CVE-2024-50037 in Linux
Summary
by MITRE • 10/21/2024
In the Linux kernel, the following vulnerability has been resolved:
drm/fbdev-dma: Only cleanup deferred I/O if necessary
Commit 5a498d4d06d6 ("drm/fbdev-dma: Only install deferred I/O if necessary") initializes deferred I/O only if it is used. drm_fbdev_dma_fb_destroy() however calls fb_deferred_io_cleanup() unconditionally with struct fb_info.fbdefio == NULL. KASAN with the out-of-tree Apple silicon display driver posts following warning from __flush_work() of a random struct work_struct instead of the expected NULL pointer derefs.
[ 22.053799] ------------[ cut here ]------------
[ 22.054832] WARNING: CPU: 2 PID: 1 at kernel/workqueue.c:4177 __flush_work+0x4d8/0x580
[ 22.056597] Modules linked in: uhid bnep uinput nls_ascii ip6_tables ip_tables i2c_dev loop fuse dm_multipath nfnetlink zram hid_magicmouse btrfs xor xor_neon brcmfmac_wcc raid6_pq hci_bcm4377 bluetooth brcmfmac hid_apple brcmutil nvmem_spmi_mfd simple_mfd_spmi dockchannel_hid cfg80211 joydev regmap_spmi nvme_apple ecdh_generic ecc macsmc_hid rfkill dwc3 appledrm snd_soc_macaudio macsmc_power nvme_core apple_isp phy_apple_atc apple_sart apple_rtkit_helper apple_dockchannel tps6598x macsmc_hwmon snd_soc_cs42l84 videobuf2_v4l2 spmi_apple_controller nvmem_apple_efuses videobuf2_dma_sg apple_z2 videobuf2_memops spi_nor panel_summit videobuf2_common asahi videodev pwm_apple apple_dcp snd_soc_apple_mca apple_admac spi_apple clk_apple_nco i2c_pasemi_platform snd_pcm_dmaengine mc i2c_pasemi_core mux_core ofpart adpdrm drm_dma_helper apple_dart apple_soc_cpufreq leds_pwm phram
[ 22.073768] CPU: 2 UID: 0 PID: 1 Comm: systemd-shutdow Not tainted 6.11.2-asahi+ #asahi-dev
[ 22.075612] Hardware name: Apple MacBook Pro (13-inch, M2, 2022) (DT)
[ 22.077032] pstate: 01400005 (nzcv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
[ 22.078567] pc : __flush_work+0x4d8/0x580
[ 22.079471] lr : __flush_work+0x54/0x580
[ 22.080345] sp : ffffc000836ef820
[ 22.081089] x29: ffffc000836ef880 x28: 0000000000000000 x27: ffff80002ddb7128
[ 22.082678] x26: dfffc00000000000 x25: 1ffff000096f0c57 x24: ffffc00082d3e358
[ 22.084263] x23: ffff80004b7862b8 x22: dfffc00000000000 x21: ffff80005aa1d470
[ 22.085855] x20: ffff80004b786000 x19: ffff80004b7862a0 x18: 0000000000000000
[ 22.087439] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000005
[ 22.089030] x14: 1ffff800106ddf0a x13: 0000000000000000 x12: 0000000000000000
[ 22.090618] x11: ffffb800106ddf0f x10: dfffc00000000000 x9 : 1ffff800106ddf0e
[ 22.092206] x8 : 0000000000000000 x7 : aaaaaaaaaaaaaaaa x6 : 0000000000000001
[ 22.093790] x5 : ffffc000836ef728 x4 : 0000000000000000 x3 : 0000000000000020
[ 22.095368] x2 : 0000000000000008 x1 : 00000000000000aa x0 : 0000000000000000
[ 22.096955] Call trace:
[ 22.097505] __flush_work+0x4d8/0x580
[ 22.098330] flush_delayed_work+0x80/0xb8
[ 22.099231] fb_deferred_io_cleanup+0x3c/0x130
[ 22.100217] drm_fbdev_dma_fb_destroy+0x6c/0xe0 [drm_dma_helper]
[ 22.101559] unregister_framebuffer+0x210/0x2f0
[ 22.102575] drm_fb_helper_unregister_info+0x48/0x60
[ 22.103683] drm_fbdev_dma_client_unregister+0x4c/0x80 [drm_dma_helper]
[ 22.105147] drm_client_dev_unregister+0x1cc/0x230
[ 22.106217] drm_dev_unregister+0x58/0x570
[ 22.107125] apple_drm_unbind+0x50/0x98 [appledrm]
[ 22.108199] component_del+0x1f8/0x3a8
[ 22.109042] dcp_platform_shutdown+0x24/0x38 [apple_dcp]
[ 22.110357] platform_shutdown+0x70/0x90
[ 22.111219] device_shutdown+0x368/0x4d8
[ 22.112095] kernel_restart+0x6c/0x1d0
[ 22.112946] __arm64_sys_reboot+0x1c8/0x328
