CVE-2023-53591 in Linux
Summary
by MITRE • 10/04/2025
In the Linux kernel, the following vulnerability has been resolved:
net/mlx5e: Fix deadlock in tc route query code
Cited commit causes ABBA deadlock[0] when peer flows are created while
holding the devcom rw semaphore. Due to peer flows offload implementation the lock is taken much higher up the call chain and there is no obvious way to easily fix the deadlock. Instead, since tc route query code needs the peer eswitch structure only to perform a lookup in xarray and doesn't perform any sleeping operations with it, refactor the code for lockless execution in following ways:
- RCUify the devcom 'data' pointer. When resetting the pointer synchronously wait for RCU grace period before returning. This is fine since devcom is currently only used for synchronization of pairing/unpairing of eswitches which is rare and already expensive as-is.
- Wrap all usages of 'paired' boolean in {READ|WRITE}_ONCE(). The flag has
already been used in some unlocked contexts without proper annotations (e.g. users of mlx5_devcom_is_paired() function), but it wasn't an issue since all relevant code paths checked it again after obtaining the devcom semaphore. Now it is also used by mlx5_devcom_get_peer_data_rcu() as "best effort" check to return NULL when devcom is being unpaired. Note that while RCU read lock doesn't prevent the unpaired flag from being changed concurrently it still guarantees that reader can continue to use 'data'.
- Refactor mlx5e_tc_query_route_vport() function to use new mlx5_devcom_get_peer_data_rcu() API which fixes the deadlock.
[0]:
[ 164.599612] ======================================================
[ 164.600142] WARNING: possible circular locking dependency detected
[ 164.600667] 6.3.0-rc3+ #1 Not tainted
[ 164.601021] ------------------------------------------------------
[ 164.601557] handler1/3456 is trying to acquire lock:
[ 164.601998] ffff88811f1714b0 (&esw->offloads.encap_tbl_lock){+.+.}-{3:3}, at: mlx5e_attach_encap+0xd8/0x8b0 [mlx5_core]
[ 164.603078]
but task is already holding lock: [ 164.603617] ffff88810137fc98 (&comp->sem){++++}-{3:3}, at: mlx5_devcom_get_peer_data+0x37/0x80 [mlx5_core]
[ 164.604459]
which lock already depends on the new lock.
[ 164.605190]
the existing dependency chain (in reverse order) is: [ 164.605848]
-> #1 (&comp->sem){++++}-{3:3}:
[ 164.606380] down_read+0x39/0x50
[ 164.606772] mlx5_devcom_get_peer_data+0x37/0x80 [mlx5_core]
[ 164.607336] mlx5e_tc_query_route_vport+0x86/0xc0 [mlx5_core]
[ 164.607914] mlx5e_tc_tun_route_lookup+0x1a4/0x1d0 [mlx5_core]
[ 164.608495] mlx5e_attach_decap_route+0xc6/0x1e0 [mlx5_core]
[ 164.609063] mlx5e_tc_add_fdb_flow+0x1ea/0x360 [mlx5_core]
[ 164.609627] __mlx5e_add_fdb_flow+0x2d2/0x430 [mlx5_core]
[ 164.610175] mlx5e_configure_flower+0x952/0x1a20 [mlx5_core]
[ 164.610741] tc_setup_cb_add+0xd4/0x200
[ 164.611146] fl_hw_replace_filter+0x14c/0x1f0 [cls_flower]
[ 164.611661] fl_change+0xc95/0x18a0 [cls_flower]
[ 164.612116] tc_new_tfilter+0x3fc/0xd20
[ 164.612516] rtnetlink_rcv_msg+0x418/0x5b0
[ 164.612936] netlink_rcv_skb+0x54/0x100
[ 164.613339] netlink_unicast+0x190/0x250
[ 164.613746] netlink_sendmsg+0x245/0x4a0
[ 164.614150] sock_sendmsg+0x38/0x60
[ 164.614522] ____sys_sendmsg+0x1d0/0x1e0
[ 164.614934] ___sys_sendmsg+0x80/0xc0
[ 164.615320] __sys_sendmsg+0x51/0x90
[ 164.615701] do_syscall_64+0x3d/0x90
[ 164.616083] entry_SYSCALL_64_after_hwframe+0x46/0xb0
[ 164.616568]
-> #0 (&esw->offloads.encap_tbl_lock){+.+.}-{3:3}:
[ 164.617210] __lock_acquire+0x159e/0x26e0
[ 164.617638] lock_acquire+0xc2/0x2a0
[ 164.618018] __mutex_lock+0x92/0xcd0
[ 164.618401] mlx5e_attach_encap+0xd8/0x8b0 [mlx5_core]
[ 164.618943] post_process_attr+0x153/0x2d0 [
---truncated---
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Analysis
by VulDB Data Team • 04/27/2026
