CVE-2021-47427

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

scsi: iscsi: Fix iscsi_task use after free

Commit d39df158518c (scsi: iscsi: Have abort handler get ref to conn) added iscsi_get_conn()/iscsi_put_conn() calls during abort handling but then also changed the handling of the case where we detect an already completed task where we now end up doing a goto to the common put/cleanup code. This results in a iscsi_task use after free, because the common cleanup code will do a put on the iscsi_task.

This reverts the goto and moves the iscsi_get_conn() to after weve checked if the iscsi_task is valid.

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/1642f51ac0d4f2b55d5748094c49ff8f7191b93c
• https://git.kernel.org/stable/c/258aad75c62146453d03028a44f2f1590d58e1f6
• https://git.kernel.org/stable/c/1642f51ac0d4f2b55d5748094c49ff8f7191b93c
• https://git.kernel.org/stable/c/258aad75c62146453d03028a44f2f1590d58e1f6