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
ls /mnt/1 &>/dev/null
sleep 30
kdestroy
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>
---
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
