[PATCH v4 1/4] Bluetooth: Fix potential double free caused by hci_conn_unlink

[PATCH v4 1/4] Bluetooth: Fix potential double free caused by hci_conn_unlink

[Ruihan Li]

The hci_conn_unlink function is being called by hci_conn_del, which
means it should not call hci_conn_del with the input parameter conn
again. If it does, conn may have already been released when
hci_conn_unlink returns, leading to potential UAF and double-free
issues.

This patch resolves the problem by modifying hci_conn_unlink to release
only conn's child links when necessary, but never release conn itself.

Reported-by: syzbot+690b90b14f14f43f4688@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-bluetooth/000000000000484a8205faafe216@google.com/
Fixes: 06149746e720 ("Bluetooth: hci_conn: Add support for linking multiple hcon")
Signed-off-by: Ruihan Li <lrh2000@pku.edu.cn>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
---
  * Fix tags in commit messages. No code was changed.

 net/bluetooth/hci_conn.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index 640b951bf..70e1655a9 100644
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -1083,8 +1083,18 @@ static void hci_conn_unlink(struct hci_conn *conn)
 	if (!conn->parent) {
 		struct hci_link *link, *t;
 
-		list_for_each_entry_safe(link, t, &conn->link_list, list)
-			hci_conn_unlink(link->conn);
+		list_for_each_entry_safe(link, t, &conn->link_list, list) {
+			struct hci_conn *child = link->conn;
+
+			hci_conn_unlink(child);
+
+			/* Due to race, SCO connection might be not established
+			 * yet at this point. Delete it now, otherwise it is
+			 * possible for it to be stuck and can't be deleted.
+			 */
+			if (child->handle == HCI_CONN_HANDLE_UNSET)
+				hci_conn_del(child);
+		}
 
 		return;
 	}
@@ -1100,13 +1110,6 @@ static void hci_conn_unlink(struct hci_conn *conn)
 
 	kfree(conn->link);
 	conn->link = NULL;
-
-	/* Due to race, SCO connection might be not established
-	 * yet at this point. Delete it now, otherwise it is
-	 * possible for it to be stuck and can't be deleted.
-	 */
-	if (conn->handle == HCI_CONN_HANDLE_UNSET)
-		hci_conn_del(conn);
 }
 
 int hci_conn_del(struct hci_conn *conn)
-- 
2.40.0

[PATCH v4 2/4] Bluetooth: Refcnt drop must be placed last in hci_conn_unlink

[Ruihan Li]

If hci_conn_put(conn->parent) reduces conn->parent's reference count to
zero, it can immediately deallocate conn->parent. At the same time,
conn->link->list has its head in conn->parent, causing use-after-free
problems in the latter list_del_rcu(&conn->link->list).

This problem can be easily solved by reordering the two operations,
i.e., first performing the list removal with list_del_rcu and then
decreasing the refcnt with hci_conn_put.

Reported-by: Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Closes: https://lore.kernel.org/linux-bluetooth/CABBYNZ+1kce8_RJrLNOXd_8=Mdpb=2bx4Nto-hFORk=qiOkoCg@mail.gmail.com/
Fixes: 06149746e720 ("Bluetooth: hci_conn: Add support for linking multiple hcon")
Signed-off-by: Ruihan Li <lrh2000@pku.edu.cn>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
---
 net/bluetooth/hci_conn.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index 70e1655a9..44d0643fc 100644
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -1102,12 +1102,12 @@ static void hci_conn_unlink(struct hci_conn *conn)
 	if (!conn->link)
 		return;
 
-	hci_conn_put(conn->parent);
-	conn->parent = NULL;
-
 	list_del_rcu(&conn->link->list);
 	synchronize_rcu();
 
+	hci_conn_put(conn->parent);
+	conn->parent = NULL;
+
 	kfree(conn->link);
 	conn->link = NULL;
 }
-- 
2.40.0

[PATCH v4 3/4] Bluetooth: Fix UAF in hci_conn_hash_flush again

[Ruihan Li]

Commit 06149746e720 ("Bluetooth: hci_conn: Add support for linking
multiple hcon") reintroduced a previously fixed bug [1] ("KASAN:
slab-use-after-free Read in hci_conn_hash_flush"). This bug was
originally fixed by commit 5dc7d23e167e ("Bluetooth: hci_conn: Fix
possible UAF").

The hci_conn_unlink function was added to avoid invalidating the link
traversal caused by successive hci_conn_del operations releasing extra
connections. However, currently hci_conn_unlink itself also releases
extra connections, resulted in the reintroduced bug.

