[PATCH] Bluetooth: hci_sync: fix stack buffer overflow in hci_le_big_create_sync

[PATCH] Bluetooth: hci_sync: fix stack buffer overflow in hci_le_big_create_sync

[hkbinbin]

hci_le_big_create_sync() uses DEFINE_FLEX to allocate a
struct hci_cp_le_big_create_sync on the stack with room for 0x11 (17)
BIS entries.  However, conn->num_bis can hold up to HCI_MAX_ISO_BIS (31)
entries — validated against ISO_MAX_NUM_BIS (0x1f) in the caller
hci_conn_big_create_sync().  When conn->num_bis is between 18 and 31,
the memcpy that copies conn->bis into cp->bis writes up to 14 bytes
past the stack buffer, corrupting adjacent stack memory.

This is trivially reproducible: binding an ISO socket with
bc_num_bis = ISO_MAX_NUM_BIS (31) and calling listen() will
eventually trigger hci_le_big_create_sync() from the HCI command
sync worker, causing a KASAN-detectable stack-out-of-bounds write:

  BUG: KASAN: stack-out-of-bounds in hci_le_big_create_sync+0x256/0x3b0
  Write of size 31 at addr ffffc90000487b48 by task kworker/u9:0/71

Fix this by changing the DEFINE_FLEX count from the incorrect 0x11 to
HCI_MAX_ISO_BIS, which matches the maximum number of BIS entries that
conn->bis can actually carry.

Fixes: 42ecf1947135 ("Bluetooth: ISO: Do not emit LE BIG Create Sync if previous is pending")
Cc: stable@vger.kernel.org
Signed-off-by: hkbinbin <hkbinbinbin@gmail.com>
---
 net/bluetooth/hci_sync.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
index 45d16639874a..b84587061ae0 100644
--- a/net/bluetooth/hci_sync.c
+++ b/net/bluetooth/hci_sync.c
@@ -7222,7 +7222,8 @@ static void create_big_complete(struct hci_dev *hdev, void *data, int err)
 
 static int hci_le_big_create_sync(struct hci_dev *hdev, void *data)
 {
-	DEFINE_FLEX(struct hci_cp_le_big_create_sync, cp, bis, num_bis, 0x11);
+	DEFINE_FLEX(struct hci_cp_le_big_create_sync, cp, bis, num_bis,
+		    HCI_MAX_ISO_BIS);
 	struct hci_conn *conn = data;
 	struct bt_iso_qos *qos = &conn->iso_qos;
 	int err;
-- 
2.51.0

Re: [PATCH] Bluetooth: hci_sync: fix stack buffer overflow in hci_le_big_create_sync

[Paul Menzel]

Dear hkbinbin,


Thank you for your patch. It’d be great if you spelt your name with 
capital letters and spaces (`git config --global user.name "…"`).

Am 31.03.26 um 07:39 schrieb hkbinbin:
> hci_le_big_create_sync() uses DEFINE_FLEX to allocate a
> struct hci_cp_le_big_create_sync on the stack with room for 0x11 (17)
> BIS entries.  However, conn->num_bis can hold up to HCI_MAX_ISO_BIS (31)
> entries — validated against ISO_MAX_NUM_BIS (0x1f) in the caller
> hci_conn_big_create_sync().  When conn->num_bis is between 18 and 31,
> the memcpy that copies conn->bis into cp->bis writes up to 14 bytes
> past the stack buffer, corrupting adjacent stack memory.
> 
> This is trivially reproducible: binding an ISO socket with
> bc_num_bis = ISO_MAX_NUM_BIS (31) and calling listen() will

If this is not more than twenty lines, maybe share the program/script?

> eventually trigger hci_le_big_create_sync() from the HCI command
> sync worker, causing a KASAN-detectable stack-out-of-bounds write:
> 
>    BUG: KASAN: stack-out-of-bounds in hci_le_big_create_sync+0x256/0x3b0
>    Write of size 31 at addr ffffc90000487b48 by task kworker/u9:0/71
> 
> Fix this by changing the DEFINE_FLEX count from the incorrect 0x11 to
> HCI_MAX_ISO_BIS, which matches the maximum number of BIS entries that
> conn->bis can actually carry.
> 
> Fixes: 42ecf1947135 ("Bluetooth: ISO: Do not emit LE BIG Create Sync if previous is pending")

Just for the record, that the commit is present since Linux v6.13-rc1.

