CVE-2021-47198

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

scsi: lpfc: Fix use-after-free in lpfc_unreg_rpi() routine

An error is detected with the following report when unloading the driver: KASAN: use-after-free in lpfc_unreg_rpi+0x1b1b

The NLP_REG_LOGIN_SEND nlp_flag is set in lpfc_reg_fab_ctrl_node(), but the flag is not cleared upon completion of the login.

This allows a second call to lpfc_unreg_rpi() to proceed with nlp_rpi set to LPFC_RPI_ALLOW_ERROR. This results in a use after free access when used as an rpi_ids array index.

Fix by clearing the NLP_REG_LOGIN_SEND nlp_flag in lpfc_mbx_cmpl_fc_reg_login().

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/79b20beccea3a3938a8500acef4e6b9d7c66142f
• https://git.kernel.org/stable/c/dbebf865b3239595c1d4dba063b122862583b52a