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

6lowpan: fix NHC entry use-after-free on error path

lowpan_nhc_do_uncompression() looks up an NHC descriptor while holding
lowpan_nhc_lock.  If the descriptor has no uncompress callback, the error
path drops the lock before printing nhc->name.

lowpan_nhc_del() removes descriptors under the same lock and then relies
on synchronize_net() before the owning module can be unloaded.  That only
waits for net RX RCU readers.  lowpan_header_decompress() is also exported
and can be reached from callers that are not necessarily covered by the net
core RX critical section, for example the Bluetooth 6LoWPAN L2CAP receive
path.

This leaves a race where one task drops lowpan_nhc_lock in the error path,
another task unregisters and frees the matching descriptor after
synchronize_net() returns, and the first task then dereferences nhc->name
for the warning.

With the post-unlock window widened, KASAN reports:

  BUG: KASAN: slab-use-after-free in lowpan_nhc_do_uncompression+0x1f4/0x220
  Read of size 8
  lowpan_nhc_do_uncompression
  lowpan_header_decompress

Fix this by printing the warning before dropping lowpan_nhc_lock, so the
descriptor name is read while unregister is still excluded.  The malformed
packet is still rejected with -ENOTSUPP.

https://git.kernel.org/stable/c/0beccbcf50de125be5520d0ffc59af4bb8655482

https://git.kernel.org/stable/c/1720db928e5a58ca7d75ac1d514c3b73fd7061a7

https://git.kernel.org/stable/c/593b78bb3c7ef0c6e9ae6fdf5afa80a5f7573168

https://git.kernel.org/stable/c/80b5c8779acee0550845394fb3e5176a398aa24c

https://git.kernel.org/stable/c/9c2f5c0829a8c8b904dae36be6d8056b719ac605

https://git.kernel.org/stable/c/a8e3a94711134e898c6021a6b77374efa91b3639

https://git.kernel.org/stable/c/b713aa0cc344f10f7a9928a230b5f5e780d04078

https://git.kernel.org/stable/c/cc27aea4d454abfb385ee2c9499c78b96db9b728

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