From: Zhang Zhengming <zhang.zhengming@xxxxxxx>
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@xxxxxxx
Fixes: 8d62fdebdaf9 ("relay file read: start-pos fix")
Signed-off-by: Zhang Zhengming <zhang.zhengming@xxxxxxx>
Reviewed-by: Zhao Lei <zhao_lei1@xxxxxxxxxxx>
Reviewed-by: Zhou Kete <zhou.kete@xxxxxxx>
Reviewed-by: Pengcheng Yang <yangpc@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/relay.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -989,7 +989,8 @@ 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];
