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);
> +
> 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;
> -}
> -
> 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
