CVE-2024-26875

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

media: pvrusb2: fix uaf in pvr2_context_set_notify

[Syzbot reported] BUG: KASAN: slab-use-after-free in pvr2_context_set_notify+0x2c4/0x310 drivers/media/usb/pvrusb2/pvrusb2-context.c:35 Read of size 4 at addr ffff888113aeb0d8 by task kworker/1:1/26

CPU: 1 PID: 26 Comm: kworker/1:1 Not tainted 6.8.0-rc1-syzkaller-00046-gf1a27f081c1f #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024 Workqueue: usb_hub_wq hub_event Call Trace: __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106 print_address_description mm/kasan/report.c:377 [inline] print_report+0xc4/0x620 mm/kasan/report.c:488 kasan_report+0xda/0x110 mm/kasan/report.c:601 pvr2_context_set_notify+0x2c4/0x310 drivers/media/usb/pvrusb2/pvrusb2-context.c:35 pvr2_context_notify drivers/media/usb/pvrusb2/pvrusb2-context.c:95 [inline] pvr2_context_disconnect+0x94/0xb0 drivers/media/usb/pvrusb2/pvrusb2-context.c:272

Freed by task 906: kasan_save_stack+0x33/0x50 mm/kasan/common.c:47 kasan_save_track+0x14/0x30 mm/kasan/common.c:68 kasan_save_free_info+0x3f/0x60 mm/kasan/generic.c:640 poison_slab_object mm/kasan/common.c:241 [inline] __kasan_slab_free+0x106/0x1b0 mm/kasan/common.c:257 kasan_slab_free include/linux/kasan.h:184 [inline] slab_free_hook mm/slub.c:2121 [inline] slab_free mm/slub.c:4299 [inline] kfree+0x105/0x340 mm/slub.c:4409 pvr2_context_check drivers/media/usb/pvrusb2/pvrusb2-context.c:137 [inline] pvr2_context_thread_func+0x69d/0x960 drivers/media/usb/pvrusb2/pvrusb2-context.c:158

[Analyze] Task A set disconnect_flag = !0, which resulted in Task Bs condition being met and releasing mp, leading to this issue.

[Fix] Place the disconnect_flag assignment operation after all code in pvr2_context_disconnect() to avoid this issue.

Weakness

Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.

Affected Software

Extended Description

The use of previously-freed memory can have any number of adverse consequences, ranging from the corruption of valid data to the execution of arbitrary code, depending on the instantiation and timing of the flaw. The simplest way data corruption may occur involves the system’s reuse of the freed memory. Use-after-free errors have two common and sometimes overlapping causes:

In this scenario, the memory in question is allocated to another pointer validly at some point after it has been freed. The original pointer to the freed memory is used again and points to somewhere within the new allocation. As the data is changed, it corrupts the validly used memory; this induces undefined behavior in the process. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.

Potential Mitigations

References

• https://git.kernel.org/stable/c/0a0b79ea55de8514e1750884e5fec77f9fdd01ee
• https://git.kernel.org/stable/c/3a1ec89708d2e57e2712f46241282961b1a7a475
• https://git.kernel.org/stable/c/40cd818fae875c424a8335009db33c7b5a07de3a
• https://git.kernel.org/stable/c/8e60b99f6b7ccb3badeb512f5eb613ad45904592
• https://git.kernel.org/stable/c/ab896d93fd6a2cd1afeb034c3cc9226cb499209f
• https://git.kernel.org/stable/c/d29ed08964cec8b9729bc55c7bb23f679d7a18fb
• https://git.kernel.org/stable/c/eaa410e05bdf562c90b23cdf2d9327f9c4625e16
• https://git.kernel.org/stable/c/eb6e9dce979c08210ff7249e5e0eceb8991bfcd7
• https://git.kernel.org/stable/c/ed8000e1e8e9684ab6c30cf2b526c0cea039929c
• https://git.kernel.org/stable/c/0a0b79ea55de8514e1750884e5fec77f9fdd01ee
• https://git.kernel.org/stable/c/3a1ec89708d2e57e2712f46241282961b1a7a475
• https://git.kernel.org/stable/c/40cd818fae875c424a8335009db33c7b5a07de3a
• https://git.kernel.org/stable/c/8e60b99f6b7ccb3badeb512f5eb613ad45904592
• https://git.kernel.org/stable/c/ab896d93fd6a2cd1afeb034c3cc9226cb499209f
• https://git.kernel.org/stable/c/d29ed08964cec8b9729bc55c7bb23f679d7a18fb
• https://git.kernel.org/stable/c/eaa410e05bdf562c90b23cdf2d9327f9c4625e16
• https://git.kernel.org/stable/c/eb6e9dce979c08210ff7249e5e0eceb8991bfcd7
• https://git.kernel.org/stable/c/ed8000e1e8e9684ab6c30cf2b526c0cea039929c
• https://lists.debian.org/debian-lts-announce/2024/06/msg00017.html
• https://lists.debian.org/debian-lts-announce/2024/06/msg00020.html