UBUNTU-CVE-2024-36963
In the Linux kernel, the following vulnerability has been resolved: tracefs: Reset permissions on remount if permissions are options There's an inconsistency with the way permissions are handled in tracefs. Because the permissions are generated when accessed, they default to the root inode's permission if they were never set by the user. If the user sets the permissions, then a flag is set and the permissions are saved via the inode (for tracefs files) or an internal attribute field (for eventfs). But if a remount happens that specify the permissions, all the files that were not changed by the user gets updated, but the ones that were are not. If the user were to remount the file system with a given permission, then all files and directories within that file system should be updated. This can cause security issues if a file's permission was updated but the admin forgot about it. They could incorrectly think that remounting with permissions set would update all files, but miss some. For example: # cd /sys/kernel/tracing # chgrp 1002 current_tracer # ls -l [..] -rw-r----- 1 root root 0 May 1 21:25 buffer_size_kb -rw-r----- 1 root root 0 May 1 21:25 buffer_subbuf_size_kb -r--r----- 1 root root 0 May 1 21:25 buffer_total_size_kb -rw-r----- 1 root lkp 0 May 1 21:25 current_tracer -rw-r----- 1 root root 0 May 1 21:25 dynamic_events -r--r----- 1 root root 0 May 1 21:25 dyn_ftrace_total_info -r--r----- 1 root root 0 May 1 21:25 enabled_functions Where current_tracer now has group "lkp". # mount -o remount,gid=1001 . # ls -l -rw-r----- 1 root tracing 0 May 1 21:25 buffer_size_kb -rw-r----- 1 root tracing 0 May 1 21:25 buffer_subbuf_size_kb -r--r----- 1 root tracing 0 May 1 21:25 buffer_total_size_kb -rw-r----- 1 root lkp 0 May 1 21:25 current_tracer -rw-r----- 1 root tracing 0 May 1 21:25 dynamic_events -r--r----- 1 root tracing 0 May 1 21:25 dyn_ftrace_total_info -r--r----- 1 root tracing 0 May 1 21:25 enabled_functions Everything changed but the "current_tracer". Add a new link list that keeps track of all the tracefs_inodes which has the permission flags that tell if the file/dir should use the root inode's permission or not. Then on remount, clear all the flags so that the default behavior of using the root inode's permission is done for all files and directories.
02 / AFFECTED SOFTWARE
Affected packages
29 explicit affected versions
10 explicit affected versions
1 explicit affected versions
11 explicit affected versions
9 explicit affected versions
2 explicit affected versions
7 explicit affected versions
26 explicit affected versions
37 explicit affected versions
1 explicit affected versions
9 explicit affected versions
10 explicit affected versions
10 explicit affected versions
13 explicit affected versions
13 explicit affected versions
10 explicit affected versions
37 explicit affected versions
7 explicit affected versions
8 explicit affected versions
4 explicit affected versions
8 explicit affected versions
23 explicit affected versions
7 explicit affected versions
10 explicit affected versions
10 explicit affected versions
33 explicit affected versions
16 explicit affected versions
6 explicit affected versions
2 explicit affected versions
12 explicit affected versions
38 explicit affected versions
51 explicit affected versions
13 explicit affected versions
10 explicit affected versions
10 explicit affected versions
13 explicit affected versions
1 explicit affected versions
10 explicit affected versions
3 explicit affected versions
8 explicit affected versions
2 explicit affected versions
8 explicit affected versions
2 explicit affected versions
21 explicit affected versions
6 explicit affected versions
13 explicit affected versions
12 explicit affected versions
7 explicit affected versions
12 explicit affected versions
26 explicit affected versions
7 explicit affected versions
7 explicit affected versions
23 explicit affected versions
3 explicit affected versions
5 explicit affected versions
3 explicit affected versions
3 explicit affected versions
26 explicit affected versions
12 explicit affected versions
44 explicit affected versions
1 explicit affected versions
4 explicit affected versions
4 explicit affected versions
16 explicit affected versions
9 explicit affected versions
12 explicit affected versions
13 explicit affected versions
7 explicit affected versions
9 explicit affected versions
5 explicit affected versions
7 explicit affected versions
10 explicit affected versions
14 explicit affected versions
18 explicit affected versions
3 explicit affected versions
16 explicit affected versions
43 explicit affected versions
4 explicit affected versions
11 explicit affected versions
35 explicit affected versions
12 explicit affected versions
6 explicit affected versions
12 explicit affected versions
50 explicit affected versions
12 explicit affected versions
27 explicit affected versions
12 explicit affected versions
7 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
In the Linux kernel, the following vulnerability has been resolved: tracefs: Reset permissions on remount if permissions are options There's an inconsistency with the way permissions are handled in tracefs. Because the permissions are generated when accessed, they default to the root inode's permission if they were never set by the user. If the user sets the permissions, then a flag is set and the permissions are saved via the inode (for tracefs files) or an internal attribute field (for eventfs). But if a remount happens that specify the permissions, all the files that were not changed by the user gets updated, but the ones that were are not. If the user were to remount the file system with a given permission, then all files and directories within that file system should be updated. This can cause security issues if a file's permission was updated but the admin forgot about it. They could incorrectly think that remounting with permissions set would update all files, but miss some. For example: # cd /sys/kernel/tracing # chgrp 1002 current_tracer # ls -l [..] -rw-r----- 1 root root 0 May 1 21:25 buffer_size_kb -rw-r----- 1 root root 0 May 1 21:25 buffer_subbuf_size_kb -r--r----- 1 root root 0 May 1 21:25 buffer_total_size_kb -rw-r----- 1 root lkp 0 May 1 21:25 current_tracer -rw-r----- 1 root root 0 May 1 21:25 dynamic_events -r--r----- 1 root root 0 May 1 21:25 dyn_ftrace_total_info -r--r----- 1 root root 0 May 1 21:25 enabled_functions Where current_tracer now has group "lkp". # mount -o remount,gid=1001 . # ls -l -rw-r----- 1 root tracing 0 May 1 21:25 buffer_size_kb -rw-r----- 1 root tracing 0 May 1 21:25 buffer_subbuf_size_kb -r--r----- 1 root tracing 0 May 1 21:25 buffer_total_size_kb -rw-r----- 1 root lkp 0 May 1 21:25 current_tracer -rw-r----- 1 root tracing 0 May 1 21:25 dynamic_events -r--r----- 1 root tracing 0 May 1 21:25 dyn_ftrace_total_info -r--r----- 1 root tracing 0 May 1 21:25 enabled_functions Everything changed but the "current_tracer". Add a new link list that keeps track of all the tracefs_inodes which has the permission flags that tell if the file/dir should use the root inode's permission or not. Then on remount, clear all the flags so that the default behavior of using the root inode's permission is done for all files and directories.
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/baa23a8d4360d981a49913841a726edede5cdd54
- https://git.kernel.org/stable/c/414fb08628143203d29ccd0264b5a83fb9523c03
- https://git.kernel.org/stable/c/5f91fc82794d4a6e41cdcd02d00baa377d94ca78
- https://git.kernel.org/stable/c/baa23a8d4360d981a49913841a726edede5cdd54
- https://ubuntu.com/security/CVE-2024-36963
- https://ubuntu.com/security/notices/USN-6949-1
- https://ubuntu.com/security/notices/USN-6949-2
- https://ubuntu.com/security/notices/USN-6952-1
- https://ubuntu.com/security/notices/USN-6952-2
- https://ubuntu.com/security/notices/USN-6955-1
- https://www.cve.org/CVERecord?id=CVE-2024-36963