On Tue, Apr 2, 2024 at 12:12 AM Steve French <smfrench@xxxxxxxxx> wrote:
>
> tentatively merged into cifs-2.6.git for-next pending additional
> testing and review
>
> On Mon, Apr 1, 2024 at 12:13 PM Paulo Alcantara <pc@xxxxxxxxxxxxx> wrote:
> >
> > The UAF bug is due to smb2_reconnect_server() accessing a session that
> > is already being teared down by another thread that is executing
> > __cifs_put_smb_ses(). This can happen when (a) the client has
> > connection to the server but no session or (b) another thread ends up
> > setting @ses->ses_status again to something different than
> > SES_EXITING.
> >
> > To fix this, we need to make sure to unconditionally set
> > @ses->ses_status to SES_EXITING and prevent any other threads from
> > setting a new status while we're still tearing it down.
> >
> > The following can be reproduced by adding some delay to right after
> > the ipc is freed in __cifs_put_smb_ses() - which will give
> > smb2_reconnect_server() worker a chance to run and then accessing
> > @ses->ipc:
> >
> > kinit ...
> > mount.cifs //srv/share /mnt/1 -o sec=krb5,nohandlecache,echo_interval=10
> > [disconnect srv]
> > ls /mnt/1 &>/dev/null
> > sleep 30
> > kdestroy
> > [reconnect srv]
> > sleep 10
> > umount /mnt/1
> > ...
> > CIFS: VFS: Verify user has a krb5 ticket and keyutils is installed
> > CIFS: VFS: \\srv Send error in SessSetup = -126
> > CIFS: VFS: Verify user has a krb5 ticket and keyutils is installed
> > CIFS: VFS: \\srv Send error in SessSetup = -126
> > general protection fault, probably for non-canonical address
> > 0x6b6b6b6b6b6b6b6b: 0000 [#1] PREEMPT SMP NOPTI
> > CPU: 3 PID: 50 Comm: kworker/3:1 Not tainted 6.9.0-rc2 #1
> > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-1.fc39
> > 04/01/2014
> > Workqueue: cifsiod smb2_reconnect_server [cifs]
> > RIP: 0010:__list_del_entry_valid_or_report+0x33/0xf0
> > Code: 4f 08 48 85 d2 74 42 48 85 c9 74 59 48 b8 00 01 00 00 00 00 ad
> > de 48 39 c2 74 61 48 b8 22 01 00 00 00 00 74 69 <48> 8b 01 48 39 f8 75
> > 7b 48 8b 72 08 48 39 c6 0f 85 88 00 00 00 b8
> > RSP: 0018:ffffc900001bfd70 EFLAGS: 00010a83
> > RAX: dead000000000122 RBX: ffff88810da53838 RCX: 6b6b6b6b6b6b6b6b
> > RDX: 6b6b6b6b6b6b6b6b RSI: ffffffffc02f6878 RDI: ffff88810da53800
> > RBP: ffff88810da53800 R08: 0000000000000001 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000001 R12: ffff88810c064000
> > R13: 0000000000000001 R14: ffff88810c064000 R15: ffff8881039cc000
> > FS: 0000000000000000(0000) GS:ffff888157c00000(0000)
> > knlGS:0000000000000000
> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00007fe3728b1000 CR3: 000000010caa4000 CR4: 0000000000750ef0
> > PKRU: 55555554
> > Call Trace:
> > <TASK>
> > ? die_addr+0x36/0x90
> > ? exc_general_protection+0x1c1/0x3f0
> > ? asm_exc_general_protection+0x26/0x30
> > ? __list_del_entry_valid_or_report+0x33/0xf0
> > __cifs_put_smb_ses+0x1ae/0x500 [cifs]
> > smb2_reconnect_server+0x4ed/0x710 [cifs]
> > process_one_work+0x205/0x6b0
> > worker_thread+0x191/0x360
> > ? __pfx_worker_thread+0x10/0x10
> > kthread+0xe2/0x110
> > ? __pfx_kthread+0x10/0x10
> > ret_from_fork+0x34/0x50
> > ? __pfx_kthread+0x10/0x10
> > ret_from_fork_asm+0x1a/0x30
> > </TASK>
> >
> > Signed-off-by: Paulo Alcantara (Red Hat) <pc@xxxxxxxxxxxxx>
> > ---
> > v1 -> v2: add missing comments in reproducer
> >
> > fs/smb/client/connect.c | 87 +++++++++++++++++------------------------
> > 1 file changed, 36 insertions(+), 51 deletions(-)
> >
> > diff --git a/fs/smb/client/connect.c b/fs/smb/client/connect.c
> > index 9b85b5341822..ee29bc57300c 100644
> > --- a/fs/smb/client/connect.c
> > +++ b/fs/smb/client/connect.c
> > @@ -232,7 +232,13 @@ cifs_mark_tcp_ses_conns_for_reconnect(struct TCP_Server_Info *server,
> >
> > spin_lock(&cifs_tcp_ses_lock);
> > list_for_each_entry_safe(ses, nses, &pserver->smb_ses_list, smb_ses_list) {
> > - /* check if iface is still active */
> > + spin_lock(&ses->ses_lock);
> > + if (ses->ses_status == SES_EXITING) {
> > + spin_unlock(&ses->ses_lock);
> > + continue;
> > + }
> > + spin_unlock(&ses->ses_lock);
> > +
I'm beginning to contemplate whether this function should be dealing
with changes to ses and tcon states at all?
