Element replace (with a socket different from the one stored) may race
with socket's close() link popping & unlinking. __sock_map_delete()
unconditionally unrefs the (wrong) element:
// set map[0] = s0
map_update_elem(map, 0, s0)
// drop fd of s0
close(s0)
sock_map_close()
lock_sock(sk) (s0!)
sock_map_remove_links(sk)
link = sk_psock_link_pop()
sock_map_unlink(sk, link)
sock_map_delete_from_link
// replace map[0] with s1
map_update_elem(map, 0, s1)
sock_map_update_elem
(s1!) lock_sock(sk)
sock_map_update_common
psock = sk_psock(sk)
spin_lock(&stab->lock)
osk = stab->sks[idx]
sock_map_add_link(..., &stab->sks[idx])
sock_map_unref(osk, &stab->sks[idx])
psock = sk_psock(osk)
sk_psock_put(sk, psock)
if (refcount_dec_and_test(&psock))
sk_psock_drop(sk, psock)
spin_unlock(&stab->lock)
unlock_sock(sk)
__sock_map_delete
spin_lock(&stab->lock)
sk = *psk // s1 replaced s0; sk == s1
if (!sk_test || sk_test == sk) // sk_test (s0) != sk (s1); no branch
sk = xchg(psk, NULL)
if (sk)
sock_map_unref(sk, psk) // unref s1; sks[idx] will dangle
psock = sk_psock(sk)
sk_psock_put(sk, psock)
if (refcount_dec_and_test())
sk_psock_drop(sk, psock)
spin_unlock(&stab->lock)
release_sock(sk)
Then close(map) enqueues bpf_map_free_deferred, which finally calls
sock_map_free(). This results in some refcount_t warnings along with
a KASAN splat [1].
Fix __sock_map_delete(), do not allow sock_map_unref() on elements that
may have been replaced.
[1]:
BUG: KASAN: slab-use-after-free in sock_map_free+0x10e/0x330
Write of size 4 at addr ffff88811f5b9100 by task kworker/u64:12/1063
CPU: 14 UID: 0 PID: 1063 Comm: kworker/u64:12 Not tainted 6.12.0+ #125
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.3-1-1 04/01/2014
Workqueue: events_unbound bpf_map_free_deferred
Call Trace:
<TASK>
dump_stack_lvl+0x68/0x90
print_report+0x174/0x4f6
kasan_report+0xb9/0x190
kasan_check_range+0x10f/0x1e0
sock_map_free+0x10e/0x330
bpf_map_free_deferred+0x173/0x320
process_one_work+0x846/0x1420
worker_thread+0x5b3/0xf80
kthread+0x29e/0x360
ret_from_fork+0x2d/0x70
ret_from_fork_asm+0x1a/0x30
</TASK>
Allocated by task 1202:
kasan_save_stack+0x1e/0x40
kasan_save_track+0x10/0x30
__kasan_slab_alloc+0x85/0x90
kmem_cache_alloc_noprof+0x131/0x450
sk_prot_alloc+0x5b/0x220
sk_alloc+0x2c/0x870
unix_create1+0x88/0x8a0
unix_create+0xc5/0x180
__sock_create+0x241/0x650
__sys_socketpair+0x1ce/0x420
__x64_sys_socketpair+0x92/0x100
do_syscall_64+0x93/0x180
entry_SYSCALL_64_after_hwframe+0x76/0x7e
Freed by task 46:
kasan_save_stack+0x1e/0x40
kasan_save_track+0x10/0x30
kasan_save_free_info+0x37/0x60
__kasan_slab_free+0x4b/0x70
kmem_cache_free+0x1a1/0x590
__sk_destruct+0x388/0x5a0
sk_psock_destroy+0x73e/0xa50
process_one_work+0x846/0x1420
worker_thread+0x5b3/0xf80
kthread+0x29e/0x360
ret_from_fork+0x2d/0x70
ret_from_fork_asm+0x1a/0x30
The buggy address belongs to the object at ffff88811f5b9080
which belongs to the cache UNIX-STREAM of size 1984
The buggy address is located 128 bytes inside of
freed 1984-byte region [ffff88811f5b9080, ffff88811f5b9840)
The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x11f5b8
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:ffff888127d49401
flags: 0x17ffffc0000040(head|node=0|zone=2|lastcpupid=0x1fffff)
page_type: f5(slab)
raw: 0017ffffc0000040 ffff8881042e4500 dead000000000122 0000000000000000
raw: 0000000000000000 00000000800f000f 00000001f5000000 ffff888127d49401
head: 0017ffffc0000040 ffff8881042e4500 dead000000000122 0000000000000000
head: 0000000000000000 00000000800f000f 00000001f5000000 ffff888127d49401
head: 0017ffffc0000003 ffffea00047d6e01 ffffffffffffffff 0000000000000000
head: 0000000000000008 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
Memory state around the buggy address:
ffff88811f5b9000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88811f5b9080: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88811f5b9180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88811f5b9200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
Disabling lock debugging due to kernel taint
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 14 PID: 1063 at lib/refcount.c:25 refcount_warn_saturate+0xce/0x150
CPU: 14 UID: 0 PID: 1063 Comm: kworker/u64:12 Tainted: G B 6.12.0+ #125
Tainted: [B]=BAD_PAGE
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.3-1-1 04/01/2014
