From: Zhang Zhengming zhang.zhengming@h3c.com
commit 43ec16f1450f4936025a9bdf1a273affdb9732c1 upstream.
There is a crash in relay_file_read, as the var from point to the end of last subbuf.
The oops looks something like: pc : __arch_copy_to_user+0x180/0x310 lr : relay_file_read+0x20c/0x2c8 Call trace: __arch_copy_to_user+0x180/0x310 full_proxy_read+0x68/0x98 vfs_read+0xb0/0x1d0 ksys_read+0x6c/0xf0 __arm64_sys_read+0x20/0x28 el0_svc_common.constprop.3+0x84/0x108 do_el0_svc+0x74/0x90 el0_svc+0x1c/0x28 el0_sync_handler+0x88/0xb0 el0_sync+0x148/0x180
We get the condition by analyzing the vmcore:
1). The last produced byte and last consumed byte both at the end of the last subbuf
2). A softirq calls function(e.g __blk_add_trace) to write relay buffer occurs when an program is calling relay_file_read_avail().
relay_file_read relay_file_read_avail relay_file_read_consume(buf, 0, 0); //interrupted by softirq who will write subbuf .... return 1; //read_start point to the end of the last subbuf read_start = relay_file_read_start_pos //avail is equal to subsize avail = relay_file_read_subbuf_avail //from points to an invalid memory address from = buf->start + read_start //system is crashed copy_to_user(buffer, from, avail)
Link: https://lkml.kernel.org/r/20230419040203.37676-1-zhang.zhengming@h3c.com Fixes: 8d62fdebdaf9 ("relay file read: start-pos fix") Signed-off-by: Zhang Zhengming zhang.zhengming@h3c.com Reviewed-by: Zhao Lei zhao_lei1@hoperun.com Reviewed-by: Zhou Kete zhou.kete@h3c.com Reviewed-by: Pengcheng Yang yangpc@wangsu.com Cc: Jens Axboe axboe@kernel.dk Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/relay.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/kernel/relay.c +++ b/kernel/relay.c @@ -1077,7 +1077,8 @@ static size_t relay_file_read_start_pos( size_t subbuf_size = buf->chan->subbuf_size; size_t n_subbufs = buf->chan->n_subbufs; size_t consumed = buf->subbufs_consumed % n_subbufs; - size_t read_pos = consumed * subbuf_size + buf->bytes_consumed; + size_t read_pos = (consumed * subbuf_size + buf->bytes_consumed) + % (n_subbufs * subbuf_size);
read_subbuf = read_pos / subbuf_size; padding = buf->padding[read_subbuf];