binder: prevent UAF read in print_binder_transaction_log_entry()

binder: prevent UAF read in print_binder_transaction_log_entry()

When a binder transaction is initiated on a binder device coming from a
binderfs instance, a pointer to the name of the binder device is stashed
in the binder_transaction_log_entry's context_name member. Later on it
is used to print the name in print_binder_transaction_log_entry(). By
the time print_binder_transaction_log_entry() accesses context_name
binderfs_evict_inode() might have already freed the associated memory
thereby causing a UAF. Do the simple thing and prevent this by copying
the name of the binder device instead of stashing a pointer to it.

Reported-by: Jann Horn <[email protected]>
Fixes: 03e2e07e3814 ("binder: Make transaction_log available in binderfs")
Link: https://lore.kernel.org/r/CAG48ez14Q0-F8LqsvcNbyR2o6gPW8SHXsm4u5jmD9MpsteM2Tw@mail.gmail.com
Signed-off-by: Christian Brauner <[email protected]>
Reviewed-by: Joel Fernandes (Google) <[email protected]>
Acked-by: Todd Kjos <[email protected]>
Reviewed-by: Hridya Valsaraju <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>