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

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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 <miklos@szeredi.hu>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Ulrich Drepper <drepper@redhat.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Michael Kerrisk 2008-06-09 21:16:08 -07:00 committed by Al Viro
parent 94c70b9ba7
commit 4cca92264e
1 changed files with 21 additions and 15 deletions
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36
fs/utimes.c
View file

@ -40,14 +40,9 @@ asmlinkage long sys_utime(char __user *filename, struct utimbuf __user *times)
#endif
static bool nsec_special(long nsec)
{
return nsec == UTIME_OMIT || nsec == UTIME_NOW;
}
static bool nsec_valid(long nsec)
{
if (nsec_special(nsec))
if (nsec == UTIME_OMIT || nsec == UTIME_NOW)
return true;
return nsec >= 0 && nsec <= 999999999;
@ -106,7 +101,7 @@ long do_utimes(int dfd, char __user *filename, struct timespec *times, int flags
times[1].tv_nsec == UTIME_NOW)
times = NULL;
/* Don't worry, the checks are done in inode_change_ok() */
/* In most cases, the checks are done in inode_change_ok() */
newattrs.ia_valid = ATTR_CTIME | ATTR_MTIME | ATTR_ATIME;
if (times) {
error = -EPERM;
@ -128,15 +123,26 @@ long do_utimes(int dfd, char __user *filename, struct timespec *times, int flags
newattrs.ia_mtime.tv_nsec = times[1].tv_nsec;
newattrs.ia_valid |= ATTR_MTIME_SET;
}
}
/*
* If times is NULL or both times are either UTIME_OMIT or
* UTIME_NOW, then need to check permissions, because
* inode_change_ok() won't do it.
*/
if (!times || (nsec_special(times[0].tv_nsec) &&
nsec_special(times[1].tv_nsec))) {
/*
* For the UTIME_OMIT/UTIME_NOW and UTIME_NOW/UTIME_OMIT
* cases, we need to make an extra check that is not done by
* inode_change_ok().
*/
if (((times[0].tv_nsec == UTIME_NOW &&
times[1].tv_nsec == UTIME_OMIT)
||
(times[0].tv_nsec == UTIME_OMIT &&
times[1].tv_nsec == UTIME_NOW))
&& !is_owner_or_cap(inode))
goto mnt_drop_write_and_out;
} else {
/*
* If times is NULL (or both times are UTIME_NOW),
* then we need to check permissions, because
* inode_change_ok() won't do it.
*/
error = -EACCES;
if (IS_IMMUTABLE(inode))
goto mnt_drop_write_and_out;