Overview
CVE-2025-40250 addresses a vulnerability in the Linux kernel’s `mlx5` driver, specifically related to interrupt request (IRQ) allocation. When the system fails to allocate an IRQ vector during the `mlx5_irq_alloc()` function, improper cleanup could lead to the freeing of the entire rmap (resource map), resulting in a kernel crash. This issue is observed when both `fwctl` and `rds` configurations are enabled.
Technical Details
The root cause of the vulnerability lies in the incorrect cleanup procedure executed after a failed `request_irq()` call within the `mlx5_irq_alloc()` function. Instead of only removing the newly added (and failed) IRQ mapping, the entire rmap was inadvertently freed. Subsequent attempts by other threads to access this freed memory resulted in a general protection fault and a system crash.
The fix implemented in the kernel addresses this by modifying the cleanup process to remove only the specific IRQ mapping that was being added when the `request_irq()` call failed. This targeted cleanup ensures that other valid mappings are not affected, preventing the crash.
The following call trace illustrates the potential crash scenario:
mlx5_core 0000:05:00.0: Successfully registered panic handler for port 1
mlx5_core 0000:05:00.0: mlx5_irq_alloc:293:(pid 66740): Failed to
request irq. err = -28
infiniband mlx5_0: mlx5_ib_test_wc:290:(pid 66740): Error -28 while
trying to test write-combining support
mlx5_core 0000:05:00.0: Successfully unregistered panic handler for port 1
mlx5_core 0000:06:00.0: Successfully registered panic handler for port 1
mlx5_core 0000:06:00.0: mlx5_irq_alloc:293:(pid 66740): Failed to
request irq. err = -28
infiniband mlx5_0: mlx5_ib_test_wc:290:(pid 66740): Error -28 while
trying to test write-combining support
mlx5_core 0000:06:00.0: Successfully unregistered panic handler for port 1
mlx5_core 0000:03:00.0: mlx5_irq_alloc:293:(pid 28895): Failed to
request irq. err = -28
mlx5_core 0000:05:00.0: mlx5_irq_alloc:293:(pid 28895): Failed to
request irq. err = -28
general protection fault, probably for non-canonical address
0xe277a58fde16f291: 0000 [#1] SMP NOPTI
RIP: 0010:free_irq_cpu_rmap+0x23/0x7d
Call Trace:
<TASK>
? show_trace_log_lvl+0x1d6/0x2f9
? show_trace_log_lvl+0x1d6/0x2f9
? mlx5_irq_alloc.cold+0x5d/0xf3 [mlx5_core]
? __die_body.cold+0x8/0xa
? die_addr+0x39/0x53
? exc_general_protection+0x1c4/0x3e9
? dev_vprintk_emit+0x5f/0x90
? asm_exc_general_protection+0x22/0x27
? free_irq_cpu_rmap+0x23/0x7d
mlx5_irq_alloc.cold+0x5d/0xf3 [mlx5_core]
irq_pool_request_vector+0x7d/0x90 [mlx5_core]
mlx5_irq_request+0x2e/0xe0 [mlx5_core]
mlx5_irq_request_vector+0xad/0xf7 [mlx5_core]
comp_irq_request_pci+0x64/0xf0 [mlx5_core]
create_comp_eq+0x71/0x385 [mlx5_core]
? mlx5e_open_xdpsq+0x11c/0x230 [mlx5_core]
mlx5_comp_eqn_get+0x72/0x90 [mlx5_core]
? xas_load+0x8/0x91
mlx5_comp_irqn_get+0x40/0x90 [mlx5_core]
mlx5e_open_channel+0x7d/0x3c7 [mlx5_core]
mlx5e_open_channels+0xad/0x250 [mlx5_core]
mlx5e_open_locked+0x3e/0x110 [mlx5_core]
mlx5e_open+0x23/0x70 [mlx5_core]
__dev_open+0xf1/0x1a5
__dev_change_flags+0x1e1/0x249
dev_change_flags+0x21/0x5c
do_setlink+0x28b/0xcc4
? __nla_parse+0x22/0x3d
? inet6_validate_link_af+0x6b/0x108
? cpumask_next+0x1f/0x35
? __snmp6_fill_stats64.constprop.0+0x66/0x107
? __nla_validate_parse+0x48/0x1e6
__rtnl_newlink+0x5ff/0xa57
? kmem_cache_alloc_trace+0x164/0x2ce
rtnl_newlink+0x44/0x6e
rtnetlink_rcv_msg+0x2bb/0x362
? __netlink_sendskb+0x4c/0x6c
? netlink_unicast+0x28f/0x2ce
? rtnl_calcit.isra.0+0x150/0x146
netlink_rcv_skb+0x5f/0x112
netlink_unicast+0x213/0x2ce
netlink_sendmsg+0x24f/0x4d9
__sock_sendmsg+0x65/0x6a
____sys_sendmsg+0x28f/0x2c9
? import_iovec+0x17/0x2b
___sys_sendmsg+0x97/0xe0
__sys_sendmsg+0x81/0xd8
do_syscall_64+0x35/0x87
entry_SYSCALL_64_after_hwframe+0x6e/0x0
RIP: 0033:0x7fc328603727
Code: c3 66 90 41 54 41 89 d4 55 48 89 f5 53 89 fb 48 83 ec 10 e8 0b ed
ff ff 44 89 e2 48 89 ee 89 df 41 89 c0 b8 2e 00 00 00 0f 05 <48> 3d 00
f0 ff ff 77 35 44 89 c7 48 89 44 24 08 e8 44 ed ff ff 48
RSP: 002b:00007ffe8eb3f1a0 EFLAGS: 00000293 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 000000000000000d RCX: 00007fc328603727
RDX: 0000000000000000 RSI: 00007ffe8eb3f1f0 RDI: 000000000000000d
RBP: 00007ffe8eb3f1f0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000000
R13: 00000000000
---truncated---
CVSS Analysis
Due to the potential for a kernel crash leading to a denial of service, this vulnerability is considered to have a high impact. However, a specific CVSS score has not been assigned at this time. Factors influencing the severity include the requirement for specific configurations (`fwctl` and `rds` enabled) to trigger the vulnerability and the reliance on the system exhausting IRQ vectors.
Possible Impact
The primary impact of CVE-2025-40250 is a denial-of-service condition resulting from a kernel crash. This can lead to:
- System unavailability
- Data loss (if the system is in the process of writing data to disk)
- Interruption of critical services
Mitigation and Patch Steps
The vulnerability is resolved by applying the patch provided by the Linux kernel developers. Users are strongly advised to update their kernels to a version containing the fix. The specific commits addressing this issue are listed in the References section below.
To mitigate the risk before applying the patch, consider the following:
- Reducing the number of devices or services that require IRQ allocation may lower the chance of exhausting IRQ vectors, though this may impact functionality.
- Monitoring system logs for warnings related to IRQ allocation failures.
