Re: [RFC][PATCHSET] iov_iter work

[Qian Cai]

On 6/6/2021 3:07 PM, Al Viro wrote:
> 	Large part of the problems with iov_iter comes from its history -
> it was not designed, it accreted over years.  Worse, its users sit on
> rather hots paths, so touching any of the primitives can come with
> considerable performance cost.

Al, a quick fuzzing on today's linux-next triggered this. I never saw this before, so I am wondering if this is anything to do with this series. I could try to narrow it down and bisect if necessary. Any thoughts?

[ 1904.633865][T14444] BUG: KASAN: stack-out-of-bounds in iov_iter_revert+0x65c/0x760
[ 1904.641445][T14444] Read of size 8 at addr ffff80002692faf8 by task trinity-c30/14444
[ 1904.649275][T14444]
[ 1904.651461][T14444] CPU: 28 PID: 14444 Comm: trinity-c30 Not tainted 5.13.0-rc5-next-20210610+ #24
[ 1904.660419][T14444] Hardware name: MiTAC RAPTOR EV-883832-X3-0001/RAPTOR, BIOS 1.6 06/28/2020
[ 1904.668944][T14444] Call trace:
[ 1904.672084][T14444]  dump_backtrace+0x0/0x3b8
[ 1904.676445][T14444]  show_stack+0x20/0x30
[ 1904.680454][T14444]  dump_stack_lvl+0x144/0x190
[ 1904.684987][T14444]  print_address_description.constprop.0+0xd0/0x3c8
[ 1904.691432][T14444]  kasan_report+0x1f0/0x208
[ 1904.695787][T14444]  __asan_report_load8_noabort+0x34/0x60
[ 1904.701274][T14444]  iov_iter_revert+0x65c/0x760
iov_iter_revert at /usr/src/linux-next/lib/iov_iter.c:1118
(inlined by) iov_iter_revert at /usr/src/linux-next/lib/iov_iter.c:1058
[ 1904.705891][T14444]  netlink_sendmsg+0x870/0xa18
netlink_sendmsg at /usr/src/linux-next/net/netlink/af_netlink.c:1913
[ 1904.710511][T14444]  sock_write_iter+0x208/0x358
sock_sendmsg_nosec at /usr/src/linux-next/net/socket.c:657
(inlined by) sock_sendmsg at /usr/src/linux-next/net/socket.c:674
(inlined by) sock_write_iter at /usr/src/linux-next/net/socket.c:1001
[ 1904.715128][T14444]  do_iter_readv_writev+0x2e8/0x598
[ 1904.720180][T14444]  do_iter_write+0x110/0x4d0
[ 1904.724622][T14444]  vfs_writev+0x120/0xa00
[ 1904.728805][T14444]  do_writev+0x1a0/0x1e8
[ 1904.732900][T14444]  __arm64_sys_writev+0x78/0xa8
[ 1904.737604][T14444]  invoke_syscall.constprop.0+0xdc/0x1d8
[ 1904.743091][T14444]  do_el0_svc+0xe4/0x298
[ 1904.747187][T14444]  el0_svc+0x20/0x30
[ 1904.750934][T14444]  el0t_64_sync_handler+0xb0/0xb8
[ 1904.755811][T14444]  el0t_64_sync+0x178/0x17c
[ 1904.760168][T14444]
[ 1904.762352][T14444]
[ 1904.764533][T14444] addr ffff80002692faf8 is located in stack of task trinity-c30/14444 at offset 152 in frame:
[ 1904.774617][T14444]  vfs_writev+0x8/0xa00
[ 1904.778629][T14444]
[ 1904.780810][T14444] this frame has 3 objects:
[ 1904.785164][T14444]  [48, 56) 'iov'
[ 1904.785171][T14444]  [80, 120) 'iter'
[ 1904.788656][T14444]  [160, 288) 'iovstack'
[ 1904.792315][T14444]
[ 1904.798582][T14444] Memory state around the buggy address:
[ 1904.804065][T14444]  ffff80002692f980: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[ 1904.811979][T14444]  ffff80002692fa00: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
[ 1904.819892][T14444] >ffff80002692fa80: 00 00 00 f2 f2 f2 00 00 00 00 00 f2 f2 f2 f2 f2
[ 1904.827806][T14444]                                                                 ^
[ 1904.835638][T14444]  ffff80002692fb00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[ 1904.843554][T14444]  ffff80002692fb80: f3 f3 f3 f3 00 00 00 00 00 00 00 00 00 00 00 00