This patch follows a more robust solution for cleaning up all
connections, by repeatedly removing the first connection until there are
none left. This approach does not rely on the inner workings of
hci_conn_del and ensures proper cleanup of all connections.

Meanwhile, we need to make sure that hci_conn_del never fails. Indeed it
doesn't, as it now always returns zero. To make this a bit clearer, this
patch also changes its return type to void.

Reported-by: syzbot+8bb72f86fc823817bc5d@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-bluetooth/000000000000aa920505f60d25ad@google.com/
Fixes: 06149746e720 ("Bluetooth: hci_conn: Add support for linking multiple hcon")
Signed-off-by: Ruihan Li <lrh2000@pku.edu.cn>
Co-developed-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
---
 include/net/bluetooth/hci_core.h |  2 +-
 net/bluetooth/hci_conn.c         | 33 +++++++++++++++++++++-----------
 2 files changed, 23 insertions(+), 12 deletions(-)

diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci_core.h
index a6c8aee2f..8baf34639 100644
--- a/include/net/bluetooth/hci_core.h
+++ b/include/net/bluetooth/hci_core.h
@@ -1327,7 +1327,7 @@ int hci_le_create_cis(struct hci_conn *conn);
 
 struct hci_conn *hci_conn_add(struct hci_dev *hdev, int type, bdaddr_t *dst,
 			      u8 role);
-int hci_conn_del(struct hci_conn *conn);
+void hci_conn_del(struct hci_conn *conn);
 void hci_conn_hash_flush(struct hci_dev *hdev);
 void hci_conn_check_pending(struct hci_dev *hdev);
 
diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index 44d0643fc..ce588359b 100644
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -1088,6 +1088,14 @@ static void hci_conn_unlink(struct hci_conn *conn)
 
 			hci_conn_unlink(child);
 
+			/* If hdev is down it means
+			 * hci_dev_close_sync/hci_conn_hash_flush is in progress
+			 * and links don't need to be cleanup as all connections
+			 * would be cleanup.
+			 */
+			if (!test_bit(HCI_UP, &hdev->flags))
+				continue;
+
 			/* Due to race, SCO connection might be not established
 			 * yet at this point. Delete it now, otherwise it is
 			 * possible for it to be stuck and can't be deleted.
@@ -1112,7 +1120,7 @@ static void hci_conn_unlink(struct hci_conn *conn)
 	conn->link = NULL;
 }
 
-int hci_conn_del(struct hci_conn *conn)
+void hci_conn_del(struct hci_conn *conn)
 {
 	struct hci_dev *hdev = conn->hdev;
 
@@ -1163,8 +1171,6 @@ int hci_conn_del(struct hci_conn *conn)
 	 * rest of hci_conn_del.
 	 */
 	hci_conn_cleanup(conn);
-
-	return 0;
 }
 
 struct hci_dev *hci_get_route(bdaddr_t *dst, bdaddr_t *src, uint8_t src_type)
@@ -2465,22 +2471,27 @@ void hci_conn_enter_active_mode(struct hci_conn *conn, __u8 force_active)
 /* Drop all connection on the device */
 void hci_conn_hash_flush(struct hci_dev *hdev)
 {
-	struct hci_conn_hash *h = &hdev->conn_hash;
-	struct hci_conn *c, *n;
+	struct list_head *head = &hdev->conn_hash.list;
+	struct hci_conn *conn;
 
 	BT_DBG("hdev %s", hdev->name);
 
-	list_for_each_entry_safe(c, n, &h->list, list) {
-		c->state = BT_CLOSED;
-
-		hci_disconn_cfm(c, HCI_ERROR_LOCAL_HOST_TERM);
+	/* We should not traverse the list here, because hci_conn_del
+	 * can remove extra links, which may cause the list traversal
+	 * to hit items that have already been released.
+	 */
+	while ((conn = list_first_entry_or_null(head,
+						struct hci_conn,
+						list)) != NULL) {
+		conn->state = BT_CLOSED;
+		hci_disconn_cfm(conn, HCI_ERROR_LOCAL_HOST_TERM);
 
 		/* Unlink before deleting otherwise it is possible that
 		 * hci_conn_del removes the link which may cause the list to
 		 * contain items already freed.
 		 */
-		hci_conn_unlink(c);
-		hci_conn_del(c);
+		hci_conn_unlink(conn);
+		hci_conn_del(conn);
 	}
 }
 
-- 
2.40.0

[PATCH v4 4/4] Bluetooth: Unlink CISes when LE disconnects in hci_conn_del

[Ruihan Li]

Currently, hci_conn_del calls hci_conn_unlink for BR/EDR, (e)SCO, and
CIS connections, i.e., everything except LE connections. However, if
(e)SCO connections are unlinked when BR/EDR disconnects, CIS connections
should also be unlinked when LE disconnects.

