CVE-2024-53121

In the Linux kernel, the following vulnerability has been resolved:

net/mlx5: fs, lock FTE when checking if active

The referenced commits introduced a two-step process for deleting FTEs:

• Lock the FTE, delete it from hardware, set the hardware deletion function to NULL and unlock the FTE.
• Lock the parent flow group, delete the software copy of the FTE, and remove it from the xarray.

However, this approach encounters a race condition if a rule with the same match value is added simultaneously. In this scenario, fs_core may set the hardware deletion function to NULL prematurely, causing a panic during subsequent rule deletions.

To prevent this, ensure the active flag of the FTE is checked under a lock, which will prevent the fs_core layer from attaching a new steering rule to an FTE that is in the process of deletion.

[ 438.967589] MOSHE: 2496 mlx5_del_flow_rules del_hw_func [ 438.968205] ————[ cut here ]———— [ 438.968654] refcount_t: decrement hit 0; leaking memory. [ 438.969249] WARNING: CPU: 0 PID: 8957 at lib/refcount.c:31 refcount_warn_saturate+0xfb/0x110 [ 438.970054] Modules linked in: act_mirred cls_flower act_gact sch_ingress openvswitch nsh mlx5_vdpa vringh vhost_iotlb vdpa mlx5_ib mlx5_core xt_conntrack xt_MASQUERADE nf_conntrack_netlink nfnetlink xt_addrtype iptable_nat nf_nat br_netfilter rpcsec_gss_krb5 auth_rpcgss oid_registry overlay rpcrdma rdma_ucm ib_iser libiscsi scsi_transport_iscsi ib_umad rdma_cm ib_ipoib iw_cm ib_cm ib_uverbs ib_core zram zsmalloc fuse [last unloaded: cls_flower] [ 438.973288] CPU: 0 UID: 0 PID: 8957 Comm: tc Not tainted 6.12.0-rc1+ #8 [ 438.973888] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014 [ 438.974874] RIP: 0010:refcount_warn_saturate+0xfb/0x110 [ 438.975363] Code: 40 66 3b 82 c6 05 16 e9 4d 01 01 e8 1f 7c a0 ff 0f 0b c3 cc cc cc cc 48 c7 c7 10 66 3b 82 c6 05 fd e8 4d 01 01 e8 05 7c a0 ff <0f> 0b c3 cc cc cc cc 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 90 [ 438.976947] RSP: 0018:ffff888124a53610 EFLAGS: 00010286 [ 438.977446] RAX: 0000000000000000 RBX: ffff888119d56de0 RCX: 0000000000000000 [ 438.978090] RDX: ffff88852c828700 RSI: ffff88852c81b3c0 RDI: ffff88852c81b3c0 [ 438.978721] RBP: ffff888120fa0e88 R08: 0000000000000000 R09: ffff888124a534b0 [ 438.979353] R10: 0000000000000001 R11: 0000000000000001 R12: ffff888119d56de0 [ 438.979979] R13: ffff888120fa0ec0 R14: ffff888120fa0ee8 R15: ffff888119d56de0 [ 438.980607] FS: 00007fe6dcc0f800(0000) GS:ffff88852c800000(0000) knlGS:0000000000000000 [ 438.983984] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 438.984544] CR2: 00000000004275e0 CR3: 0000000186982001 CR4: 0000000000372eb0 [ 438.985205] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 438.985842] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 438.986507] Call Trace: [ 438.986799] [ 438.987070] ? __warn+0x7d/0x110 [ 438.987426] ? refcount_warn_saturate+0xfb/0x110 [ 438.987877] ? report_bug+0x17d/0x190 [ 438.988261] ? prb_read_valid+0x17/0x20 [ 438.988659] ? handle_bug+0x53/0x90 [ 438.989054] ? exc_invalid_op+0x14/0x70 [ 438.989458] ? asm_exc_invalid_op+0x16/0x20 [ 438.989883] ? refcount_warn_saturate+0xfb/0x110 [ 438.990348] mlx5_del_flow_rules+0x2f7/0x340 [mlx5_core] [ 438.990932] __mlx5_eswitch_del_rule+0x49/0x170 [mlx5_core] [ 438.991519] ? mlx5_lag_is_sriov+0x3c/0x50 [mlx5_core] [ 438.992054] ? xas_load+0x9/0xb0 [ 438.992407] mlx5e_tc_rule_unoffload+0x45/0xe0 [mlx5_core] [ 438.993037] mlx5e_tc_del_fdb_flow+0x2a6/0x2e0 [mlx5_core] [ 438.993623] mlx5e_flow_put+0x29/0x60 [mlx5_core] [ 438.994161] mlx5e_delete_flower+0x261/0x390 [mlx5_core] [ 438.994728] tc_setup_cb_destroy+0xb9/0x190 [ 438.995150] fl_hw_destroy_filter+0x94/0xc0 [cls_flower] [ 438.995650] fl_change+0x11a4/0x13c0 [cls_flower] [ 438.996105] tc_new_tfilter+0x347/0xbc0 [ 438.996503] ? __ —truncated—

Weakness

The product contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently.

Affected Software

Extended Description

This can have security implications when the expected synchronization is in security-critical code, such as recording whether a user is authenticated or modifying important state information that should not be influenced by an outsider. A race condition occurs within concurrent environments, and is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc. A race condition violates these properties, which are closely related:

A race condition exists when an “interfering code sequence” can still access the shared resource, violating exclusivity. Programmers may assume that certain code sequences execute too quickly to be affected by an interfering code sequence; when they are not, this violates atomicity. For example, the single “x++” statement may appear atomic at the code layer, but it is actually non-atomic at the instruction layer, since it involves a read (the original value of x), followed by a computation (x+1), followed by a write (save the result to x). The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.

Potential Mitigations

• Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring.
• Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/26.html
• https://cwe.mitre.org/data/definitions/29.html

References

• https://git.kernel.org/stable/c/094d1a2121cee1e85ab07d74388f94809dcfb5b9
• https://git.kernel.org/stable/c/0d568258f99f2076ab02e9234cbabbd43e12f30e
• https://git.kernel.org/stable/c/5b47c2f47c2fe921681f4a4fe2790375e6c04cdd
• https://git.kernel.org/stable/c/933ef0d17f012b653e9e6006e3f50c8d0238b5ed
• https://git.kernel.org/stable/c/9ca314419930f9135727e39d77e66262d5f7bef6
• https://git.kernel.org/stable/c/a508c74ceae2f5a4647f67c362126516d6404ed9
• https://git.kernel.org/stable/c/bfba288f53192db08c68d4c568db9783fb9cb838