Subject: Re: [PATCH net] drivers/net/bonding: Fix out-of-bounds read in bond_option_arp_ip_targets_set()

From: Jay Vosburgh <[email-masked]>
Date: Mon, 04 Mar 2024 18:47:04 -0800

Sam Sun <[email-masked]> wrote:

>Dear kernel developers and maintainers,
>
>We found a bug through our modified Syzkaller. In function
>bond_option_arp_ip_targets_set(), if newval->string is an empty
>string, newval->string+1 will point to the byte after the string,
>causing an out-of-bound read.  KASAN report is listed below.

	Conceptually, the change here seems fine.  However, I don't
think including the full KASAN report adds much to the description
above.

	Also, in the patch itself the line being added looks to have
been mangled (noted below).

>==================================================================
>BUG: KASAN: slab-out-of-bounds in strlen+0x7d/0xa0 lib/string.c:418
>Read of size 1 at addr ffff8881119c4781 by task syz-executor665/8107
>
>CPU: 1 PID: 8107 Comm: syz-executor665 Not tainted 6.7.0-rc7 #1
>Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
>Call Trace:
> <TASK>
> __dump_stack lib/dump_stack.c:88 [inline]
> dump_stack_lvl+0xd9/0x150 lib/dump_stack.c:106
> print_address_description mm/kasan/report.c:364 [inline]
> print_report+0xc1/0x5e0 mm/kasan/report.c:475
> kasan_report+0xbe/0xf0 mm/kasan/report.c:588
> strlen+0x7d/0xa0 lib/string.c:418
> __fortify_strlen include/linux/fortify-string.h:210 [inline]
> in4_pton+0xa3/0x3f0 net/core/utils.c:130
> bond_option_arp_ip_targets_set+0xc2/0x910
>drivers/net/bonding/bond_options.c:1201
> __bond_opt_set+0x2a4/0x1030 drivers/net/bonding/bond_options.c:767
> __bond_opt_set_notify+0x48/0x150 drivers/net/bonding/bond_options.c:792
> bond_opt_tryset_rtnl+0xda/0x160 drivers/net/bonding/bond_options.c:817
> bonding_sysfs_store_option+0xa1/0x120 drivers/net/bonding/bond_sysfs.c:156
> dev_attr_store+0x54/0x80 drivers/base/core.c:2366
> sysfs_kf_write+0x114/0x170 fs/sysfs/file.c:136
> kernfs_fop_write_iter+0x337/0x500 fs/kernfs/file.c:334
> call_write_iter include/linux/fs.h:2020 [inline]
> new_sync_write fs/read_write.c:491 [inline]
> vfs_write+0x96a/0xd80 fs/read_write.c:584
> ksys_write+0x122/0x250 fs/read_write.c:637
> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> do_syscall_64+0x40/0x110 arch/x86/entry/common.c:83
> entry_SYSCALL_64_after_hwframe+0x63/0x6b
>RIP: 0033:0x7f797835cfcd
>Code: 28 c3 e8 46 1e 00 00 66 0f 1f 44 00 00 f3 0f 1e fa 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 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
>RSP: 002b:00007ffff464ffb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
>RAX: ffffffffffffffda RBX: 00007ffff46501b8 RCX: 00007f797835cfcd
>RDX: 00000000000000f5 RSI: 0000000020000140 RDI: 0000000000000003
>RBP: 0000000000000001 R08: 0000000000000000 R09: 00007ffff46501b8
>R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
>R13: 00007ffff46501a8 R14: 00007f79783da530 R15: 0000000000000001
> </TASK>
>
>Allocated by task 8107:
> kasan_save_stack+0x22/0x40 mm/kasan/common.c:45
> kasan_set_track+0x25/0x30 mm/kasan/common.c:52
> ____kasan_kmalloc mm/kasan/common.c:374 [inline]
> ____kasan_kmalloc mm/kasan/common.c:333 [inline]
> __kasan_kmalloc+0xa3/0xb0 mm/kasan/common.c:383
> kasan_kmalloc include/linux/kasan.h:198 [inline]
> __do_kmalloc_node mm/slab_common.c:1007 [inline]
> __kmalloc_node_track_caller+0x5e/0xd0 mm/slab_common.c:1027
> kstrndup+0x72/0x110 mm/util.c:108
> bonding_sysfs_store_option+0x66/0x120 drivers/net/bonding/bond_sysfs.c:153
> dev_attr_store+0x54/0x80 drivers/base/core.c:2366
> sysfs_kf_write+0x114/0x170 fs/sysfs/file.c:136
> kernfs_fop_write_iter+0x337/0x500 fs/kernfs/file.c:334
> call_write_iter include/linux/fs.h:2020 [inline]
> new_sync_write fs/read_write.c:491 [inline]
> vfs_write+0x96a/0xd80 fs/read_write.c:584
> ksys_write+0x122/0x250 fs/read_write.c:637
> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> do_syscall_64+0x40/0x110 arch/x86/entry/common.c:83
> entry_SYSCALL_64_after_hwframe+0x63/0x6b
>
>The buggy address belongs to the object at ffff8881119c4780
> which belongs to the cache kmalloc-32 of size 32
>The buggy address is located 0 bytes to the right of
> allocated 1-byte region [ffff8881119c4780, ffff8881119c4781)
>
>The buggy address belongs to the physical page:
>page:ffffea0004467100 refcount:1 mapcount:0 mapping:0000000000000000
