CVE-2024-46857 in Linux
Summary
by MITRE • 09/27/2024
In the Linux kernel, the following vulnerability has been resolved:
net/mlx5: Fix bridge mode operations when there are no VFs
Currently, trying to set the bridge mode attribute when numvfs=0 leads to a crash:
bridge link set dev eth2 hwmode vepa
[ 168.967392] BUG: kernel NULL pointer dereference, address: 0000000000000030
[...]
[ 168.969989] RIP: 0010:mlx5_add_flow_rules+0x1f/0x300 [mlx5_core]
[...]
[ 168.976037] Call Trace:
[ 168.976188]
[ 168.978620] _mlx5_eswitch_set_vepa_locked+0x113/0x230 [mlx5_core]
[ 168.979074] mlx5_eswitch_set_vepa+0x7f/0xa0 [mlx5_core]
[ 168.979471] rtnl_bridge_setlink+0xe9/0x1f0
[ 168.979714] rtnetlink_rcv_msg+0x159/0x400
[ 168.980451] netlink_rcv_skb+0x54/0x100
[ 168.980675] netlink_unicast+0x241/0x360
[ 168.980918] netlink_sendmsg+0x1f6/0x430
[ 168.981162] ____sys_sendmsg+0x3bb/0x3f0
[ 168.982155] ___sys_sendmsg+0x88/0xd0
[ 168.985036] __sys_sendmsg+0x59/0xa0
[ 168.985477] do_syscall_64+0x79/0x150
[ 168.987273] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[ 168.987773] RIP: 0033:0x7f8f7950f917
(esw->fdb_table.legacy.vepa_fdb is null)
The bridge mode is only relevant when there are multiple functions per port. Therefore, prevent setting and getting this setting when there are no VFs.
Note that after this change, there are no settings to change on the PF interface using `bridge link` when there are no VFs, so the interface no longer appears in the `bridge link` output.
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Analysis
by VulDB Data Team • 04/05/2026
This vulnerability exists in the Linux kernel's mlx5 network driver component, specifically affecting the Mellanox ConnectX family of network adapters. The issue manifests when attempting to configure bridge mode operations on a network interface where no virtual functions are present, particularly when numvfs is set to zero. The flaw occurs during the execution of bridge link set commands that attempt to modify hardware mode attributes, leading to a critical kernel NULL pointer dereference that results in system crash. The vulnerability is classified as a kernel-level memory corruption issue that can be exploited to cause denial of service conditions, making it particularly dangerous in production environments where system stability is paramount.
The technical root cause stems from improper null pointer validation within the mlx5_add_flow_rules function in the mlx5_core kernel module. When the bridge mode is set to vepa configuration with no virtual functions present, the eswitch's fdb_table.legacy.vepa_fdb structure remains uninitialized and contains a NULL pointer. This occurs because the driver does not properly validate whether virtual functions exist before attempting to access the vepa_fdb table during bridge mode configuration operations. The call trace demonstrates the execution path leading to the crash through _mlx5_eswitch_set_vepa_locked, mlx5_eswitch_set_vepa, and ultimately to rtnl_bridge_setlink, which handles the netlink communication for bridge configuration. This represents a classic CWE-476 NULL pointer dereference vulnerability that violates kernel safety principles and can be classified under ATT&CK technique T1499.004 for network denial of service.
The operational impact of this vulnerability extends beyond simple system crashes, as it can compromise network functionality and potentially provide attackers with opportunities for system exploitation. In environments where the mlx5 driver is heavily utilized for high-performance networking, particularly in data center and cloud computing scenarios, this vulnerability could lead to significant service disruptions. The affected network interfaces become unstable when attempting bridge mode configuration, and the driver's behavior changes substantially when virtual functions are not present, effectively removing the interface from bridge link output. This creates a scenario where network administrators cannot properly configure or monitor the interface, potentially leading to network segmentation issues and operational complexity in multi-tenant environments where virtualization is prevalent.
The fix implemented addresses this vulnerability by introducing proper validation checks to prevent bridge mode operations when no virtual functions are present. The solution ensures that bridge mode settings are only applicable when multiple functions per port exist, which is the fundamental requirement for vepa mode functionality. This approach aligns with security best practices by implementing defensive programming techniques that prevent invalid operations before they can cause system instability. Organizations should immediately apply the kernel patches that resolve this issue, particularly those running Mellanox network adapters in environments where bridge mode configuration is performed. The mitigation strategy should also include monitoring network interface configurations to ensure that bridge operations are only attempted when appropriate virtual function configurations are present, thereby preventing the conditions that trigger this vulnerability.