[PATCH 4.4 34/47] userns: move user access out of the mutex
Rafael David Tinoco
rafael.tinoco at linaro.org
Sun Sep 9 03:56:45 UTC 2018
On Fri, Sep 7, 2018 at 6:41 PM Greg Kroah-Hartman
<gregkh at linuxfoundation.org> wrote:
> 4.4-stable review patch. If anyone has any objections, please let me know.
> From: Jann Horn <jannh at 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 at vger.kernel.org
> Signed-off-by: Jann Horn <jannh at google.com>
> Acked-by: Christian Brauner <christian at brauner.io>
> Acked-by: Serge Hallyn <serge at hallyn.com>
> Signed-off-by: Eric W. Biederman <ebiederm at xmission.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh at 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):
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()
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.
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