CVE-2021-47482

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

net: batman-adv: fix error handling

Syzbot reported ODEBUG warning in batadv_nc_mesh_free(). The problem was in wrong error handling in batadv_mesh_init().

Before this patch batadv_mesh_init() was calling batadv_mesh_free() in case of any batadv_*_init() calls failure. This approach may work well, when there is some kind of indicator, which can tell which parts of batadv are initialized; but there isnt any.

All written above lead to cleaning up uninitialized fields. Even if we hide ODEBUG warning by initializing bat_priv->nc.work, syzbot was able to hit GPF in batadv_nc_purge_paths(), because hash pointer in still NULL. [1]

To fix these bugs we can unwind batadv_init() calls one by one. It is good approach for 2 reasons: 1) It fixes bugs on error handling path 2) It improves the performance, since we wont call unneeded batadv_free() functions.

So, this patch makes all batadv_init() clean up all allocated memory before returning with an error to no call correspoing batadv_free() and open-codes batadv_mesh_free() with proper order to avoid touching uninitialized fields.

Weakness

The product does not use a standardized method for handling errors throughout the code, which might introduce inconsistent error handling and resultant weaknesses.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/07533f1a673ce1126d0a72ef1e4b5eaaa3dd6d20
• https://git.kernel.org/stable/c/0c6b199f09be489c48622537a550787fc80aea73
• https://git.kernel.org/stable/c/6422e8471890273994fe8cc6d452b0dcd2c9483e
• https://git.kernel.org/stable/c/6f68cd634856f8ca93bafd623ba5357e0f648c68
• https://git.kernel.org/stable/c/a8f7359259dd5923adc6129284fdad12fc5db347
• https://git.kernel.org/stable/c/b0a2cd38553c77928ef1646ed1518486b1e70ae8
• https://git.kernel.org/stable/c/e50f957652190b5a88a8ebce7e5ab14ebd0d3f00
• https://git.kernel.org/stable/c/fbf150b16a3635634b7dfb7f229d8fcd643c6c51