UBUNTU-CVE-2024-26798
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.)
02 / AFFECTED SOFTWARE
Affected packages
50 explicit affected versions
6 explicit affected versions
12 explicit affected versions
1 explicit affected versions
9 explicit affected versions
29 explicit affected versions
43 explicit affected versions
12 explicit affected versions
18 explicit affected versions
6 explicit affected versions
52 explicit affected versions
7 explicit affected versions
38 explicit affected versions
49 explicit affected versions
38 explicit affected versions
10 explicit affected versions
45 explicit affected versions
46 explicit affected versions
11 explicit affected versions
35 explicit affected versions
5 explicit affected versions
14 explicit affected versions
7 explicit affected versions
18 explicit affected versions
7 explicit affected versions
33 explicit affected versions
13 explicit affected versions
12 explicit affected versions
4 explicit affected versions
23 explicit affected versions
21 explicit affected versions
9 explicit affected versions
16 explicit affected versions
10 explicit affected versions
36 explicit affected versions
12 explicit affected versions
12 explicit affected versions
7 explicit affected versions
12 explicit affected versions
10 explicit affected versions
37 explicit affected versions
11 explicit affected versions
10 explicit affected versions
25 explicit affected versions
26 explicit affected versions
13 explicit affected versions
4 explicit affected versions
29 explicit affected versions
13 explicit affected versions
10 explicit affected versions
49 explicit affected versions
47 explicit affected versions
9 explicit affected versions
33 explicit affected versions
23 explicit affected versions
10 explicit affected versions
11 explicit affected versions
12 explicit affected versions
7 explicit affected versions
12 explicit affected versions
37 explicit affected versions
30 explicit affected versions
46 explicit affected versions
49 explicit affected versions
26 explicit affected versions
1 explicit affected versions
13 explicit affected versions
16 explicit affected versions
39 explicit affected versions
3 explicit affected versions
2 explicit affected versions
51 explicit affected versions
2 explicit affected versions
8 explicit affected versions
12 explicit affected versions
35 explicit affected versions
27 explicit affected versions
21 explicit affected versions
10 explicit affected versions
5 explicit affected versions
8 explicit affected versions
10 explicit affected versions
11 explicit affected versions
26 explicit affected versions
13 explicit affected versions
7 explicit affected versions
41 explicit affected versions
10 explicit affected versions
12 explicit affected versions
12 explicit affected versions
44 explicit affected versions
16 explicit affected versions
3 explicit affected versions
13 explicit affected versions
35 explicit affected versions
37 explicit affected versions
12 explicit affected versions
38 explicit affected versions
39 explicit affected versions
9 explicit affected versions
38 explicit affected versions
11 explicit affected versions
46 explicit affected versions
8 explicit affected versions
7 explicit affected versions
20 explicit affected versions
4 explicit affected versions
1 explicit affected versions
44 explicit affected versions
11 explicit affected versions
43 explicit affected versions
10 explicit affected versions
8 explicit affected versions
14 explicit affected versions
4 explicit affected versions
9 explicit affected versions
1 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
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.)
05 / REFERENCES
Further evidence
- https://git.kernel.org/stable/c/00d6a284fcf3fad1b7e1b5bc3cd87cbfb60ce03f
- https://git.kernel.org/stable/c/20a4b5214f7bee13c897477168c77bbf79683c3d
- https://git.kernel.org/stable/c/2f91a96b892fab2f2543b4a55740c5bee36b1a6b
- https://git.kernel.org/stable/c/73a6bd68a1342f3a44cac9dffad81ad6a003e520
- https://git.kernel.org/stable/c/a2c881413dcc5d801bdc9535e51270cc88cb9cd8
- https://ubuntu.com/security/CVE-2024-26798
- https://ubuntu.com/security/notices/USN-6820-1
- https://ubuntu.com/security/notices/USN-6820-2
- https://ubuntu.com/security/notices/USN-6821-1
- https://ubuntu.com/security/notices/USN-6821-2
- https://ubuntu.com/security/notices/USN-6821-3
- https://ubuntu.com/security/notices/USN-6821-4
- https://ubuntu.com/security/notices/USN-6828-1
- https://ubuntu.com/security/notices/USN-6871-1
- https://ubuntu.com/security/notices/USN-6892-1
- https://ubuntu.com/security/notices/USN-6895-1
- https://ubuntu.com/security/notices/USN-6895-2
- https://ubuntu.com/security/notices/USN-6895-3
- https://ubuntu.com/security/notices/USN-6895-4
- https://ubuntu.com/security/notices/USN-6900-1
- https://ubuntu.com/security/notices/USN-6919-1
- https://www.cve.org/CVERecord?id=CVE-2024-26798