CVE-2024-44933 in Linux
Summary
by MITRE • 08/26/2024
In the Linux kernel, the following vulnerability has been resolved:
bnxt_en : Fix memory out-of-bounds in bnxt_fill_hw_rss_tbl()
A recent commit has modified the code in __bnxt_reserve_rings() to set the default RSS indirection table to default only when the number of RX rings is changing. While this works for newer firmware that requires RX ring reservations, it causes the regression on older firmware not requiring RX ring resrvations (BNXT_NEW_RM() returns false).
With older firmware, RX ring reservations are not required and so hw_resc->resv_rx_rings is not always set to the proper value. The comparison:
if (old_rx_rings != bp->hw_resc.resv_rx_rings)
in __bnxt_reserve_rings() may be false even when the RX rings are changing. This will cause __bnxt_reserve_rings() to skip setting the default RSS indirection table to default to match the current number of RX rings. This may later cause bnxt_fill_hw_rss_tbl() to use an out-of-range index.
We already have bnxt_check_rss_tbl_no_rmgr() to handle exactly this scenario. We just need to move it up in bnxt_need_reserve_rings() to be called unconditionally when using older firmware. Without the fix, if the TX rings are changing, we'll skip the bnxt_check_rss_tbl_no_rmgr() call and __bnxt_reserve_rings() may also skip the bnxt_set_dflt_rss_indir_tbl() call for the reason explained in the last paragraph. Without setting the default RSS indirection table to default, it causes the regression:
BUG: KASAN: slab-out-of-bounds in __bnxt_hwrm_vnic_set_rss+0xb79/0xe40 Read of size 2 at addr ffff8881c5809618 by task ethtool/31525 Call Trace: __bnxt_hwrm_vnic_set_rss+0xb79/0xe40 bnxt_hwrm_vnic_rss_cfg_p5+0xf7/0x460 __bnxt_setup_vnic_p5+0x12e/0x270 __bnxt_open_nic+0x2262/0x2f30 bnxt_open_nic+0x5d/0xf0 ethnl_set_channels+0x5d4/0xb30 ethnl_default_set_doit+0x2f1/0x620
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Analysis
by VulDB Data Team • 08/28/2024
The vulnerability CVE-2024-44933 affects the Linux kernel's bnxt_en driver, specifically within the bnxt_fill_hw_rss_tbl() function where an out-of-bounds memory access occurs due to improper handling of RSS (Receive Side Scaling) indirection table initialization. This flaw manifests when operating with older firmware versions that do not require RX ring reservations, creating a regression in the driver's ability to properly configure hardware resources. The issue stems from a code modification in __bnxt_reserve_rings() that conditionally sets the default RSS indirection table only when RX ring numbers change, but fails to account for the specific behavior of older firmware where hw_resc->resv_rx_rings may not be correctly initialized. The comparison logic if (old_rx_rings != bp->hw_resc.resv_rx_rings) can evaluate to false even when RX rings are actually changing, causing the driver to skip essential RSS table initialization steps that are critical for maintaining proper memory boundaries during hardware resource management.
The technical root cause of this vulnerability aligns with CWE-129, which addresses improper validation of array indices, and CWE-787, concerning out-of-bounds write operations. The flaw specifically impacts the driver's resource reservation logic where the bnxt_check_rss_tbl_no_rmgr() function, designed to handle exactly this scenario with older firmware, is not being invoked unconditionally as required. This conditional execution path failure leads to a situation where the default RSS indirection table is not properly set to match current RX ring counts, creating a memory access violation when the hardware communication layer attempts to use an invalid table index. The kernel's KASAN (Kernel Address Sanitizer) detection reveals a slab-out-of-bounds read operation of size 2 at address ffff8881c5809618, indicating that the driver is attempting to access memory beyond the allocated buffer boundaries during the bnxt_hwrm_vnic_set_rss function call chain.
The operational impact of this vulnerability extends beyond simple memory corruption to potentially compromise system stability and network functionality in environments using affected bnxt_en drivers with older firmware versions. When the RSS table initialization is skipped, subsequent network operations involving hardware resource management may trigger kernel panics or undefined behavior, particularly during channel configuration changes or network interface reinitialization events. The vulnerability affects systems using Broadcom NetXtreme II and related network adapters where the driver must manage hardware resources dynamically, creating a potential denial of service condition. From an ATT&CK perspective, this vulnerability maps to T1059.001 (Command and Scripting Interpreter - PowerShell) through potential exploitation of the kernel memory corruption for privilege escalation, and T1490 (Inhibit System Recovery) due to the possibility of causing system instability. The issue is particularly concerning in server environments where network reliability and system uptime are critical, as it could be exploited to cause intermittent network outages or complete system crashes during normal network operation.
Mitigation strategies for CVE-2024-44933 require immediate application of the kernel patch that ensures bnxt_check_rss_tbl_no_rmgr() is called unconditionally when using older firmware versions, effectively moving this critical function call to the appropriate execution path within bnxt_need_reserve_rings(). System administrators should prioritize updating to kernel versions containing the fix, particularly those addressing the specific logic flow in __bnxt_reserve_rings() and ensuring proper RSS table initialization regardless of firmware version compatibility. Additionally, monitoring for KASAN reports and kernel oops messages related to memory access violations in the bnxt_en driver should be implemented to detect potential exploitation attempts. The fix addresses the fundamental issue by ensuring that the RSS indirection table is properly initialized to match current hardware resource configurations, preventing the out-of-bounds memory access that occurs when older firmware versions do not correctly set the resv_rx_rings field. Organizations should also consider implementing firmware version compatibility checks and maintaining updated driver versions to prevent similar regressions in other network driver components that may exhibit similar conditional resource management logic patterns.