Re: [PATCH net v5] bonding: Fix out-of-bounds read in bond_option_arp_ip_targets_set()

[Jay Vosburgh <jay.vosburgh@canonical.com>]

'Simon Horman' <horms@kernel.org> wrote:

>From: Sam Sun <samsun1006219@gmail.com>
>
>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.
>
>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
>---[ end trace ]---
>
>Fix it by adding a check of string length before using it.
>
>Fixes: f9de11a16594 ("bonding: add ip checks when store ip target")
>Signed-off-by: Yue Sun <samsun1006219@gmail.com>
>Signed-off-by: Simon Horman <horms@kernel.org>

Acked-by: Jay Vosburgh <jay.vosburgh@canonical.com>

>---
>Changes in v5 (Simon):
>- Remove stray 'I4' from netdev_err() string. Thanks to Hangbin Liu.
>- Sorry for the long delay between v4 and v5, this completely slipped my
>  mind.
>- Link to v4: https://lore.kernel.org/r/20240419-bond-oob-v4-1-69dd1a66db20@kernel.org
>
>Changes in v4 (Simon):
>- Correct  whitespace mangled patch; posting as requested by Sam Sun
>- Link to v3: https://lore.kernel.org/r/CAEkJfYOnsLLiCrtgOpq2Upr+_W0dViYVHU8YdjJOi-mxD8H9oQ@mail.gmail.com
>
>Changes in v3 (Sam Sun):
>- According to Hangbin's opinion, change Fixes tag from 4fb0ef585eb2
>  ("bonding: convert arp_ip_target to use the new option API") to
>  f9de11a16594 ("bonding: add ip checks when store ip target").
>- Link to v2: https://lore.kernel.org/r/CAEkJfYMdDQKY1C-wBZLiaJ=dCqfM9r=rykwwf+J-XHsFp7D9Ag@mail.gmail.com/
>
>Changes in v2 (Sam Sun):
>- According to Jay and Hangbin's opinion, remove target address in
>  netdev_err message since target is not initialized in error path and
>  will not provide useful information.
>- Link to v1: https://lore.kernel.org/r/CAEkJfYPYF-nNB2oiXfXwjPG0VVB2Bd8Q8kAq+74J=R+4HkngWw@mail.gmail.com/
>---
> drivers/net/bonding/bond_options.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
>diff --git a/drivers/net/bonding/bond_options.c b/drivers/net/bonding/bond_options.c
>index 0cacd7027e35..228128e727c2 100644
>--- a/drivers/net/bonding/bond_options.c
>+++ b/drivers/net/bonding/bond_options.c
>@@ -1214,9 +1214,9 @@ 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)) {
>-			netdev_err(bond->dev, "invalid ARP target %pI4 specified\n",
>-				   &target);
>+		if (!(strlen(newval->string)) ||
>+		    !in4_pton(newval->string + 1, -1, (u8 *)&target, -1, NULL)) {
>+			netdev_err(bond->dev, "invalid ARP target specified\n");
> 			return ret;
> 		}
> 		if (newval->string[0] == '+')
>