In terms of disconnection behavior, CIS and (e)SCO connections are not
too different. One peculiarity of CIS is that when CIS connections are
disconnected, the CIS handle isn't deleted, as per [BLUETOOTH CORE
SPECIFICATION Version 5.4 | Vol 4, Part E] 7.1.6 Disconnect command:

        All SCO, eSCO, and CIS connections on a physical link should be
        disconnected before the ACL connection on the same physical
        connection is disconnected. If it does not, they will be
        implicitly disconnected as part of the ACL disconnection.
        ...
        Note: As specified in Section 7.7.5, on the Central, the handle
        for a CIS remains valid even after disconnection and, therefore,
        the Host can recreate a disconnected CIS at a later point in
        time using the same connection handle.

Since hci_conn_link invokes both hci_conn_get and hci_conn_hold,
hci_conn_unlink should perform both hci_conn_put and hci_conn_drop as
well. However, currently it performs only hci_conn_put.

This patch makes hci_conn_unlink call hci_conn_drop as well, which
simplifies the logic in hci_conn_del a bit and may benefit future users
of hci_conn_unlink. But it is noted that this change additionally
implies that hci_conn_unlink can queue disc_work on conn itself, with
the following call stack:

        hci_conn_unlink(conn)  [conn->parent == NULL]
                -> hci_conn_unlink(child)  [child->parent == conn]
                        -> hci_conn_drop(child->parent)
                                -> queue_delayed_work(&conn->disc_work)

Queued disc_work after hci_conn_del can be spurious, so during the
process of hci_conn_del, it is necessary to make the call to
cancel_delayed_work(&conn->disc_work) after invoking hci_conn_unlink.

Signed-off-by: Ruihan Li <lrh2000@pku.edu.cn>
Co-developed-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
---
 net/bluetooth/hci_conn.c | 21 ++++++---------------
 1 file changed, 6 insertions(+), 15 deletions(-)

diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index ce588359b..f75ef12f1 100644
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -1100,7 +1100,9 @@ static void hci_conn_unlink(struct hci_conn *conn)
 			 * yet at this point. Delete it now, otherwise it is
 			 * possible for it to be stuck and can't be deleted.
 			 */
-			if (child->handle == HCI_CONN_HANDLE_UNSET)
+			if ((child->type == SCO_LINK ||
+			     child->type == ESCO_LINK) &&
+			    child->handle == HCI_CONN_HANDLE_UNSET)
 				hci_conn_del(child);
 		}
 
@@ -1113,6 +1115,7 @@ static void hci_conn_unlink(struct hci_conn *conn)
 	list_del_rcu(&conn->link->list);
 	synchronize_rcu();
 
+	hci_conn_drop(conn->parent);
 	hci_conn_put(conn->parent);
 	conn->parent = NULL;
 
@@ -1126,12 +1129,13 @@ void hci_conn_del(struct hci_conn *conn)
 
 	BT_DBG("%s hcon %p handle %d", hdev->name, conn, conn->handle);
 
+	hci_conn_unlink(conn);
+
 	cancel_delayed_work_sync(&conn->disc_work);
 	cancel_delayed_work_sync(&conn->auto_accept_work);
 	cancel_delayed_work_sync(&conn->idle_work);
 
 	if (conn->type == ACL_LINK) {
-		hci_conn_unlink(conn);
 		/* Unacked frames */
 		hdev->acl_cnt += conn->sent;
 	} else if (conn->type == LE_LINK) {
@@ -1142,13 +1146,6 @@ void hci_conn_del(struct hci_conn *conn)
 		else
 			hdev->acl_cnt += conn->sent;
 	} else {
-		struct hci_conn *acl = conn->parent;
-
-		if (acl) {
-			hci_conn_unlink(conn);
-			hci_conn_drop(acl);
-		}
-
 		/* Unacked ISO frames */
 		if (conn->type == ISO_LINK) {
 			if (hdev->iso_pkts)
@@ -2485,12 +2482,6 @@ void hci_conn_hash_flush(struct hci_dev *hdev)
 						list)) != NULL) {
 		conn->state = BT_CLOSED;
 		hci_disconn_cfm(conn, HCI_ERROR_LOCAL_HOST_TERM);
-
-		/* Unlink before deleting otherwise it is possible that
-		 * hci_conn_del removes the link which may cause the list to
-		 * contain items already freed.
-		 */
-		hci_conn_unlink(conn);
 		hci_conn_del(conn);
 	}
 }
-- 
2.40.0

RE: [v4,1/4] Bluetooth: Fix potential double free caused by hci_conn_unlink

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 6704 bytes --]

This is automated email and please do not reply to this email!