>index:0xffff8881119c4fc1 pfn:0x1119c4
>flags: 0x57ff00000000800(slab|node=1|zone=2|lastcpupid=0x7ff)
>page_type: 0x3f()
>raw: 057ff00000000800 ffff888013040100 ffffea000405a650 ffffea0004156b90
>raw: ffff8881119c4fc1 ffff8881119c4000 000000010000003f 0000000000000000
>page dumped because: kasan: bad access detected
>page_owner tracks the page as allocated
>page last allocated via order 0, migratetype Unmovable, gfp_mask
>0x2420c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_COMP|__GFP_THISNODE),
>pid 25, tgid 25 (kworker/u6:0), ts 73787966798, free_ts 73774684635
> set_page_owner include/linux/page_owner.h:31 [inline]
> post_alloc_hook+0x2d9/0x350 mm/page_alloc.c:1537
> prep_new_page mm/page_alloc.c:1544 [inline]
> get_page_from_freelist+0xd38/0x2fa0 mm/page_alloc.c:3312
> __alloc_pages+0x21d/0x21f0 mm/page_alloc.c:4568
> __alloc_pages_node include/linux/gfp.h:238 [inline]
> kmem_getpages mm/slab.c:1356 [inline]
> cache_grow_begin+0x9b/0x3c0 mm/slab.c:2550
> cache_alloc_refill+0x289/0x3a0 mm/slab.c:2923
> ____cache_alloc mm/slab.c:2999 [inline]
> ____cache_alloc mm/slab.c:2982 [inline]
> __do_cache_alloc mm/slab.c:3185 [inline]
> slab_alloc_node mm/slab.c:3230 [inline]
> __kmem_cache_alloc_node+0x374/0x420 mm/slab.c:3521
> __do_kmalloc_node mm/slab_common.c:1006 [inline]
> __kmalloc_node+0x50/0xd0 mm/slab_common.c:1014
> kmalloc_array_node include/linux/slab.h:698 [inline]
> kcalloc_node include/linux/slab.h:703 [inline]
> memcg_alloc_slab_cgroups+0x10e/0x210 mm/memcontrol.c:2968
> account_slab mm/slab.h:637 [inline]
> kmem_getpages mm/slab.c:1364 [inline]
> cache_grow_begin+0x349/0x3c0 mm/slab.c:2550
> cache_alloc_refill+0x289/0x3a0 mm/slab.c:2923
> ____cache_alloc mm/slab.c:2999 [inline]
> ____cache_alloc mm/slab.c:2982 [inline]
> __do_cache_alloc mm/slab.c:3182 [inline]
> slab_alloc_node mm/slab.c:3230 [inline]
> kmem_cache_alloc_node+0x3e1/0x4a0 mm/slab.c:3509
> alloc_task_struct_node kernel/fork.c:173 [inline]
> dup_task_struct kernel/fork.c:1110 [inline]
> copy_process+0x3f6/0x73e0 kernel/fork.c:2332
> kernel_clone+0xeb/0x8c0 kernel/fork.c:2907
> user_mode_thread+0xb4/0xf0 kernel/fork.c:2985
> call_usermodehelper_exec_work kernel/umh.c:172 [inline]
> call_usermodehelper_exec_work+0xd0/0x180 kernel/umh.c:158
> process_one_work+0x878/0x15c0 kernel/workqueue.c:2627
>page last free stack trace:
> reset_page_owner include/linux/page_owner.h:24 [inline]
> free_pages_prepare mm/page_alloc.c:1137 [inline]
> free_unref_page_prepare+0x4c5/0xa60 mm/page_alloc.c:2347
> free_unref_page+0x33/0x3d0 mm/page_alloc.c:2487
> rcu_do_batch kernel/rcu/tree.c:2158 [inline]
> rcu_core+0x817/0x1670 kernel/rcu/tree.c:2431
> __do_softirq+0x1d4/0x85e kernel/softirq.c:553
>
>Memory state around the buggy address:
> ffff8881119c4680: fa fb fb fb fc fc fc fc 00 01 fc fc fc fc fc fc
> ffff8881119c4700: 00 05 fc fc fc fc fc fc 00 00 00 fc fc fc fc fc
>>ffff8881119c4780: 01 fc fc fc fc fc fc fc fb fb fb fb fc fc fc fc
>                   ^
> ffff8881119c4800: 00 01 fc fc fc fc fc fc fb fb fb fb fc fc fc fc
> ffff8881119c4880: 00 fc fc fc fc fc fc fc 00 01 fc fc fc fc fc fc
>==================================================================
>
>We developed a patch to fix this problem. Check the string length
>first before calling in4_pton().
>
>Reported-by: Yue Sun <[email-masked]>
>Signed-off-by: Yue Sun <[email-masked]>
>
>diff --git a/drivers/net/bonding/bond_options.c
>b/drivers/net/bonding/bond_options.c
>index f3f27f0bd2a6..a6d01055f455 100644
>--- a/drivers/net/bonding/bond_options.c
>+++ b/drivers/net/bonding/bond_options.c
>@@ -1198,7 +1198,7 @@ static int bond_option_arp_ip_targets_set(struct
>bonding *bond,
>     __be32 target;
>
>     if (newval->string) {
>-        if (!in4_pton(newval->string+1, -1, (u8 *)&target, -1, NULL)) {
>+        if (!strlen(newval->string) || !in4_pton(newval->string+1,
>-1, (u8 *)&target, -1, NULL)) {

	The text beginning with "-1," is a separate line, and something
messed up the tabs.  Also, this should be rewritten as

		if (!strlen(newval->string) ||
		    !in4_pton(newval->string + 1, -1, (u8 *)&target, -1, NULL)) {

	to avoid a long line.

	-J

>             netdev_err(bond->dev, "invalid ARP target %pI4 specified\n",
>                    &target);
>             return ret;
>

---
	-Jay Vosburgh, [email-masked]