linux.git/fs/utimes.c, branch v2.6.26

[patch for 2.6.26 4/4] vfs: utimensat(): fix write access check for futimens()

2008-06-23T12:43:52+00:00

The POSIX.1 draft spec for futimens()/utimensat() says:

        Only a process with the effective user ID equal to the
        user ID of the file, *or with write access to the file*,
        or with appropriate privileges may use futimens() or
        utimensat() with a null pointer as the times argument
        or with both tv_nsec fields set to the special value
        UTIME_NOW.

The important piece here is "with write access to the file", and
this matters for futimens(), which deals with an argument that
is a file descriptor referring to the file whose timestamps are
being updated,  The standard is saying that the "writability"
check is based on the file permissions, not the access mode with
which the file is opened.  (This behavior is consistent with the
semantics of FreeBSD's futimes().)  However, Linux is currently
doing the latter -- futimens(fd, times) is a library
function implemented as

       utimensat(fd, NULL, times, 0)

and within the utimensat() implementation we have the code:

                f = fget(dfd);  // dfd is 'fd'
                ...
                if (f) {
                        if (!(f->f_mode & FMODE_WRITE))
                                goto mnt_drop_write_and_out;

The check should instead be based on the file permissions.

Thanks to Miklos for pointing out how to do this check.
Miklos also pointed out a simplification that could be
made to my first version of this patch, since the checks
for the pathname and file descriptor cases can now be
conflated.

Acked-by: Miklos Szeredi 
Cc: Al Viro 
Cc: Ulrich Drepper 
Signed-off-by: Michael Kerrisk 
Signed-off-by: Andrew Morton 
Signed-off-by: Al Viro

[patch for 2.6.26 3/4] vfs: utimensat(): fix error checking for {UTIME_NOW,UTIME_OMIT} case

2008-06-23T12:43:04+00:00

The POSIX.1 draft spec for utimensat() says:

    Only a process with the effective user ID equal to the
    user ID of the file or with appropriate privileges may use
    futimens() or utimensat() with a non-null times argument
    that does not have both tv_nsec fields set to UTIME_NOW
    and does not have both tv_nsec fields set to UTIME_OMIT.

If this condition is violated, then the error EPERM should result.
However, the current implementation does not generate EPERM if
one tv_nsec field is UTIME_NOW while the other is UTIME_OMIT.
It should give this error for that case.

This patch:

a) Repairs that problem.
b) Removes the now unneeded nsec_special() helper function.
c) Adds some comments to explain the checks that are being
   performed.

Thanks to Miklos, who provided comments on the previous iteration
of this patch.  As a result, this version is a little simpler and
and its logic is better structured.

Miklos suggested an alternative idea, migrating the
is_owner_or_cap() checks into fs/attr.c:inode_change_ok() via
the use of an ATTR_OWNER_CHECK flag.  Maybe we could do that
later, but for now I've gone with this version, which is
IMO simpler, and can be more easily read as being correct.

Acked-by: Miklos Szeredi 
Cc: Al Viro 
Cc: Ulrich Drepper 
Signed-off-by: Michael Kerrisk 
Signed-off-by: Andrew Morton 
Signed-off-by: Al Viro

[patch for 2.6.26 1/4] vfs: utimensat(): ignore tv_sec if tv_nsec == UTIME_OMIT or UTIME_NOW

2008-06-23T12:43:04+00:00

The POSIX.1 draft spec for utimensat() says that if a times[n].tv_nsec
field is UTIME_OMIT or UTIME_NOW, then the value in the corresponding
tv_sec field is ignored.  See the last sentence of this para, from
the spec:

    If the tv_nsec field of a timespec structure has
    the special value UTIME_NOW, the file's relevant
    timestamp shall be set to the greatest value
    supported by the file system that is not greater than
    the current time. If the tv_nsec field has the
    special value UTIME_OMIT, the file's relevant
    timestamp shall not be changed. In either case,
    the tv_sec field shall be ignored.

However the current Linux implementation requires the tv_sec value to be
zero (or the EINVAL error results). This requirement should be removed.

Acked-by: Miklos Szeredi 
Cc: Al Viro 
Cc: Ulrich Drepper 
Signed-off-by: Michael Kerrisk 
Signed-off-by: Andrew Morton 
Signed-off-by: Al Viro

[patch for 2.6.26 2/4] vfs: utimensat(): be consistent with utime() for immutable and append-only files

2008-06-23T12:43:03+00:00

This patch fixes utimensat() to make its behavior consistent
with that of utime()/utimes() when dealing with files marked
immutable and append-only.

