From: Jann Horn <jannh@xxxxxxxxxx>
[ Upstream commit 6ab405114b0b229151ef06f4e31c7834dd09d0c0 ]
Check whether inputs from userspace are too long (explicit length field too
big or string not null-terminated) to avoid out-of-bounds reads.
As far as I can tell, this can at worst lead to very limited kernel heap
memory disclosure or oopses.
This bug can be triggered by an unprivileged user even if the xt_bpf module
is not loaded: iptables is available in network namespaces, and the xt_bpf
module can be autoloaded.
Triggering the bug with a classic BPF filter with fake length 0x1000 causes
the following KASAN report:
==================================================================
BUG: KASAN: slab-out-of-bounds in bpf_prog_create+0x84/0xf0
Read of size 32768 at addr ffff8801eff2c494 by task test/4627
CPU: 0 PID: 4627 Comm: test Not tainted 4.15.0-rc1+ #1
[...]
Call Trace:
dump_stack+0x5c/0x85
print_address_description+0x6a/0x260
kasan_report+0x254/0x370
? bpf_prog_create+0x84/0xf0
memcpy+0x1f/0x50
bpf_prog_create+0x84/0xf0
bpf_mt_check+0x90/0xd6 [xt_bpf]
[...]
Allocated by task 4627:
kasan_kmalloc+0xa0/0xd0
__kmalloc_node+0x47/0x60
xt_alloc_table_info+0x41/0x70 [x_tables]
[...]
The buggy address belongs to the object at ffff8801eff2c3c0
which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 212 bytes inside of
2048-byte region [ffff8801eff2c3c0, ffff8801eff2cbc0)
[...]
==================================================================
Fixes: e6f30c731718 ("netfilter: x_tables: add xt_bpf match")
Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Signed-off-by: Zubin Mithra <zsm@xxxxxxxxxxxx>
---
* Syzkaller triggered an OOB read with the following stacktrace:
__dump_stack lib/dump_stack.c:15 [inline]
dump_stack+0xcb/0x130 lib/dump_stack.c:56
print_trailer+0x151/0x15a mm/slub.c:658
object_err+0x35/0x3d mm/slub.c:665
print_address_description mm/kasan/report.c:188 [inline]
kasan_report_error mm/kasan/report.c:285 [inline]
kasan_report.part.0.cold+0x21a/0x4c1 mm/kasan/report.c:310
kasan_report+0x25/0x30 mm/kasan/report.c:297
check_memory_region_inline mm/kasan/kasan.c:292 [inline]
check_memory_region+0x116/0x190 mm/kasan/kasan.c:299
memcpy+0x24/0x50 mm/kasan/kasan.c:334
bpf_prog_create+0xdd/0x230 net/core/filter.c:1075
bpf_mt_check+0xb1/0x100 net/netfilter/xt_bpf.c:31
xt_check_match+0x26b/0x560 net/netfilter/x_tables.c:444
check_match net/ipv4/netfilter/ip_tables.c:593 [inline]
find_check_match net/ipv4/netfilter/ip_tables.c:616 [inline]
find_check_entry.isra.0+0x2fe/0x950 net/ipv4/netfilter/ip_tables.c:673
translate_table+0xb3f/0x15b0 net/ipv4/netfilter/ip_tables.c:878
do_replace net/ipv4/netfilter/ip_tables.c:1300 [inline]
do_ipt_set_ctl+0x2cf/0x460 net/ipv4/netfilter/ip_tables.c:1864
nf_sockopt net/netfilter/nf_sockopt.c:105 [inline]
nf_setsockopt+0x72/0xd0 net/netfilter/nf_sockopt.c:114
ip_setsockopt net/ipv4/ip_sockglue.c:1227 [inline]
ip_setsockopt+0xa0/0xb0 net/ipv4/ip_sockglue.c:1212
udp_setsockopt+0x53/0x90 net/ipv4/udp.c:2162
sock_common_setsockopt+0x9f/0xe0 net/core/sock.c:2697
SYSC_setsockopt net/socket.c:1769 [inline]
SyS_setsockopt+0x146/0x210 net/socket.c:1748
entry_SYSCALL_64_fastpath+0x1e/0xa0
* This commit is present in linux-4.14.y.
* This patch resolves conflicts that arise due to the following commit
not being present in linux-4.9.y, linux-4.4.y:
- 2c16d6033264 ("netfilter: xt_bpf: support ebpf")
* Tests run: syzkaller reproducer
net/netfilter/xt_bpf.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/net/netfilter/xt_bpf.c b/net/netfilter/xt_bpf.c
index dffee9d47ec4b..7b993f25aab92 100644
--- a/net/netfilter/xt_bpf.c
+++ b/net/netfilter/xt_bpf.c
@@ -25,6 +25,9 @@ static int bpf_mt_check(const struct xt_mtchk_param *par)
struct xt_bpf_info *info = par->matchinfo;
struct sock_fprog_kern program;
+ if (info->bpf_program_num_elem > XT_BPF_MAX_NUM_INSTR)
+ return -EINVAL;
+
program.len = info->bpf_program_num_elem;
program.filter = info->bpf_program;
--
2.25.0.265.gbab2e86ba0-goog