Dear submitter,

Thank you for submitting the patches to the linux bluetooth mailing list.
This is a CI test results with your patch series:
PW Link:https://patchwork.kernel.org/project/bluetooth/list/?series=744697

---Test result---

Test Summary:
CheckPatch                    FAIL      3.22 seconds
GitLint                       FAIL      1.40 seconds
SubjectPrefix                 PASS      0.28 seconds
BuildKernel                   PASS      43.05 seconds
CheckAllWarning               PASS      46.73 seconds
CheckSparse                   PASS      54.02 seconds
CheckSmatch                   PASS      143.56 seconds
BuildKernel32                 PASS      42.36 seconds
TestRunnerSetup               PASS      597.83 seconds
TestRunner_l2cap-tester       PASS      21.30 seconds
TestRunner_iso-tester         PASS      28.00 seconds
TestRunner_bnep-tester        PASS      7.24 seconds
TestRunner_mgmt-tester        PASS      146.36 seconds
TestRunner_rfcomm-tester      PASS      11.56 seconds
TestRunner_sco-tester         PASS      10.86 seconds
TestRunner_ioctl-tester       PASS      13.13 seconds
TestRunner_mesh-tester        PASS      9.28 seconds
TestRunner_smp-tester         PASS      10.50 seconds
TestRunner_userchan-tester    PASS      7.56 seconds
IncrementalBuild              PASS      88.80 seconds

Details
##############################
Test: CheckPatch - FAIL
Desc: Run checkpatch.pl script
Output:
[v4,1/4] Bluetooth: Fix potential double free caused by hci_conn_unlink
WARNING: Reported-by: should be immediately followed by Link: with a URL to the report
#82: 
Reported-by: syzbot+690b90b14f14f43f4688@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-bluetooth/000000000000484a8205faafe216@google.com/

WARNING: Possible unwrapped commit description (prefer a maximum 75 chars per line)
#83: 
Closes: https://lore.kernel.org/linux-bluetooth/000000000000484a8205faafe216@google.com/

WARNING: Unknown link reference 'Closes:', use 'Link:' instead
#83: 
Closes: https://lore.kernel.org/linux-bluetooth/000000000000484a8205faafe216@google.com/

total: 0 errors, 3 warnings, 0 checks, 33 lines checked

NOTE: For some of the reported defects, checkpatch may be able to
      mechanically convert to the typical style using --fix or --fix-inplace.

/github/workspace/src/src/13230190.patch has style problems, please review.

NOTE: Ignored message types: UNKNOWN_COMMIT_ID

NOTE: If any of the errors are false positives, please report
      them to the maintainer, see CHECKPATCH in MAINTAINERS.


[v4,2/4] Bluetooth: Refcnt drop must be placed last in hci_conn_unlink
WARNING: Reported-by: should be immediately followed by Link: with a URL to the report
#83: 
Reported-by: Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Closes: https://lore.kernel.org/linux-bluetooth/CABBYNZ+1kce8_RJrLNOXd_8=Mdpb=2bx4Nto-hFORk=qiOkoCg@mail.gmail.com/

WARNING: Possible unwrapped commit description (prefer a maximum 75 chars per line)
#84: 
Closes: https://lore.kernel.org/linux-bluetooth/CABBYNZ+1kce8_RJrLNOXd_8=Mdpb=2bx4Nto-hFORk=qiOkoCg@mail.gmail.com/

WARNING: Unknown link reference 'Closes:', use 'Link:' instead
#84: 
Closes: https://lore.kernel.org/linux-bluetooth/CABBYNZ+1kce8_RJrLNOXd_8=Mdpb=2bx4Nto-hFORk=qiOkoCg@mail.gmail.com/

total: 0 errors, 3 warnings, 0 checks, 15 lines checked

NOTE: For some of the reported defects, checkpatch may be able to
      mechanically convert to the typical style using --fix or --fix-inplace.

/github/workspace/src/src/13230188.patch has style problems, please review.

NOTE: Ignored message types: UNKNOWN_COMMIT_ID

NOTE: If any of the errors are false positives, please report
      them to the maintainer, see CHECKPATCH in MAINTAINERS.


