Messages in this thread | | | Date | Wed, 8 Dec 2021 16:40:44 +0100 | From | Greg KH <> | Subject | Re: [PATCH] tun: avoid double free in tun_free_netdev |
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On Wed, Dec 08, 2021 at 09:43:25AM -0500, George Kennedy wrote: > Avoid double free in tun_free_netdev() by clearing tun->security > after free and using it to indicate that free has already been done. > > BUG: KASAN: double-free or invalid-free in selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605 > > CPU: 0 PID: 25750 Comm: syz-executor416 Not tainted 5.16.0-rc2-syzk #1 > Hardware name: Red Hat KVM, BIOS > Call Trace: > <TASK> > __dump_stack lib/dump_stack.c:88 [inline] > dump_stack_lvl+0x89/0xb5 lib/dump_stack.c:106 > print_address_description.constprop.9+0x28/0x160 mm/kasan/report.c:247 > kasan_report_invalid_free+0x55/0x80 mm/kasan/report.c:372 > ____kasan_slab_free mm/kasan/common.c:346 [inline] > __kasan_slab_free+0x107/0x120 mm/kasan/common.c:374 > kasan_slab_free include/linux/kasan.h:235 [inline] > slab_free_hook mm/slub.c:1723 [inline] > slab_free_freelist_hook mm/slub.c:1749 [inline] > slab_free mm/slub.c:3513 [inline] > kfree+0xac/0x2d0 mm/slub.c:4561 > selinux_tun_dev_free_security+0x1a/0x20 security/selinux/hooks.c:5605 > security_tun_dev_free_security+0x4f/0x90 security/security.c:2342 > tun_free_netdev+0xe6/0x150 drivers/net/tun.c:2215 > netdev_run_todo+0x4df/0x840 net/core/dev.c:10627 > rtnl_unlock+0x13/0x20 net/core/rtnetlink.c:112 > __tun_chr_ioctl+0x80c/0x2870 drivers/net/tun.c:3302 > tun_chr_ioctl+0x2f/0x40 drivers/net/tun.c:3311 > vfs_ioctl fs/ioctl.c:51 [inline] > __do_sys_ioctl fs/ioctl.c:874 [inline] > __se_sys_ioctl fs/ioctl.c:860 [inline] > __x64_sys_ioctl+0x19d/0x220 fs/ioctl.c:860 > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > do_syscall_64+0x3a/0x80 arch/x86/entry/common.c:80 > entry_SYSCALL_64_after_hwframe+0x44/0xae > > Reported-by: syzkaller <syzkaller@googlegroups.com> > Signed-off-by: George Kennedy <george.kennedy@oracle.com> > --- > drivers/net/tun.c | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > index 1572878..617c71f 100644 > --- a/drivers/net/tun.c > +++ b/drivers/net/tun.c > @@ -2212,7 +2212,10 @@ static void tun_free_netdev(struct net_device *dev) > dev->tstats = NULL; > > tun_flow_uninit(tun); > - security_tun_dev_free_security(tun->security); > + if (tun->security) { > + security_tun_dev_free_security(tun->security); > + tun->security = NULL; > + } > __tun_set_ebpf(tun, &tun->steering_prog, NULL); > __tun_set_ebpf(tun, &tun->filter_prog, NULL); > } > @@ -2779,7 +2782,11 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr) > > err_free_flow: > tun_flow_uninit(tun); > - security_tun_dev_free_security(tun->security); > + if (tun->security) { > + security_tun_dev_free_security(tun->security); > + /* Let tun_free_netdev() know the free has already been done. */ > + tun->security = NULL;
What protects this from racing with tun_free_netdev()?
And why can't security_tun_dev_free_security() handle a NULL value?
thanks,
greg k-h
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