team

2014-01-21 19:06:35

by Andrew Ayer

Subject: Re: [PATCH 1/2] vfs: Add fchmodat4 syscall: fchmodat with flag argument

On Tue, 21 Jan 2014 08:30:16 +0100
Florian Weimer <[email protected]> wrote:

> On 01/13/2012 02:53 AM, Andrew Ayer wrote:
> > This adds a 4 argument version of fchmodat (fchmodat4) that
> > supports a flag argument, as specified by POSIX. It supports
> > the same two flags as fchownat: AT_SYMLINK_NOFOLLOW and AT_EMPTY_PATH.
>
> I don't think it's possible to emulate AT_EMPTY_PATH in user space, so I
> wonder if this could be applied, and if not, why. Thanks.

The original patch no longer applies because there were some
minor changes to fs/open.c. I'll fix up the patch and send it in.

I too would very much like to see this applied, or to know why it can't
be.

Thanks,
Andrew

2014-01-21 19:06:32

by Andrew Ayer

Subject: [PATCH] vfs: Add version of fchmodat with flag argument

This adds a 4 argument version of fchmodat (fchmodat4) that
supports a flag argument, as specified by POSIX. It supports
the same two flags as fchownat: AT_SYMLINK_NOFOLLOW and AT_EMPTY_PATH.

Signed-off-by: Andrew Ayer <[email protected]>
---
fs/open.c | 23 ++++++++++++++++++++---
include/linux/syscalls.h | 2 ++
2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/fs/open.c b/fs/open.c
index 4b3e1ed..6f661f9 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -469,6 +469,9 @@ static int chmod_common(struct path *path, umode_t mode)
struct iattr newattrs;
int error;

+ if (S_ISLNK(inode->i_mode))
+ return -EOPNOTSUPP;
+
error = mnt_want_write(path->mnt);
if (error)
return error;
@@ -506,9 +509,22 @@ SYSCALL_DEFINE2(fchmod, unsigned int, fd, umode_t, mode)

SYSCALL_DEFINE3(fchmodat, int, dfd, const char __user *, filename, umode_t, mode)
{
+ return sys_fchmodat4(dfd, filename, mode, 0);
+}
+
+SYSCALL_DEFINE4(fchmodat4, 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 | AT_EMPTY_PATH)) != 0)
+ goto out;
+
+ lookup_flags = (flag & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW;
+ if (flag & AT_EMPTY_PATH)
+ lookup_flags |= LOOKUP_EMPTY;
retry:
error = user_path_at(dfd, filename, lookup_flags, &path);
if (!error) {
@@ -519,12 +535,13 @@ retry:
goto retry;
}
}
+out:
return error;
}

SYSCALL_DEFINE2(chmod, const char __user *, filename, umode_t, mode)
{
- return sys_fchmodat(AT_FDCWD, filename, mode);
+ return sys_fchmodat4(AT_FDCWD, filename, mode, 0);
}

static int chown_common(struct path *path, uid_t user, gid_t group)
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 40ed9e9..32811df 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -747,6 +747,8 @@ 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_fchmodat4(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,
--
1.7.10.4