Since it always gets called by cifsd thread, I suspect that it could
lead to race conditions that are hard to handle.
If we move
But that change can be a different patch.
> > spin_lock(&ses->chan_lock);
> > if (cifs_ses_get_chan_index(ses, server) ==
> > CIFS_INVAL_CHAN_INDEX) {
> > @@ -1963,31 +1969,6 @@ cifs_setup_ipc(struct cifs_ses *ses, struct smb3_fs_context *ctx)
> > return rc;
> > }
> >
> > -/**
> > - * cifs_free_ipc - helper to release the session IPC tcon
> > - * @ses: smb session to unmount the IPC from
> > - *
> > - * Needs to be called everytime a session is destroyed.
> > - *
> > - * On session close, the IPC is closed and the server must release all tcons of the session.
> > - * No need to send a tree disconnect here.
> > - *
> > - * Besides, it will make the server to not close durable and resilient files on session close, as
> > - * specified in MS-SMB2 3.3.5.6 Receiving an SMB2 LOGOFF Request.
> > - */
> > -static int
> > -cifs_free_ipc(struct cifs_ses *ses)
> > -{
> > - struct cifs_tcon *tcon = ses->tcon_ipc;
> > -
> > - if (tcon == NULL)
> > - return 0;
> > -
> > - tconInfoFree(tcon);
> > - ses->tcon_ipc = NULL;
> > - return 0;
> > -}
> > -
Why was removal of this function needed?
> > static struct cifs_ses *
> > cifs_find_smb_ses(struct TCP_Server_Info *server, struct smb3_fs_context *ctx)
> > {
> > @@ -2019,48 +2000,52 @@ cifs_find_smb_ses(struct TCP_Server_Info *server, struct smb3_fs_context *ctx)
> > void __cifs_put_smb_ses(struct cifs_ses *ses)
> > {
> > struct TCP_Server_Info *server = ses->server;
> > + struct cifs_tcon *tcon;
> > unsigned int xid;
> > size_t i;
> > + bool do_logoff;
> > int rc;
> >
> > - spin_lock(&ses->ses_lock);
> > - if (ses->ses_status == SES_EXITING) {
> > - spin_unlock(&ses->ses_lock);
> > - return;
> > - }
> > - spin_unlock(&ses->ses_lock);
> > -
> > - cifs_dbg(FYI, "%s: ses_count=%d\n", __func__, ses->ses_count);
> > - cifs_dbg(FYI,
> > - "%s: ses ipc: %s\n", __func__, ses->tcon_ipc ? ses->tcon_ipc->tree_name : "NONE");
> > -
> > spin_lock(&cifs_tcp_ses_lock);
> > - if (--ses->ses_count > 0) {
> > + spin_lock(&ses->ses_lock);
> > + cifs_dbg(FYI, "%s: id=0x%llx ses_count=%d ses_status=%u ipc=%s\n",
> > + __func__, ses->Suid, ses->ses_count, ses->ses_status,
> > + ses->tcon_ipc ? ses->tcon_ipc->tree_name : "none");
> > + if (ses->ses_status == SES_EXITING || --ses->ses_count > 0) {
> > + spin_unlock(&ses->ses_lock);
> > spin_unlock(&cifs_tcp_ses_lock);
> > return;
> > }
> > - spin_lock(&ses->ses_lock);
> > - if (ses->ses_status == SES_GOOD)
> > - ses->ses_status = SES_EXITING;
> > - spin_unlock(&ses->ses_lock);
> > - spin_unlock(&cifs_tcp_ses_lock);
> > -
> > /* ses_count can never go negative */
> > WARN_ON(ses->ses_count < 0);
> >
> > - spin_lock(&ses->ses_lock);
> > - if (ses->ses_status == SES_EXITING && server->ops->logoff) {
> > - spin_unlock(&ses->ses_lock);
> > - cifs_free_ipc(ses);
> > + spin_lock(&ses->chan_lock);
> > + cifs_chan_clear_need_reconnect(ses, server);
> > + spin_unlock(&ses->chan_lock);
> > +
> > + do_logoff = ses->ses_status == SES_GOOD && server->ops->logoff;
> > + ses->ses_status = SES_EXITING;
> > + tcon = ses->tcon_ipc;
> > + ses->tcon_ipc = NULL;
> > + spin_unlock(&ses->ses_lock);
> > + spin_unlock(&cifs_tcp_ses_lock);
> > +
> > + /*
> > + * On session close, the IPC is closed and the server must release all
> > + * tcons of the session. No need to send a tree disconnect here.
> > + *
> > + * Besides, it will make the server to not close durable and resilient
> > + * files on session close, as specified in MS-SMB2 3.3.5.6 Receiving an
> > + * SMB2 LOGOFF Request.
> > + */
> > + tconInfoFree(tcon);
> > + if (do_logoff) {
> > xid = get_xid();
> > rc = server->ops->logoff(xid, ses);
> > if (rc)
> > cifs_server_dbg(VFS, "%s: Session Logoff failure rc=%d\n",
> > __func__, rc);
> > _free_xid(xid);
> > - } else {
> > - spin_unlock(&ses->ses_lock);
> > - cifs_free_ipc(ses);
> > }
> >
> > spin_lock(&cifs_tcp_ses_lock);
> > --
> > 2.44.0
> >
>
>
> --
> Thanks,
>
> Steve
>
--
Regards,
Shyam
