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Date: Mon, 12 May 2014 00:53:50 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: miklos@...redi.hu, jmorris@...ei.org, john.johansen@...onical.com
Cc: selinux@...ho.nsa.gov, linux-security-module@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
torvalds@...ux-foundation.org
Subject: Re: [PATCH (for 3.15) 0/5] Fix cross rename race window for LSM.
Miklos, I have a question regarding renameat2(RENAME_EXCHANGE).
renameat2(RENAME_EXCHANGE) allows exchanging a directory and a non-directory,
doesn't it? If yes, TOMOYO and AppArmor got a regression bug described below.
TOMOYO and AppArmor handle pathnames of a directory and a non-directory
differently. It is considered as a directory's pathname if the pathname ends
with / , and it is considered as a non-directory's pathname if the pathname
does not end with / .
Until renameat2(RENAME_EXCHANGE) was introduced, if the old_dentry refers a
directory, it is guaranteed that the new_dentry will refer a directory upon
successful rename() operation. Therefore, TOMOYO and AppArmor automatically
appended / to the pathname calculated from new_dentry based on
S_ISDIR(old_dentry->d_inode->i_mode).
int tomoyo_path2_perm(const u8 operation, struct path *path1,
struct path *path2)
{
(...snipped...)
if (!tomoyo_get_realpath(&buf1, path1) ||
!tomoyo_get_realpath(&buf2, path2))
goto out;
switch (operation) {
struct dentry *dentry;
case TOMOYO_TYPE_RENAME:
case TOMOYO_TYPE_LINK:
dentry = path1->dentry;
if (!dentry->d_inode || !S_ISDIR(dentry->d_inode->i_mode))
break;
/* fall through */
case TOMOYO_TYPE_PIVOT_ROOT:
tomoyo_add_slash(&buf1);
tomoyo_add_slash(&buf2);
break;
}
(...snipped...)
}
static int apparmor_path_rename(struct path *old_dir, struct dentry *old_dentry,
struct path *new_dir, struct dentry *new_dentry)
{
(...snipped...)
struct path_cond cond = { old_dentry->d_inode->i_uid,
old_dentry->d_inode->i_mode
};
error = aa_path_perm(OP_RENAME_SRC, profile, &old_path, 0,
MAY_READ | AA_MAY_META_READ | MAY_WRITE |
AA_MAY_META_WRITE | AA_MAY_DELETE,
&cond);
if (!error)
error = aa_path_perm(OP_RENAME_DEST, profile, &new_path,
0, MAY_WRITE | AA_MAY_META_WRITE |
AA_MAY_CREATE, &cond);
(...snipped...)
}
Now, as renameat2(RENAME_EXCHANGE) is introduced, it is no longer guaranteed
that the new_dentry will refer a directory upon successful
renameat2(RENAME_EXCHANGE) because renameat2(RENAME_EXCHANGE) allows exchanging
a directory's pathname and a non-directory's pathname. TOMOYO and AppArmor can
no longer automatically append / to the pathname calculated from new_dentry
based on S_ISDIR(old_dentry->d_inode->i_mode).
To fix this problem, TOMOYO and AppArmor need to receive the flags argument and
use S_ISDIR(new_dentry->d_inode->i_mode) if renameat2(RENAME_EXCHANGE) and use
S_ISDIR(old_dentry->d_inode->i_mode) if renameat2(!RENAME_EXCHANGE).
Regarding TOMOYO, "[PATCH (for 3.15) 4/5] TOMOYO: Handle the rename flags." can
fix this problem. Regarding AppArmor, we need to update
"[PATCH (for 3.15) 3/5] AppArmor: Handle the rename flags.".
Anyway, James, can we merge
"[PATCH (for 3.15) 1/5] LSM: Pass the rename flags to each LSM module." now?
Tetsuo Handa wrote:
> Hello SELinux people, may I have your response?
