On Thu, Feb 06, 2020 at 06:47:56AM +0000, Taehee Yoo wrote:
> When the module is being removed, the module state is set to
> MODULE_STATE_GOING. At this point, try_module_get() fails.
> And when {full/open}_proxy_open() is being called,
> it calls try_module_get() to try to hold module reference count.
> If it fails, it warns about the possibility of debugfs file leak.
>
> If {full/open}_proxy_open() is called while the module is being removed,
> it fails to hold the module.
> So, It warns about debugfs file leak. But it is not the debugfs file
> leak case. So, this patch just adds module state checking routine
> in the {full/open}_proxy_open().
>
> Test commands:
> #SHELL1
> while :
> do
> modprobe netdevsim
> echo 1 > /sys/bus/netdevsim/new_device
> modprobe -rv netdevsim
> done
>
> #SHELL2
> while :
> do
> cat /sys/kernel/debug/netdevsim/netdevsim1/ports/0/ipsec
> done
>
> Splat looks like:
> [ 298.766738][T14664] debugfs file owner did not clean up at exit: ipsec
> [ 298.766766][T14664] WARNING: CPU: 2 PID: 14664 at fs/debugfs/file.c:312 full_proxy_open+0x10f/0x650
> [ 298.768595][T14664] Modules linked in: netdevsim(-) openvswitch nsh nf_conncount nf_nat nf_conntrack nf_defrag_ipv6 n][ 298.771343][T14664] CPU: 2 PID: 14664 Comm: cat Tainted: G W 5.5.0+ #1
> [ 298.772373][T14664] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
> [ 298.773545][T14664] RIP: 0010:full_proxy_open+0x10f/0x650
> [ 298.774247][T14664] Code: 48 c1 ea 03 80 3c 02 00 0f 85 c1 04 00 00 49 8b 3c 24 e8 e4 b5 78 ff 84 c0 75 2d 4c 89 ee 48
> [ 298.776782][T14664] RSP: 0018:ffff88805b7df9b8 EFLAGS: 00010282[ 298.777583][T14664] RAX: dffffc0000000008 RBX: ffff8880511725c0 RCX: 0000000000000000
> [ 298.778610][T14664] RDX: 0000000000000000 RSI: 0000000000000006 RDI: ffff8880540c5c14
> [ 298.779637][T14664] RBP: 0000000000000000 R08: fffffbfff15235ad R09: 0000000000000000
> [ 298.780664][T14664] R10: 0000000000000001 R11: 0000000000000000 R12: ffffffffc06b5000
> [ 298.781702][T14664] R13: ffff88804c234a88 R14: ffff88804c22dd00 R15: ffffffff8a1b5660
> [ 298.782722][T14664] FS: 00007fafa13a8540(0000) GS:ffff88806c800000(0000) knlGS:0000000000000000
> [ 298.783845][T14664] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 298.784672][T14664] CR2: 00007fafa0e9cd10 CR3: 000000004b286005 CR4: 00000000000606e0
> [ 298.785739][T14664] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [ 298.786769][T14664] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [ 298.787785][T14664] Call Trace:
> [ 298.788237][T14664] do_dentry_open+0x63c/0xf50
> [ 298.788872][T14664] ? open_proxy_open+0x270/0x270
> [ 298.789524][T14664] ? __x64_sys_fchdir+0x180/0x180
> [ 298.790169][T14664] ? inode_permission+0x65/0x390
> [ 298.790832][T14664] path_openat+0xc45/0x2680
> [ 298.791425][T14664] ? save_stack+0x69/0x80
> [ 298.791988][T14664] ? save_stack+0x19/0x80
> [ 298.792544][T14664] ? path_mountpoint+0x2e0/0x2e0
> [ 298.793233][T14664] ? check_chain_key+0x236/0x5d0
> [ 298.793910][T14664] ? sched_clock_cpu+0x18/0x170
> [ 298.794527][T14664] ? find_held_lock+0x39/0x1d0
> [ 298.795153][T14664] do_filp_open+0x16a/0x260
> [ ... ]
>
> Fixes: 9fd4dcece43a ("debugfs: prevent access to possibly dead file_operations at file open")
> Reported-by: kbuild test robot <lkp@xxxxxxxxx>
> Signed-off-by: Taehee Yoo <ap420073@xxxxxxxxx>
> ---
>
> v1 -> v2:
> - Fix compile error
>
> fs/debugfs/file.c | 18 ++++++++++++++----
> 1 file changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
> index 634b09d18b77..e3075389fba0 100644
> --- a/fs/debugfs/file.c
> +++ b/fs/debugfs/file.c
> @@ -175,8 +175,13 @@ static int open_proxy_open(struct inode *inode, struct file *filp)
> if (r)
> goto out;
>
> - real_fops = fops_get(real_fops);
> - if (!real_fops) {
> + if (!fops_get(real_fops)) {
> +#ifdef MODULE
> + if (real_fops->owner &&
> + real_fops->owner->state == MODULE_STATE_GOING)
> + goto out;
> +#endif
Why is this in a #ifdef?
The real_fops->owner field will be present if MODULE is not enabled,
right? Shouldn't this just work the same for that case?
thanks,
greg k-h
