CVE-2024-26689

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

ceph: prevent use-after-free in encode_cap_msg()

In fs/ceph/caps.c, in encode_cap_msg(), use after free error was caught by KASAN at this line - ceph_buffer_get(arg->xattr_buf);. This implies before the refcount could be increment here, it was freed.

In same file, in handle_cap_grant() refcount is decremented by this line - ceph_buffer_put(ci->i_xattrs.blob);. It appears that a race occurred and resource was freed by the latter line before the former line could increment it.

encode_cap_msg() is called by __send_cap() and __send_cap() is called by ceph_check_caps() after calling __prep_cap(). __prep_cap() is where arg->xattr_buf is assigned to ci->i_xattrs.blob. This is the spot where the refcount must be increased to prevent use after free error.

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/70e329b440762390258a6fe8c0de93c9fdd56c77
• https://git.kernel.org/stable/c/7958c1bf5b03c6f1f58e724dbdec93f8f60b96fc
• https://git.kernel.org/stable/c/8180d0c27b93a6eb60da1b08ea079e3926328214
• https://git.kernel.org/stable/c/ae20db45e482303a20e56f2db667a9d9c54ac7e7
• https://git.kernel.org/stable/c/cda4672da1c26835dcbd7aec2bfed954eda9b5ef
• https://git.kernel.org/stable/c/f3f98d7d84b31828004545e29fd7262b9f444139
• https://git.kernel.org/stable/c/70e329b440762390258a6fe8c0de93c9fdd56c77
• https://git.kernel.org/stable/c/7958c1bf5b03c6f1f58e724dbdec93f8f60b96fc
• https://git.kernel.org/stable/c/8180d0c27b93a6eb60da1b08ea079e3926328214
• https://git.kernel.org/stable/c/ae20db45e482303a20e56f2db667a9d9c54ac7e7
• https://git.kernel.org/stable/c/cda4672da1c26835dcbd7aec2bfed954eda9b5ef
• https://git.kernel.org/stable/c/f3f98d7d84b31828004545e29fd7262b9f444139
• https://lists.debian.org/debian-lts-announce/2024/06/msg00017.html