The current utimensat() implementation also returns EPERM if
'times' is non-NULL and the tv_nsec fields are both UTIME_NOW.
For consistency, the

(times != NULL && times[0].tv_nsec == UTIME_NOW &&
                  times[1].tv_nsec == UTIME_NOW)

case should be treated like the traditional utimes() case where
'times' is NULL.  That is, the call should succeed for a file
marked append-only and should give the error EACCES if the file
is marked as immutable.

The simple way to do this is to set 'times' to NULL
if (times[0].tv_nsec == UTIME_NOW && times[1].tv_nsec == UTIME_NOW).

This is also the natural approach, since POSIX.1 semantics consider the
times == {{x, UTIME_NOW}, {y, UTIME_NOW}}
to be exactly equivalent to the case for
times == NULL.

(Thanks to Miklos for pointing this out.)

Patch 3 in this series relies on the simplification provided
by this patch.

Acked-by: Miklos Szeredi 
Cc: Al Viro 
Cc: Ulrich Drepper 
Signed-off-by: Michael Kerrisk 
Signed-off-by: Andrew Morton 
Signed-off-by: Al Viro

vfs: fix permission checking in sys_utimensat

2008-05-01T15:03:59+00:00

If utimensat() is called with both times set to UTIME_NOW or one of them to
UTIME_NOW and the other to UTIME_OMIT, then it will update the file time
without any permission checking.

I don't think this can be used for anything other than a local DoS, but could
be quite bewildering at that (e.g.  "Why was that large source tree rebuilt
when I didn't modify anything???")

This affects all kernels from 2.6.22, when the utimensat() syscall was
introduced.

Fix by doing the same permission checking as for the "times == NULL" case.

Thanks to Michael Kerrisk, whose utimensat-non-conformances-and-fixes.patch in
-mm also fixes this (and breaks other stuff), only he didn't realize the
security implications of this bug.

Signed-off-by: Miklos Szeredi 
Cc: Ulrich Drepper 
Cc: Michael Kerrisk 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] r/o bind mounts: elevate write count for do_utimes()

2008-04-19T04:29:24+00:00

Now includes fix for oops seen by akpm.

"never let a libc developer write your kernel code" - hch

"nor, apparently, a kernel developer" - akpm

Acked-by: Al Viro 
Signed-off-by: Christoph Hellwig 
Cc: Valdis Kletnieks 
Cc: Balbir Singh 
Signed-off-by: Dave Hansen 
Signed-off-by: Al Viro

Introduce path_put()

2008-02-15T05:13:33+00:00

* Add path_put() functions for releasing a reference to the dentry and
  vfsmount of a struct path in the right order

* Switch from path_release(nd) to path_put(&nd->path)

* Rename dput_path() to path_put_conditional()

[akpm@linux-foundation.org: fix cifs]
Signed-off-by: Jan Blunck 
Signed-off-by: Andreas Gruenbacher 
Acked-by: Christoph Hellwig 
Cc: 
Cc: Al Viro 
Cc: Steven French 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Embed a struct path into struct nameidata instead of nd->{dentry,mnt}

2008-02-15T05:13:33+00:00

This is the central patch of a cleanup series. In most cases there is no good
reason why someone would want to use a dentry for itself. This series reflects
that fact and embeds a struct path into nameidata.

Together with the other patches of this series
- it enforced the correct order of getting/releasing the reference count on
   pairs
- it prepares the VFS for stacking support since it is essential to have a
  struct path in every place where the stack can be traversed
- it reduces the overall code size:

without patch series:
   text    data     bss     dec     hex filename
5321639  858418  715768 6895825  6938d1 vmlinux

with patch series:
   text    data     bss     dec     hex filename
5320026  858418  715768 6894212  693284 vmlinux

This patch:

Switch from nd->{dentry,mnt} to nd->path.{dentry,mnt} everywhere.

[akpm@linux-foundation.org: coding-style fixes]
[akpm@linux-foundation.org: fix cifs]
[akpm@linux-foundation.org: fix smack]
Signed-off-by: Jan Blunck 
Signed-off-by: Andreas Gruenbacher 
Acked-by: Christoph Hellwig 
Cc: Al Viro 
Cc: Casey Schaufler 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

fs/utimes.c should #include

2008-02-06T18:41:03+00:00

Every file should include the headers containing the prototypes for its global
functions.

Signed-off-by: Adrian Bunk 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

VFS: check nanoseconds in utimensat

2007-10-17T15:42:52+00:00

utimensat() (and possibly other callers of do_utimes()) didn't check if the
nanosecond value was within the allowed range.

Signed-off-by: Miklos Szeredi 
Cc: Ulrich Drepper 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds