Bug 2404109 (CVE-2025-39979)

Summary: CVE-2025-39979 kernel: net/mlx5: fs, fix UAF in flow counter release
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Version: unspecifiedKeywords: Security
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OS: Linux   
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A use-after-free flaw was discovered in the Linux kernel’s mlx5 (Net/MLX5) subsystem: within the function mlx5_cmd_hws_delete_fte() the HWS action reference count and mutex for a local flow counter were not initialized, meaning the flow-counter structure could already be freed while deleting the rule. This may lead to memory corruption or kernel instability.
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Description OSIDB Bzimport 2025-10-15 08:02:33 UTC 
In the Linux kernel, the following vulnerability has been resolved:

net/mlx5: fs, fix UAF in flow counter release

Fix a kernel trace [1] caused by releasing an HWS action of a local flow
counter in mlx5_cmd_hws_delete_fte(), where the HWS action refcount and
mutex were not initialized and the counter struct could already be freed
when deleting the rule.

Fix it by adding the missing initializations and adding refcount for the
local flow counter struct.

[1] Kernel log:
 Call Trace:
  <TASK>
  dump_stack_lvl+0x34/0x48
  mlx5_fs_put_hws_action.part.0.cold+0x21/0x94 [mlx5_core]
  mlx5_fc_put_hws_action+0x96/0xad [mlx5_core]
  mlx5_fs_destroy_fs_actions+0x8b/0x152 [mlx5_core]
  mlx5_cmd_hws_delete_fte+0x5a/0xa0 [mlx5_core]
  del_hw_fte+0x1ce/0x260 [mlx5_core]
  mlx5_del_flow_rules+0x12d/0x240 [mlx5_core]
  ? ttwu_queue_wakelist+0xf4/0x110
  mlx5_ib_destroy_flow+0x103/0x1b0 [mlx5_ib]
  uverbs_free_flow+0x20/0x50 [ib_uverbs]
  destroy_hw_idr_uobject+0x1b/0x50 [ib_uverbs]
  uverbs_destroy_uobject+0x34/0x1a0 [ib_uverbs]
  uobj_destroy+0x3c/0x80 [ib_uverbs]
  ib_uverbs_run_method+0x23e/0x360 [ib_uverbs]
  ? uverbs_finalize_object+0x60/0x60 [ib_uverbs]
  ib_uverbs_cmd_verbs+0x14f/0x2c0 [ib_uverbs]
  ? do_tty_write+0x1a9/0x270
  ? file_tty_write.constprop.0+0x98/0xc0
  ? new_sync_write+0xfc/0x190
  ib_uverbs_ioctl+0xd7/0x160 [ib_uverbs]
  __x64_sys_ioctl+0x87/0xc0
  do_syscall_64+0x59/0x90
Comment 1 Alexander B 2025-10-16 10:56:59 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025101559-CVE-2025-39979-f1e9@gregkh/T
Comment 7 errata-xmlrpc 2025-12-08 14:42:33 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 10

Via RHSA-2025:22854 https://access.redhat.com/errata/RHSA-2025:22854
Comment 8 errata-xmlrpc 2025-12-08 17:59:37 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9

Via RHSA-2025:22865 https://access.redhat.com/errata/RHSA-2025:22865