CVE-2022-49761

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

btrfs: always report error in run_one_delayed_ref()

Currently we have a btrfs_debug() for run_one_delayed_ref() failure, but if end users hit such problem, there will be no chance that btrfs_debug() is enabled. This can lead to very little useful info for debugging.

This patch will:

• Add extra info for error reporting Including:

  • logical bytenr
  • num_bytes
  • type
  • action
  • ref_mod

• Replace the btrfs_debug() with btrfs_err()

• Move the error reporting into run_one_delayed_ref() This is to avoid use-after-free, the @node can be freed in the caller.

This error should only be triggered at most once.

As if run_one_delayed_ref() failed, we trigger the error message, then causing the call chain to error out:

btrfs_run_delayed_refs() - btrfs_run_delayed_refs() - btrfs_run_delayed_refs_for_head() `- run_one_delayed_ref()

And we will abort the current transaction in btrfs_run_delayed_refs(). If we have to run delayed refs for the abort transaction, run_one_delayed_ref() will just cleanup the refs and do nothing, thus no new error messages would be output.

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/18bd1c9c02e64a3567f90c83c2c8b855531c8098
• https://git.kernel.org/stable/c/39f501d68ec1ed5cd5c66ac6ec2a7131c517bb92
• https://git.kernel.org/stable/c/853ffa1511b058c79a4c9bb1407b3b20ce311792
• https://git.kernel.org/stable/c/fdb4a70bb768d2a87890409597529ad81cb3de8a