Messages in this thread | | | Date | Wed, 8 Dec 2021 17:33:28 +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 11:29:47AM -0500, George Kennedy wrote: > > > On 12/8/2021 10:40 AM, Greg KH wrote: > > 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()? > tun_free_netdev() is called after err_free_flow has already done the free. > rtnl_lock() and rtnl_unlock() prevent the race.
Ok, good, it wasn't obvious from the context here.
> > Here is the full KASAN report: > > Syzkaller hit 'KASAN: invalid-free in selinux_tun_dev_free_security' bug. > > ================================================================== > 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 1.13.0-2.module+el8.3.0+7860+a7792d29 > 04/01/2014 > 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 > RIP: 0033:0x7fd496f4c289 > Code: 01 00 48 81 c4 80 00 00 00 e9 f1 fe ff ff 0f 1f 00 48 89 f8 48 89 f7 > 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff > 73 01 c3 48 8b 0d b7 db 2c 00 f7 d8 64 89 01 48 > RSP: 002b:00007fd497632e28 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 > RAX: ffffffffffffffda RBX: 0000000000603190 RCX: 00007fd496f4c289 > RDX: 0000000020000240 RSI: 00000000400454ca RDI: 0000000000000003 > RBP: 0000000000603198 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 000000000060319c > R13: 0000000000021000 R14: 0000000000000000 R15: 00007fd497633700 > </TASK> > > Allocated by task 25750: > kasan_save_stack+0x26/0x60 mm/kasan/common.c:38 > kasan_set_track mm/kasan/common.c:46 [inline] > set_alloc_info mm/kasan/common.c:434 [inline] > ____kasan_kmalloc mm/kasan/common.c:513 [inline] > __kasan_kmalloc+0x8d/0xb0 mm/kasan/common.c:522 > kasan_kmalloc include/linux/kasan.h:269 [inline] > kmem_cache_alloc_trace+0x18a/0x2d0 mm/slub.c:3261 > kmalloc include/linux/slab.h:590 [inline] > kzalloc include/linux/slab.h:724 [inline] > selinux_tun_dev_alloc_security+0x50/0x180 security/selinux/hooks.c:5594 > security_tun_dev_alloc_security+0x51/0xb0 security/security.c:2336 > tun_set_iff.constprop.66+0x107f/0x1d10 drivers/net/tun.c:2727 > __tun_chr_ioctl+0xdf8/0x2870 drivers/net/tun.c:3026 > 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 > > Freed by task 25750: > kasan_save_stack+0x26/0x60 mm/kasan/common.c:38 > kasan_set_track+0x25/0x30 mm/kasan/common.c:46 > kasan_set_free_info+0x24/0x40 mm/kasan/generic.c:370 > ____kasan_slab_free mm/kasan/common.c:366 [inline] > ____kasan_slab_free mm/kasan/common.c:328 [inline] > __kasan_slab_free+0xe8/0x120 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_set_iff.constprop.66+0x9f9/0x1d10 drivers/net/tun.c:2782 > __tun_chr_ioctl+0xdf8/0x2870 drivers/net/tun.c:3026 > 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 > > The buggy address belongs to the object at ffff888066b87370 > which belongs to the cache kmalloc-8 of size 8 > The buggy address is located 0 bytes inside of > 8-byte region [ffff888066b87370, ffff888066b87378) > The buggy address belongs to the page: > page:0000000003b0639d refcount:1 mapcount:0 mapping:0000000000000000 > index:0x0 pfn:0x66b87 > flags: 0xfffffc0000200(slab|node=0|zone=1|lastcpupid=0x1fffff) > raw: 000fffffc0000200 dead000000000100 dead000000000122 ffff888100042280 > raw: 0000000000000000 0000000080660066 00000001ffffffff 0000000000000000 > page dumped because: kasan: bad access detected > > Memory state around the buggy address: > ffff888066b87200: fc fb fc fc fc fc 00 fc fc fc fc fa fc fc fc fc > ffff888066b87280: fa fc fc fc fc fa fc fc fc fc fb fc fc fc fc fa > >ffff888066b87300: fc fc fc fc 00 fc fc fc fc fb fc fc fc fc fa fc > ^ > ffff888066b87380: fc fc fc fa fc fc fc fc 00 fc fc fc fc fa fc fc > ffff888066b87400: fc fc fa fc fc fc fc fa fc fc fc fc fa fc fc fc > ================================================================== > > > > > And why can't security_tun_dev_free_security() handle a NULL value? > > security_tun_dev_free_security() could be modified to handle the NULL value.
That's fine, most of this patch would still be needed even if you do that.
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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