Description
In the Linux kernel, the following vulnerability has been resolved: fbcon: Set fb_display[i]->mode to NULL when the mode is released Recently, we discovered the following issue through syzkaller: BUG: KASAN: slab-use-after-free in fb_mode_is_equal+0x285/0x2f0 Read of size 4 at addr ff11000001b3c69c by task syz.xxx ... Call Trace: <TASK> dump_stack_lvl+0xab/0xe0 print_address_description.constprop.0+0x2c/0x390 print_report+0xb9/0x280 kasan_report+0xb8/0xf0 fb_mode_is_equal+0x285/0x2f0 fbcon_mode_deleted+0x129/0x180 fb_set_var+0xe7f/0x11d0 do_fb_ioctl+0x6a0/0x750 fb_ioctl+0xe0/0x140 __x64_sys_ioctl+0x193/0x210 do_syscall_64+0x5f/0x9c0 entry_SYSCALL_64_after_hwframe+0x76/0x7e Based on experimentation and analysis, during framebuffer unregistration, only the memory of fb_info->modelist is freed, without setting the corresponding fb_display[i]->mode to NULL for the freed modes. This leads to UAF issues during subsequent accesses. Here's an example of reproduction steps: 1. With /dev/fb0 already registered in the system, load a kernel module to register a new device /dev/fb1; 2. Set fb1's mode to the global fb_display[] array (via FBIOPUT_CON2FBMAP); 3. Switch console from fb to VGA (to allow normal rmmod of the ko); 4. Unload the kernel module, at this point fb1's modelist is freed, leaving a wild pointer in fb_display[]; 5. Trigger the bug via system calls through fb0 attempting to delete a mode from fb0. Add a check in do_unregister_framebuffer(): if the mode to be freed exists in fb_display[], set the corresponding mode pointer to NULL.
Product status
1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (git) before 4ac18f0e6a6d599ca751c4cd98e522afc8e3d4eb
1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (git) before 468f78276a37f4c6499385a4ce28f4f57be6655d
1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (git) before c079d42f70109512eee49123a843be91d8fa133f
1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (git) before de89d19f4f30d9a8de87b9d08c1bd35cb70576d8
1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (git) before a1f3058930745d2b938b6b4f5bd9630dc74b26b7
6.1.159 (semver)
6.6.117 (semver)
6.12.58 (semver)
6.17.8 (semver)
6.18 (original_commit_for_fix)
References
git.kernel.org/...c/4ac18f0e6a6d599ca751c4cd98e522afc8e3d4eb
git.kernel.org/...c/468f78276a37f4c6499385a4ce28f4f57be6655d
git.kernel.org/...c/c079d42f70109512eee49123a843be91d8fa133f
git.kernel.org/...c/de89d19f4f30d9a8de87b9d08c1bd35cb70576d8
git.kernel.org/...c/a1f3058930745d2b938b6b4f5bd9630dc74b26b7
