CVE-2021-47026

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

RDMA/rtrs-clt: destroy sysfs after removing session from active list

A session can be removed dynamically by sysfs interface remove_path that eventually calls rtrs_clt_remove_path_from_sysfs function. The current rtrs_clt_remove_path_from_sysfs first removes the sysfs interfaces and frees sess->stats object. Second it removes the session from the active list.

Therefore some functions could access non-connected session and access the freed sess->stats object even-if they check the session status before accessing the session.

For instance rtrs_clt_request and get_next_path_min_inflight check the session status and try to send IO to the session. The session status could be changed when they are trying to send IO but they could not catch the change and update the statistics information in sess->stats object, and generate use-after-free problem. (see: RDMA/rtrs-clt: Check state of the rtrs_clt_sess before reading its stats)

This patch changes the rtrs_clt_remove_path_from_sysfs to remove the session from the active session list and then destroy the sysfs interfaces.

Each function still should check the session status because closing or error recovery paths can change the status.

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/676171f9405dcaa45a33d18241c32f387dbaae39
• https://git.kernel.org/stable/c/7f4a8592ff29f19c5a2ca549d0973821319afaad
• https://git.kernel.org/stable/c/b64415c6b3476cf9fa4d0aea3807065b8403a937
• https://git.kernel.org/stable/c/d3cca8067d43dfee4a3535c645b55f618708dccb
• https://git.kernel.org/stable/c/676171f9405dcaa45a33d18241c32f387dbaae39
• https://git.kernel.org/stable/c/7f4a8592ff29f19c5a2ca549d0973821319afaad
• https://git.kernel.org/stable/c/b64415c6b3476cf9fa4d0aea3807065b8403a937
• https://git.kernel.org/stable/c/d3cca8067d43dfee4a3535c645b55f618708dccb