splice, net: Fix splice_to_socket() to handle pipe bufs larger than a page
splice_to_socket() assumes that a pipe_buffer won't hold more than a single page of data - but this assumption can be violated by skb_splice_bits() when it splices from a socket into a pipe. The problem is that splice_to_socket() doesn't advance the pipe_buffer length and offset when transcribing from the pipe buf into a bio_vec, so if the buf is >PAGE_SIZE, it keeps repeating the same initial chunk and doesn't advance the tail index. It then subtracts this from "remain" and overcounts the amount of data to be sent. The cleanup phase then tries to overclean the pipe, hits an unused pipe buf and a NULL-pointer dereference occurs. Fix this by not restricting the bio_vec size to PAGE_SIZE and instead transcribing the entirety of each pipe_buffer into a single bio_vec and advancing the tail index if remain hasn't hit zero yet. Large bio_vecs will then be split up by iterator functions such as iov_iter_extract_pages(). This resulted in a KASAN report looking like: general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f] ... RIP: 0010:pipe_buf_release include/linux/pipe_fs_i.h:203 [inline] RIP: 0010:splice_to_socket+0xa91/0xe30 fs/splice.c:933 Fixes: 2dc334f1 ("splice, net: Use sendmsg(MSG_SPLICE_PAGES) rather than ->sendpage()") Reported-by:<syzbot+f9e28a23426ac3b24f20@syzkaller.appspotmail.com> Link: https://lore.kernel.org/r/0000000000000900e905fdeb8e39@google.com/ Tested-by:
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