The vulnerability identified as CVE-2023-53591 resides within the Linux kernel's mlx5e network driver, specifically affecting the mlx5 core module responsible for managing Mellanox ConnectX network adapters. This issue manifests as an ABBA deadlock condition that occurs during the processing of traffic control (tc) route queries, particularly when peer flows are being created while holding the devcom read-write semaphore. The deadlock arises from a circular dependency between locks, where the system attempts to acquire the encap_tbl_lock while already holding the devcom semaphore, creating a scenario that prevents further execution and ultimately leads to system hang or crash. The root cause stems from the interaction between the peer flows offload implementation and the tc route query code, which requires access to the peer eswitch structure for lookup operations without performing any sleeping operations that would require exclusive lock access.
The technical flaw involves a classic deadlock pattern where lock ordering dependencies are violated due to the hierarchical nature of lock acquisition in the driver's code path. The mlx5e_tc_query_route_vport function attempts to access peer data structures while already holding the devcom semaphore, which is subsequently required by peer flow creation operations that need to acquire the encap_tbl_lock. This creates a situation where thread A holds the devcom semaphore and waits for encap_tbl_lock while thread B holds the encap_tbl_lock and waits for devcom semaphore, resulting in a circular dependency that cannot be resolved without external intervention. The issue is particularly problematic in high-throughput networking environments where tc route queries and peer flow creation occur concurrently, as it can lead to complete system unresponsiveness.
The operational impact of this vulnerability is significant for systems utilizing Mellanox network adapters with advanced offloading features, particularly in data center and high-performance computing environments where traffic control policies are actively applied. The deadlock condition can cause complete system hangs, requiring manual intervention or system reboot to restore functionality. This affects network reliability and availability, potentially leading to service disruption in production environments. The vulnerability is especially concerning for virtualized environments where peer flows are frequently created and managed, as the locking contention increases with the complexity of network topologies and the number of virtual machines sharing the same physical network adapter.
The mitigation strategy implemented in the fix involves refactoring the code to enable lockless execution through RCU (Read-Copy-Update) mechanisms and proper atomic operations. The devcom 'data' pointer is made RCU-protected, ensuring that when the pointer is reset, the system waits for an RCU grace period before returning, which is acceptable given that devcom pairing/unpairing operations are infrequent and already resource-intensive. The 'paired' boolean flag is wrapped with READ_ONCE and WRITE_ONCE macros to ensure proper memory ordering and prevent race conditions in unlocked contexts. Most importantly, the mlx5e_tc_query_route_vport function is refactored to utilize the new mlx5_devcom_get_peer_data_rcu() API, which eliminates the need to hold the devcom semaphore during peer data access, thereby breaking the circular dependency. This approach aligns with the ATT&CK framework's concept of privilege escalation through kernel-level vulnerabilities and follows CWE guidelines for preventing deadlock conditions in concurrent systems by using lock-free data structures and proper synchronization primitives. The fix demonstrates a best practice in kernel security by addressing the root cause rather than merely patching symptoms, ensuring that the tc route query functionality can operate without blocking the peer flow creation mechanisms that depend on the same lock hierarchy.