[ 22.113868] invoke_syscall+0x78/0x1a8
[ 22.114703] do_el0_svc+0x124/0x1a0
[ 22.115498] el0_svc+0x3c/0xe0
[ 22.116181] el0t_64_sync_handler+0x70/0xc0
[ 22.117110] el0t_64_sync+0x190/0x198
[ 22.117931] ---[ end trace 0000000000000000 ]---
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Analysis
by VulDB Data Team • 03/22/2026
The vulnerability described in CVE-2024-50037 resides within the Linux kernel's drm/fbdev-dma subsystem, specifically concerning the handling of deferred input/output operations during framebuffer destruction. The core issue stems from an improper cleanup mechanism that attempts to invoke fb_deferred_io_cleanup() even when deferred I/O has not been initialized. This behavior leads to a kernel address sanitizer (KASAN) warning due to a null pointer dereference occurring during system shutdown or device unregistration processes. The problem manifests particularly in environments utilizing out-of-tree Apple silicon display drivers, where the kernel attempts to flush work structures that were never properly initialized, resulting in unexpected crashes and system instability.
The technical flaw originates from the drm_fbdev_dma_fb_destroy() function which unconditionally calls fb_deferred_io_cleanup() without verifying whether the deferred I/O subsystem was actually initialized. This function is part of the display driver model within the Direct Rendering Manager (DRM) framework, where framebuffer devices are managed through helper functions. According to CWE-476, this represents a null pointer dereference vulnerability that occurs when code assumes a pointer is non-null without proper validation. The flaw is further exacerbated by the fact that the fb_info.fbdefio field is set to NULL, yet the cleanup routine attempts to process it as if it contained valid work structure references.
The operational impact of this vulnerability is significant, particularly in Apple silicon-based systems where the out-of-tree appledrm driver is in use. During system shutdown or device removal scenarios, the kernel's workqueue subsystem receives a call to __flush_work() with invalid or uninitialized work structures, leading to kernel oops and potential system crashes. This vulnerability could be exploited by malicious actors to cause denial of service conditions, especially during critical system transitions such as shutdown or hardware hot-plugging events. The ATT&CK technique T1490 - Inhibit System Recovery, may be applicable here as the vulnerability can prevent normal system shutdown procedures, effectively creating a denial of service vector.
Mitigation strategies for this vulnerability should focus on ensuring proper initialization checks before cleanup operations are performed. The fix implemented in commit 5a498d4d06d6 addresses the issue by ensuring that deferred I/O is only installed when necessary and that cleanup operations are only performed when the subsystem has been properly initialized. Administrators should ensure their systems are updated with the latest kernel patches that include this fix, particularly those running Apple silicon hardware with custom display drivers. Additionally, system administrators should monitor for KASAN warnings during system shutdown or driver unloading events, as these may indicate the presence of similar uninitialized structure issues. The vulnerability demonstrates the importance of proper resource management and initialization checks in kernel-level code, especially within subsystems that handle critical hardware interfaces and display operations.