bpf: Fix RCU stall in bpf_fd_array_map_clear()

Overview

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

bpf: Fix RCU stall in bpf_fd_array_map_clear()

Add a missing cond_resched() in bpf_fd_array_map_clear() loop.

For PROG_ARRAY maps with many entries this loop calls prog_array_map_poke_run() per entry which can be expensive, and without yielding this can cause RCU stalls under load:

rcu: Stack dump where RCU GP kthread last ran: CPU: 0 UID: 0 PID: 30932 Comm: kworker/0:2 Not tainted 6.14.0-13195-g967e8def1100 #2 PREEMPT(undef) Workqueue: events prog_array_map_clear_deferred RIP: 0010:write_comp_data+0x38/0x90 kernel/kcov.c:246 Call Trace: <TASK> prog_array_map_poke_run+0x77/0x380 kernel/bpf/arraymap.c:1096 __fd_array_map_delete_elem+0x197/0x310 kernel/bpf/arraymap.c:925 bpf_fd_array_map_clear kernel/bpf/arraymap.c:1000 [inline] prog_array_map_clear_deferred+0x119/0x1b0 kernel/bpf/arraymap.c:1141 process_one_work+0x898/0x19d0 kernel/workqueue.c:3238 process_scheduled_works kernel/workqueue.c:3319 [inline] worker_thread+0x770/0x10b0 kernel/workqueue.c:3400 kthread+0x465/0x880 kernel/kthread.c:464 ret_from_fork+0x4d/0x80 arch/x86/kernel/process.c:153 ret_from_fork_asm+0x19/0x30 arch/x86/entry/entry_64.S:245 </TASK>

Affected

• Linux >= da765a2f599304a81a25e77908d1790414ecdbb6 < 419878a48085e6d5c2fcc4912eeaac2f8abf36ed
• Linux >= da765a2f599304a81a25e77908d1790414ecdbb6 < b1f7158a86f3cbac4d5a32beb55ca0f8027d44cd
• Linux >= da765a2f599304a81a25e77908d1790414ecdbb6 < 71ddb7defc442ab38c53123c384fedbfd8410a15
• Linux >= da765a2f599304a81a25e77908d1790414ecdbb6 < e1ed678855e315f90c70c1723e94157a9a82e660
• Linux >= da765a2f599304a81a25e77908d1790414ecdbb6 < 67bdb4b0d26f2d6bbf1798a925ef5a3b9ed7357a
• Linux >= da765a2f599304a81a25e77908d1790414ecdbb6 < 4406942e65ca128c56c67443832988873c21d2e9
• Linux 5.5

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.