This function, reached through ioctl VS4L_VERTEXIOC_QBUF in the Samsung kernel, has an error case that cannot function correctly. It reads in an array of pointers from userspace and in-place replaces each userspace pointer with a kernel pointer allocated with kzalloc(). Unfortunately, in the error case it will iterate over all the pointers in the array (regardless of how many, if any, were converted to kernel pointers) and call kfree() on each of them. Thus, all it takes to call kfree() on an arbitrary number of controlled pointers is to make the second copy_from_user() fail after successfully copying in the desired number of pointers to free.
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