On Tue, 2018-05-15 at 09:06 -0400, David Wysochanski wrote:
> On Tue, 2018-04-17 at 16:11 -0400, Dave Wysochanski wrote:
> > In nfs_idmap_read_and_verify_message there is an unprotected
> > sprintf
> > that converts the __u32 'im_id' from struct idmap_msg to 'id_str'
> > that is a stack variable of 'NFS_UINT_MAXLEN' (defined as 11).
> > If a uid or gid value is > 2147483647 = 0x7fffffff we corrupt
> > kernel memory by one byte and if CONFIG_CC_STACKPROTECTOR_STRONG
> > is set we see a stack-protector panic as follows:
> >
> > [11558053.616565] Kernel panic - not syncing: stack-protector:
> > Kernel stack is corrupted in: ffffffffa05b8a8c
> >
> > [11558053.639063] CPU: 6 PID: 9423 Comm: rpc.idmapd Tainted:
> > G W ------------ T 3.10.0-514.el7.x86_64 #1
> > [11558053.641990] Hardware name: Red Hat OpenStack Compute, BIOS
> > 1.10.2-3.el7_4.1 04/01/2014
> > [11558053.644462] ffffffff818c7bc0 00000000b1f3aec1
> > ffff880de0f9bd48 ffffffff81685eac
> > [11558053.646430] ffff880de0f9bdc8 ffffffff8167f2b3
> > ffffffff00000010 ffff880de0f9bdd8
> > [11558053.648313] ffff880de0f9bd78 00000000b1f3aec1
> > ffffffff811dcb03 ffffffffa05b8a8c
> > [11558053.650107] Call Trace:
> > [11558053.651347] [<ffffffff81685eac>] dump_stack+0x19/0x1b
> > [11558053.653013] [<ffffffff8167f2b3>] panic+0xe3/0x1f2
> > [11558053.666240] [<ffffffff811dcb03>] ? kfree+0x103/0x140
> > [11558053.682589] [<ffffffffa05b8a8c>] ?
> > idmap_pipe_downcall+0x1cc/0x1e0 [nfsv4]
> > [11558053.689710] [<ffffffff810855db>] __stack_chk_fail+0x1b/0x30
> > [11558053.691619] [<ffffffffa05b8a8c>]
> > idmap_pipe_downcall+0x1cc/0x1e0 [nfsv4]
> > [11558053.693867] [<ffffffffa00209d6>] rpc_pipe_write+0x56/0x70
> > [sunrpc]
> > [11558053.695763] [<ffffffff811fe12d>] vfs_write+0xbd/0x1e0
> > [11558053.702236] [<ffffffff810acccc>] ? task_work_run+0xac/0xe0
> > [11558053.704215] [<ffffffff811fec4f>] SyS_write+0x7f/0xe0
> > [11558053.709674] [<ffffffff816964c9>]
> > system_call_fastpath+0x16/0x1b
> >
> > Fix this by snprintf and a safe length based on sizeof(id_str).
> >
> > Signed-off-by: Dave Wysochanski <dwysocha@xxxxxxxxxx>
> > Reported-by: Stephen Johnston <sjohnsto@xxxxxxxxxx>
> > ---
> > fs/nfs/nfs4idmap.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/nfs/nfs4idmap.c b/fs/nfs/nfs4idmap.c
> > index 22dc30a679a0..a8c663f8dd99 100644
> > --- a/fs/nfs/nfs4idmap.c
> > +++ b/fs/nfs/nfs4idmap.c
> > @@ -627,7 +627,7 @@ static int
> > nfs_idmap_read_and_verify_message(struct idmap_msg *im,
> > if (strcmp(upcall->im_name, im->im_name) != 0)
> > break;
> > /* Note: here we store the NUL terminator too */
> > - len = sprintf(id_str, "%d", im->im_id) + 1;
> > + len = snprintf(id_str, sizeof(id_str), "%u", im-
> > >im_id) + 1;
> > ret = nfs_idmap_instantiate(key, authkey, id_str,
> > len);
> > break;
> > case IDMAP_CONV_IDTONAME:
>
>
> I did not see any reply to this and we did have one customer hit this
> which caused a considerable outage of many machines. In essence once
> this happened, it became a DoS on all machines using idmapping and
> they
> implemented a temporary workaround.
>
> Anna / Trond - if you need me to improve the patch header or want
> clarification or see a problem with it, please let me know.
>
If the value of NFS_UINT_MAXLEN is too small, then shouldn't we be
increasing it? That would appear to be the real bug here.
I do agree that the "%d" should be changed to "%u", though. Isn't that
sufficient to make the buffer large enough?
Cheers
Trond
--
Trond Myklebust
CTO, Hammerspace Inc
4300 El Camino Real, Suite 105
Los Altos, CA 94022
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