Advisory Published
CVE Published
Updated

CVE-2024-26798: fbcon: always restore the old font data in fbcon_do_set_font()

First published: Thu Apr 04 2024(Updated: )

In the Linux kernel, the following vulnerability has been resolved: fbcon: always restore the old font data in fbcon_do_set_font() Commit a5a923038d70 (fbdev: fbcon: Properly revert changes when vc_resize() failed) started restoring old font data upon failure (of vc_resize()). But it performs so only for user fonts. It means that the "system"/internal fonts are not restored at all. So in result, the very first call to fbcon_do_set_font() performs no restore at all upon failing vc_resize(). This can be reproduced by Syzkaller to crash the system on the next invocation of font_get(). It's rather hard to hit the allocation failure in vc_resize() on the first font_set(), but not impossible. Esp. if fault injection is used to aid the execution/failure. It was demonstrated by Sirius: BUG: unable to handle page fault for address: fffffffffffffff8 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD cb7b067 P4D cb7b067 PUD cb7d067 PMD 0 Oops: 0000 [#1] PREEMPT SMP KASAN CPU: 1 PID: 8007 Comm: poc Not tainted 6.7.0-g9d1694dc91ce #20 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 RIP: 0010:fbcon_get_font+0x229/0x800 drivers/video/fbdev/core/fbcon.c:2286 Call Trace: <TASK> con_font_get drivers/tty/vt/vt.c:4558 [inline] con_font_op+0x1fc/0xf20 drivers/tty/vt/vt.c:4673 vt_k_ioctl drivers/tty/vt/vt_ioctl.c:474 [inline] vt_ioctl+0x632/0x2ec0 drivers/tty/vt/vt_ioctl.c:752 tty_ioctl+0x6f8/0x1570 drivers/tty/tty_io.c:2803 vfs_ioctl fs/ioctl.c:51 [inline] ... So restore the font data in any case, not only for user fonts. Note the later 'if' is now protected by 'old_userfont' and not 'old_data' as the latter is always set now. (And it is supposed to be non-NULL. Otherwise we would see the bug above again.)

Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 416baaa9-dc9f-4396-8d5f-8c081fb06d67