[v4,3/4] Bluetooth: Fix UAF in hci_conn_hash_flush again
WARNING: Reported-by: should be immediately followed by Link: with a URL to the report
#94: 
Reported-by: syzbot+8bb72f86fc823817bc5d@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-bluetooth/000000000000aa920505f60d25ad@google.com/

WARNING: Possible unwrapped commit description (prefer a maximum 75 chars per line)
#95: 
Closes: https://lore.kernel.org/linux-bluetooth/000000000000aa920505f60d25ad@google.com/

WARNING: Unknown link reference 'Closes:', use 'Link:' instead
#95: 
Closes: https://lore.kernel.org/linux-bluetooth/000000000000aa920505f60d25ad@google.com/

total: 0 errors, 3 warnings, 0 checks, 73 lines checked

NOTE: For some of the reported defects, checkpatch may be able to
      mechanically convert to the typical style using --fix or --fix-inplace.

/github/workspace/src/src/13230191.patch has style problems, please review.

NOTE: Ignored message types: UNKNOWN_COMMIT_ID

NOTE: If any of the errors are false positives, please report
      them to the maintainer, see CHECKPATCH in MAINTAINERS.


##############################
Test: GitLint - FAIL
Desc: Run gitlint
Output:
[v4,1/4] Bluetooth: Fix potential double free caused by hci_conn_unlink

WARNING: I3 - ignore-body-lines: gitlint will be switching from using Python regex 'match' (match beginning) to 'search' (match anywhere) semantics. Please review your ignore-body-lines.regex option accordingly. To remove this warning, set general.regex-style-search=True. More details: https://jorisroovers.github.io/gitlint/configuration/#regex-style-search
13: B1 Line exceeds max length (88>80): "Closes: https://lore.kernel.org/linux-bluetooth/000000000000484a8205faafe216@google.com/"
[v4,2/4] Bluetooth: Refcnt drop must be placed last in hci_conn_unlink

WARNING: I3 - ignore-body-lines: gitlint will be switching from using Python regex 'match' (match beginning) to 'search' (match anywhere) semantics. Please review your ignore-body-lines.regex option accordingly. To remove this warning, set general.regex-style-search=True. More details: https://jorisroovers.github.io/gitlint/configuration/#regex-style-search
13: B1 Line exceeds max length (115>80): "Closes: https://lore.kernel.org/linux-bluetooth/CABBYNZ+1kce8_RJrLNOXd_8=Mdpb=2bx4Nto-hFORk=qiOkoCg@mail.gmail.com/"
[v4,3/4] Bluetooth: Fix UAF in hci_conn_hash_flush again

WARNING: I3 - ignore-body-lines: gitlint will be switching from using Python regex 'match' (match beginning) to 'search' (match anywhere) semantics. Please review your ignore-body-lines.regex option accordingly. To remove this warning, set general.regex-style-search=True. More details: https://jorisroovers.github.io/gitlint/configuration/#regex-style-search
24: B1 Line exceeds max length (88>80): "Closes: https://lore.kernel.org/linux-bluetooth/000000000000aa920505f60d25ad@google.com/"


---
Regards,
Linux Bluetooth

Re: [PATCH v4 1/4] Bluetooth: Fix potential double free caused by hci_conn_unlink

[patchwork-bot+bluetooth]

Hello:

This series was applied to bluetooth/bluetooth-next.git (master)
by Luiz Augusto von Dentz <luiz.von.dentz@intel.com>:

On Wed,  3 May 2023 21:39:34 +0800 you wrote:
> The hci_conn_unlink function is being called by hci_conn_del, which
> means it should not call hci_conn_del with the input parameter conn
> again. If it does, conn may have already been released when
> hci_conn_unlink returns, leading to potential UAF and double-free
> issues.
> 
> This patch resolves the problem by modifying hci_conn_unlink to release
> only conn's child links when necessary, but never release conn itself.
> 
> [...]

Here is the summary with links:
  - [v4,1/4] Bluetooth: Fix potential double free caused by hci_conn_unlink
    https://git.kernel.org/bluetooth/bluetooth-next/c/3214238e9dc7
  - [v4,2/4] Bluetooth: Refcnt drop must be placed last in hci_conn_unlink
    https://git.kernel.org/bluetooth/bluetooth-next/c/38e9b45310de
  - [v4,3/4] Bluetooth: Fix UAF in hci_conn_hash_flush again
    https://git.kernel.org/bluetooth/bluetooth-next/c/29f883dcbfd0
  - [v4,4/4] Bluetooth: Unlink CISes when LE disconnects in hci_conn_del
    https://git.kernel.org/bluetooth/bluetooth-next/c/e6e576ec4e72

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html