Messages in this thread | | | From | Rafael David Tinoco <> | Date | Sun, 9 Sep 2018 00:56:45 -0300 | Subject | Re: [PATCH 4.4 34/47] userns: move user access out of the mutex |
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Greg,
On Fri, Sep 7, 2018 at 6:41 PM Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote: > > 4.4-stable review patch. If anyone has any objections, please let me know. > > ------------------ > > From: Jann Horn <jannh@google.com> > > commit 5820f140edef111a9ea2ef414ab2428b8cb805b1 upstream. > > The old code would hold the userns_state_mutex indefinitely if > memdup_user_nul stalled due to e.g. a userfault region. Prevent that by > moving the memdup_user_nul in front of the mutex_lock(). > > Note: This changes the error precedence of invalid buf/count/*ppos vs > map already written / capabilities missing. > > Fixes: 22d917d80e84 ("userns: Rework the user_namespace adding uid/gid...") > Cc: stable@vger.kernel.org > Signed-off-by: Jann Horn <jannh@google.com> > Acked-by: Christian Brauner <christian@brauner.io> > Acked-by: Serge Hallyn <serge@hallyn.com> > Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > > --- > kernel/user_namespace.c | 22 ++++++++++------------ > 1 file changed, 10 insertions(+), 12 deletions(-) > > --- a/kernel/user_namespace.c > +++ b/kernel/user_namespace.c > @@ -604,7 +604,16 @@ static ssize_t map_write(struct file *fi > struct uid_gid_extent *extent = NULL; > unsigned long page = 0; > char *kbuf, *pos, *next_line; > - ssize_t ret = -EINVAL; > + ssize_t ret; > + > + /* Only allow < page size writes at the beginning of the file */ > + if ((*ppos != 0) || (count >= PAGE_SIZE)) > + return -EINVAL; > + > + /* Slurp in the user data */ > + if (copy_from_user(kbuf, buf, count)) > + return -EFAULT; > + kbuf[count] = '\0';
Naresh will soon report issues found by LKFT on user_ns for 4.4 kernel for this review round.
selftests: mount_run_tests.sh [FAIL] write to /proc/self/uid_map failed: Bad address
LTP: user_namespace2 1 TBROK : safe_macros.c:452: userns02.c:95: write(6,0x7ffc133113d0,18446744073709551615) failed: errno=EFAULT(14): Bad address
I believe the EFAULT was caused because when changing code from "memdup_user_nul" to "copy_from_user", for the older kernels, you missed allocating the slab object for "kbuf", like memdup_user_nul() does.
Note: This likely applies to 3.18 as well.
We are finishing functional tests without this patch, but we wanted to make you aware right away.
Best Regards, Rafael
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