>
> Miklos Szeredi posted v3 of cross rename patchset at
> http://marc.info/?l=linux-fsdevel&m=138921924707564&w=4 . In that thread,
> I questioned him whether he already explained this proposal to LSM people.
> He answered no and explained me what renameat2() does. I asked him to get
> confirmation from LSM people before he merges this change to linux-next.git
> tree, and he answered that patch 07/11 already does what LSM people need. But
> I commented that TOMOYO wants to avoid re-calculation of pathnames and posted
> a patch at http://marc.info/?l=linux-security-module&m=138970469226106&w=4 and
> John Johansen commented that the changes in AppArmor directory looks OK and
> John would re-factor AppArmor to avoid re-calculation in the future. Therefore,
> I posted a patch for SELinux/SMACK/Capability at
> http://marc.info/?l=linux-fsdevel&m=138973289404450&w=4 but Miklos responded
> that he doesn't want to include my patch which temporarily breaks TOMOYO and
> AppArmor. Instead, he asked me to post a complete patch right after his cross
> rename patchset goes in. Thus, I was waiting for his cross rename patchset to
> arrive at linux-next.git tree.
>
> By the day Linux 3.14 was released, Miklos's cross rename patchset did not
> arrive at linux-next.git tree. Therefore, I assumed that the cross rename
> patchset will not go to Linux 3.15-rc1. However, the patchset committed after
> Linux 3.14 release (commit da1ce067 "vfs: add cross-rename") directly went to
> linux.git tree without letting it known to LSM people and the merge window for
> Linux 3.15 was closed. Then, I noticed that renameat2() will be in 3.15 at
> http://marc.info/?l=linux-fsdevel&m=139789855823422&w=2 .
>
> At first, I assumed that renameat2() is not callable as of 3.15 because I
> couldn't find "#define __NR_renameat2" line. But Miklos told me that
> renameat2() will be callable as of 3.15 because x86 automatically generates
> __NR_renameat2 entries. I realized that TOMOYO and AppArmor now have a race
> window (a kind of regression) introduced by the cross rename functionality, and
> I re-posted my patch as a patchset in this thread. I can approve the changes in
> TOMOYO directory and John Johansen already gave me a sort of Reviewed-by:
> response to the changes in AppArmor directory in January's thread. In this
> thread, Casey Schaufler gave me an Acked-by: response to the changes in SMACK
> directory, but so far I have gotten no response from SELinux people.
>
> Would somebody in SELinux community please respond to the changes in SELinux
> directory so that we can merge this race window fix patchset before 3.15-final?
>
> Regards.
>
> Tetsuo Handa wrote:
> > James, would you send this patchset to Linus?
> > This patchset is expected to go to 3.15 because this is a kind of regression fix.
> >
> > Tetsuo Handa wrote:
> > > Miklos Szeredi wrote:
> > > > On Sat, Apr 19, 2014 at 2:08 PM, Tetsuo Handa
> > > > <penguin-kernel@...ove.sakura.ne.jp> wrote:
> > > > > Michael Kerrisk (man-pages) wrote:
> > > > >> Now that renameat2() is in 3.15, I've taken these changes.
> > > > >
> > > > > What!? I didn't know renameat2() goes to 3.15.
> > > > >
> > > > > But I assume that renameat2() is not accessible in 3.15, for I can see
> > > > > "asmlinkage long sys_renameat2(" but don't see "#define __NR_renameat2".
> > > >
> > > > x86 automatically generates __NR_foo entries and syscall tables from
> > > > arch/x86/syscalls/syscall_*.tbl, which is why you don't find an
> > > > explicit definition in the git tree.
> > > >
> > > > Thanks,
> > > > Miklos
> > > >
> > >
> > > Oh, I see. Then, I must submit patches for fixing a race window
> > > caused by commit da1ce067 "vfs: add cross-rename".
> > >
> > > Regards.
> > >
> >
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