> Cc: stable@vger.kernel.org
> Signed-off-by: hkbinbin <hkbinbinbin@gmail.com>
> ---
>   net/bluetooth/hci_sync.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
> index 45d16639874a..b84587061ae0 100644
> --- a/net/bluetooth/hci_sync.c
> +++ b/net/bluetooth/hci_sync.c
> @@ -7222,7 +7222,8 @@ static void create_big_complete(struct hci_dev *hdev, void *data, int err)
>   
>   static int hci_le_big_create_sync(struct hci_dev *hdev, void *data)
>   {
> -	DEFINE_FLEX(struct hci_cp_le_big_create_sync, cp, bis, num_bis, 0x11);
> +	DEFINE_FLEX(struct hci_cp_le_big_create_sync, cp, bis, num_bis,
> +		    HCI_MAX_ISO_BIS);
>   	struct hci_conn *conn = data;
>   	struct bt_iso_qos *qos = &conn->iso_qos;
>   	int err;

The diff looks good. Great find.

Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>


Kind regards,

Paul

RE: Bluetooth: hci_sync: fix stack buffer overflow in hci_le_big_create_sync

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 2593 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=1074953

---Test result---

Test Summary:
CheckPatch                    PENDING   0.28 seconds
GitLint                       PENDING   0.25 seconds
SubjectPrefix                 PASS      0.12 seconds
BuildKernel                   PASS      26.85 seconds
CheckAllWarning               PASS      29.24 seconds
CheckSparse                   PASS      27.93 seconds
BuildKernel32                 PASS      25.87 seconds
TestRunnerSetup               PASS      577.11 seconds
TestRunner_l2cap-tester       PASS      28.50 seconds
TestRunner_iso-tester         PASS      43.01 seconds
TestRunner_bnep-tester        PASS      6.46 seconds
TestRunner_mgmt-tester        FAIL      114.42 seconds
TestRunner_rfcomm-tester      PASS      9.60 seconds
TestRunner_sco-tester         FAIL      14.70 seconds
TestRunner_ioctl-tester       PASS      10.69 seconds
TestRunner_mesh-tester        FAIL      12.45 seconds
TestRunner_smp-tester         PASS      8.84 seconds
TestRunner_userchan-tester    PASS      6.81 seconds
IncrementalBuild              PENDING   0.65 seconds

Details
##############################
Test: CheckPatch - PENDING
Desc: Run checkpatch.pl script
Output:

##############################
Test: GitLint - PENDING
Desc: Run gitlint
Output:

##############################
Test: TestRunner_mgmt-tester - FAIL
Desc: Run mgmt-tester with test-runner
Output:
Total: 494, Passed: 489 (99.0%), Failed: 1, Not Run: 4

Failed Test Cases
Read Exp Feature - Success                           Failed       0.109 seconds
##############################
Test: TestRunner_sco-tester - FAIL
Desc: Run sco-tester with test-runner
Output:
WARNING: possible circular locking dependency detected
BUG: sleeping function called from invalid context at net/core/sock.c:3782
Total: 30, Passed: 30 (100.0%), Failed: 0, Not Run: 0
##############################
Test: TestRunner_mesh-tester - FAIL
Desc: Run mesh-tester with test-runner
Output:
Total: 10, Passed: 8 (80.0%), Failed: 2, Not Run: 0

Failed Test Cases
Mesh - Send cancel - 1                               Timed out    2.719 seconds
Mesh - Send cancel - 2                               Timed out    1.995 seconds
##############################
Test: IncrementalBuild - PENDING
Desc: Incremental build with the patches in the series
Output:



---
Regards,
Linux Bluetooth

Re: [PATCH] Bluetooth: hci_sync: fix stack buffer overflow in hci_le_big_create_sync

[patchwork-bot+bluetooth]

Hello:

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

On Tue, 31 Mar 2026 05:39:16 +0000 you wrote:
> hci_le_big_create_sync() uses DEFINE_FLEX to allocate a
> struct hci_cp_le_big_create_sync on the stack with room for 0x11 (17)
> BIS entries.  However, conn->num_bis can hold up to HCI_MAX_ISO_BIS (31)
> entries — validated against ISO_MAX_NUM_BIS (0x1f) in the caller
> hci_conn_big_create_sync().  When conn->num_bis is between 18 and 31,
> the memcpy that copies conn->bis into cp->bis writes up to 14 bytes
> past the stack buffer, corrupting adjacent stack memory.
> 
> [...]

Here is the summary with links:
  - Bluetooth: hci_sync: fix stack buffer overflow in hci_le_big_create_sync
    https://git.kernel.org/bluetooth/bluetooth-next/c/4797dfba1aa5

You are awesome, thank you!
-- 
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