Affected SoftwareAffected VersionHow to fix
debian/linux
5.10.218-1
5.10.221-1
6.1.94-1
6.1.99-1
6.9.10-1
6.9.12-1
ubuntu/linux<5.15.0-112.122
5.15.0-112.122
ubuntu/linux<6.5.0-44.44
6.5.0-44.44
ubuntu/linux<6.8~
6.8~
ubuntu/linux-aws<5.15.0-1063.69
5.15.0-1063.69
ubuntu/linux-aws<6.8~
6.8~
ubuntu/linux-aws-5.15<5.15.0-1063.69~20.04.1
5.15.0-1063.69~20.04.1
ubuntu/linux-aws-5.15<6.8~
6.8~
ubuntu/linux-aws-5.4<6.8~
6.8~
ubuntu/linux-aws-6.5<6.5.0-1023.23~22.04.1
6.5.0-1023.23~22.04.1
ubuntu/linux-aws-6.5<6.8~
6.8~
ubuntu/linux-aws-fips<6.8~
6.8~
ubuntu/linux-aws-hwe<6.8~
6.8~
ubuntu/linux-azure<5.15.0-1066.75
5.15.0-1066.75
ubuntu/linux-azure<6.8~
6.8~
ubuntu/linux-azure-4.15<6.8~
6.8~
ubuntu/linux-azure-5.15<6.8~
6.8~
ubuntu/linux-azure-5.4<6.8~
6.8~
ubuntu/linux-azure-6.5<6.5.0-1024.25~22.04.1
6.5.0-1024.25~22.04.1
ubuntu/linux-azure-6.5<6.8~
6.8~
ubuntu/linux-azure-fde<5.15.0-1067.76.1
5.15.0-1067.76.1
ubuntu/linux-azure-fde<6.8~
6.8~
ubuntu/linux-azure-fde-5.15<5.15.0-1065.74~20.04.1.1
5.15.0-1065.74~20.04.1.1
ubuntu/linux-azure-fde-5.15<6.8~
6.8~
ubuntu/linux-azure-fips<6.8~
6.8~
ubuntu/linux-bluefield<6.8~
6.8~
ubuntu/linux-fips<6.8~
6.8~
ubuntu/linux-gcp<5.15.0-1062.70
5.15.0-1062.70
ubuntu/linux-gcp<6.5.0-1024.26
6.5.0-1024.26
ubuntu/linux-gcp<6.8~
6.8~
ubuntu/linux-gcp-4.15<6.8~
6.8~
ubuntu/linux-gcp-5.15<5.15.0-1062.70~20.04.1
5.15.0-1062.70~20.04.1
ubuntu/linux-gcp-5.15<6.8~
6.8~
ubuntu/linux-gcp-5.4<6.8~
6.8~
ubuntu/linux-gcp-6.5<6.5.0-1024.26~22.04.1
6.5.0-1024.26~22.04.1
ubuntu/linux-gcp-6.5<6.8~
6.8~
ubuntu/linux-gcp-fips<6.8~
6.8~
ubuntu/linux-gke<5.15.0-1060.66
5.15.0-1060.66
ubuntu/linux-gke<6.8~
6.8~
ubuntu/linux-gkeop<5.15.0-1046.53
5.15.0-1046.53
ubuntu/linux-gkeop<6.8~
6.8~
ubuntu/linux-gkeop-5.15<5.15.0-1046.53~20.04.1
5.15.0-1046.53~20.04.1
ubuntu/linux-gkeop-5.15<6.8~
6.8~
ubuntu/linux-hwe<6.8~
6.8~
ubuntu/linux-hwe-5.15<5.15.0-113.123~20.04.1
5.15.0-113.123~20.04.1
ubuntu/linux-hwe-5.15<6.8~
6.8~
ubuntu/linux-hwe-5.4<6.8~
6.8~
ubuntu/linux-hwe-6.5<6.5.0-44.44~22.04.1
6.5.0-44.44~22.04.1
ubuntu/linux-hwe-6.5<6.8~
6.8~
ubuntu/linux-ibm<5.15.0-1056.59
5.15.0-1056.59
ubuntu/linux-ibm<6.8~
6.8~
ubuntu/linux-ibm-5.15<5.15.0-1057.60~20.04.1
5.15.0-1057.60~20.04.1
ubuntu/linux-ibm-5.15<6.8~
6.8~
ubuntu/linux-ibm-5.4<6.8~
6.8~
ubuntu/linux-intel<6.8~
6.8~
ubuntu/linux-intel-iotg<5.15.0-1058.64
5.15.0-1058.64
ubuntu/linux-intel-iotg<6.8~
6.8~
ubuntu/linux-intel-iotg-5.15<5.15.0-1058.64~20.04.1
5.15.0-1058.64~20.04.1
ubuntu/linux-intel-iotg-5.15<6.8~
6.8~
ubuntu/linux-iot<6.8~
6.8~
ubuntu/linux-kvm<5.15.0-1060.65
5.15.0-1060.65
ubuntu/linux-kvm<6.8~
6.8~
ubuntu/linux-laptop<6.8~
6.8~
ubuntu/linux-lowlatency<5.15.0-110.120
5.15.0-110.120
ubuntu/linux-lowlatency<6.8~
6.8~
ubuntu/linux-lowlatency-hwe-5.15<5.15.0-110.120~20.04.1
5.15.0-110.120~20.04.1
ubuntu/linux-lowlatency-hwe-5.15<6.8~
6.8~
ubuntu/linux-lowlatency-hwe-6.5<6.5.0-44.44.1~22.04.1
6.5.0-44.44.1~22.04.1
ubuntu/linux-lowlatency-hwe-6.5<6.8~
6.8~
ubuntu/linux-lts-xenial<6.8~
6.8~
ubuntu/linux-nvidia<5.15.0-1058.59
5.15.0-1058.59
ubuntu/linux-nvidia<6.8~
6.8~
ubuntu/linux-nvidia-6.5<6.5.0-1023.24
6.5.0-1023.24
ubuntu/linux-nvidia-6.5<6.8~
6.8~
ubuntu/linux-nvidia-6.8<6.8~
6.8~
ubuntu/linux-nvidia-lowlatency<6.8~
6.8~
ubuntu/linux-oem-6.5<6.5.0-1027.28
6.5.0-1027.28
ubuntu/linux-oem-6.5<6.8~
6.8~
ubuntu/linux-oem-6.8<6.8~
6.8~
ubuntu/linux-oracle<5.15.0-1061.67
5.15.0-1061.67
ubuntu/linux-oracle<6.8~
6.8~
ubuntu/linux-oracle-5.15<6.8~
6.8~
ubuntu/linux-oracle-5.4<6.8~
6.8~
ubuntu/linux-oracle-6.5<6.5.0-1026.26~22.04.1
6.5.0-1026.26~22.04.1
ubuntu/linux-oracle-6.5<6.8~
6.8~
ubuntu/linux-raspi<5.15.0-1058.61
5.15.0-1058.61
ubuntu/linux-raspi<6.5.0-1020.23
6.5.0-1020.23
ubuntu/linux-raspi<6.8~
6.8~
ubuntu/linux-raspi-5.4<6.8~
6.8~
ubuntu/linux-riscv<6.8~
6.8~
ubuntu/linux-riscv-5.15<5.15.0-1059.63~20.04.1
5.15.0-1059.63~20.04.1
ubuntu/linux-riscv-5.15<6.8~
6.8~
ubuntu/linux-riscv-6.5<6.8~
6.8~
ubuntu/linux-starfive<6.8~
6.8~
ubuntu/linux-starfive-6.5<6.5.0-1017.18~22.04.1
6.5.0-1017.18~22.04.1
ubuntu/linux-starfive-6.5<6.8~
6.8~
ubuntu/linux-xilinx-zynqmp<5.15.0-1030.34
5.15.0-1030.34
ubuntu/linux-xilinx-zynqmp<6.8~
6.8~

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