Workqueue: events_unbound bpf_map_free_deferred
RIP: 0010:refcount_warn_saturate+0xce/0x150
Code: 34 73 eb 03 01 e8 82 53 ad fe 0f 0b eb b1 80 3d 27 73 eb 03 00 75 a8 48 c7 c7 80 bd 95 84 c6 05 17 73 eb 03 01 e8 62 53 ad fe <0f> 0b eb 91 80 3d 06 73 eb 03 00 75 88 48 c7 c7 e0 bd 95 84 c6 05
RSP: 0018:ffff88815c49fc70 EFLAGS: 00010282
RAX: 0000000000000000 RBX: ffff88811f5b9100 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000001
RBP: 0000000000000002 R08: 0000000000000001 R09: ffffed10bcde6349
R10: ffff8885e6f31a4b R11: 0000000000000000 R12: ffff88813be0b000
R13: ffff88811f5b9100 R14: ffff88811f5b9080 R15: ffff88813be0b024
FS: 0000000000000000(0000) GS:ffff8885e6f00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055dda99b0250 CR3: 000000015dbac000 CR4: 0000000000752ef0
PKRU: 55555554
Call Trace:
<TASK>
? __warn.cold+0x5f/0x1ff
? refcount_warn_saturate+0xce/0x150
? report_bug+0x1ec/0x390
? handle_bug+0x58/0x90
? exc_invalid_op+0x13/0x40
? asm_exc_invalid_op+0x16/0x20
? refcount_warn_saturate+0xce/0x150
sock_map_free+0x2e5/0x330
bpf_map_free_deferred+0x173/0x320
process_one_work+0x846/0x1420
worker_thread+0x5b3/0xf80
kthread+0x29e/0x360
ret_from_fork+0x2d/0x70
ret_from_fork_asm+0x1a/0x30
</TASK>
irq event stamp: 10741
hardirqs last enabled at (10741): [<ffffffff84400ec6>] asm_sysvec_apic_timer_interrupt+0x16/0x20
hardirqs last disabled at (10740): [<ffffffff811e532d>] handle_softirqs+0x60d/0x770
softirqs last enabled at (10506): [<ffffffff811e55a9>] __irq_exit_rcu+0x109/0x210
softirqs last disabled at (10301): [<ffffffff811e55a9>] __irq_exit_rcu+0x109/0x210
refcount_t: underflow; use-after-free.
WARNING: CPU: 14 PID: 1063 at lib/refcount.c:28 refcount_warn_saturate+0xee/0x150
CPU: 14 UID: 0 PID: 1063 Comm: kworker/u64:12 Tainted: G B W 6.12.0+ #125
Tainted: [B]=BAD_PAGE, [W]=WARN
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.3-1-1 04/01/2014
Workqueue: events_unbound bpf_map_free_deferred
RIP: 0010:refcount_warn_saturate+0xee/0x150
Code: 17 73 eb 03 01 e8 62 53 ad fe 0f 0b eb 91 80 3d 06 73 eb 03 00 75 88 48 c7 c7 e0 bd 95 84 c6 05 f6 72 eb 03 01 e8 42 53 ad fe <0f> 0b e9 6e ff ff ff 80 3d e6 72 eb 03 00 0f 85 61 ff ff ff 48 c7
RSP: 0018:ffff88815c49fc70 EFLAGS: 00010282
RAX: 0000000000000000 RBX: ffff88811f5b9100 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000001
RBP: 0000000000000003 R08: 0000000000000001 R09: ffffed10bcde6349
R10: ffff8885e6f31a4b R11: 0000000000000000 R12: ffff88813be0b000
R13: ffff88811f5b9100 R14: ffff88811f5b9080 R15: ffff88813be0b024
FS: 0000000000000000(0000) GS:ffff8885e6f00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055dda99b0250 CR3: 000000015dbac000 CR4: 0000000000752ef0
PKRU: 55555554
Call Trace:
<TASK>
? __warn.cold+0x5f/0x1ff
? refcount_warn_saturate+0xee/0x150
? report_bug+0x1ec/0x390
? handle_bug+0x58/0x90
? exc_invalid_op+0x13/0x40
? asm_exc_invalid_op+0x16/0x20
? refcount_warn_saturate+0xee/0x150
sock_map_free+0x2d3/0x330
bpf_map_free_deferred+0x173/0x320
process_one_work+0x846/0x1420
worker_thread+0x5b3/0xf80
kthread+0x29e/0x360
ret_from_fork+0x2d/0x70
ret_from_fork_asm+0x1a/0x30
</TASK>
irq event stamp: 10741
hardirqs last enabled at (10741): [<ffffffff84400ec6>] asm_sysvec_apic_timer_interrupt+0x16/0x20
hardirqs last disabled at (10740): [<ffffffff811e532d>] handle_softirqs+0x60d/0x770
softirqs last enabled at (10506): [<ffffffff811e55a9>] __irq_exit_rcu+0x109/0x210
softirqs last disabled at (10301): [<ffffffff811e55a9>] __irq_exit_rcu+0x109/0x210
Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
Signed-off-by: Michal Luczaj <mhal@xxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Reviewed-by: John Fastabend <john.fastabend@xxxxxxxxx>
Link: https://lore.kernel.org/bpf/20241202-sockmap-replace-v1-3-1e88579e7bd5@xxxxxxx
diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index 20b348b1964a..f1b9b3958792 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -412,12 +412,11 @@ static void *sock_map_lookup_sys(struct bpf_map *map, void *key)
static int __sock_map_delete(struct bpf_stab *stab, struct sock *sk_test,
struct sock **psk)
{
- struct sock *sk;
+ struct sock *sk = NULL;
int err = 0;
spin_lock_bh(&stab->lock);
- sk = *psk;
- if (!sk_test || sk_test == sk)
+ if (!sk_test || sk_test == *psk)
sk = xchg(psk, NULL);
if (likely(sk))
