[PATCH v2 bpf 0/2] bpf: fix OOB accesses in map_delete_elem callbacks

[PATCH v2 bpf 0/2] bpf: fix OOB accesses in map_delete_elem callbacks

[Maciej Fijalkowski]

v1->v2:
- CC stable and collect tags from Toke & John

Hi,

Jordy reported that for big enough XSKMAPs and DEVMAPs, when deleting
elements, OOB writes occur.

Reproducer below:

// compile with gcc -o map_poc map_poc.c -lbpf
#include <errno.h>
#include <linux/bpf.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/syscall.h>
#include <unistd.h>


int main() {
  // Create a large enough BPF XSK map
  int map_fd;
  union bpf_attr create_attr = {
      .map_type = BPF_MAP_TYPE_XSKMAP,
      .key_size = sizeof(int),
      .value_size = sizeof(int),
      .max_entries = 0x80000000 + 2,
  };

  map_fd = syscall(SYS_bpf, BPF_MAP_CREATE, &create_attr, sizeof(create_attr));
  if (map_fd < 0) {
    fprintf(stderr, "Failed to create BPF map: %s\n", strerror(errno));
    return 1;
  }


  // Delete an element from the map using syscall
  unsigned int key = 0x80000000 + 1;
  if (syscall(SYS_bpf, BPF_MAP_DELETE_ELEM,
              &(union bpf_attr){
                  .map_fd = map_fd,
                  .key = &key,
              },
              sizeof(union bpf_attr)) < 0) {
    fprintf(stderr, "Failed to delete element from BPF map: %s\n",
            strerror(errno));
    return 1;
  }

  close(map_fd);
  return 0;
}

This tiny series changes data types from int to u32 of keys being used
for map accesses.

Thanks,
Maciej


Maciej Fijalkowski (2):
  xsk: fix OOB map writes when deleting elements
  bpf: fix OOB devmap writes when deleting elements

 kernel/bpf/devmap.c | 6 +++---
 net/xdp/xskmap.c    | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

-- 
2.34.1

[PATCH v2 bpf 1/2] xsk: fix OOB map writes when deleting elements

[Maciej Fijalkowski]

Jordy says:

"
In the xsk_map_delete_elem function an unsigned integer
(map->max_entries) is compared with a user-controlled signed integer
(k). Due to implicit type conversion, a large unsigned value for
map->max_entries can bypass the intended bounds check:

	if (k >= map->max_entries)
		return -EINVAL;

This allows k to hold a negative value (between -2147483648 and -2),
which is then used as an array index in m->xsk_map[k], which results
in an out-of-bounds access.

	spin_lock_bh(&m->lock);
	map_entry = &m->xsk_map[k]; // Out-of-bounds map_entry
	old_xs = unrcu_pointer(xchg(map_entry, NULL));  // Oob write
	if (old_xs)
		xsk_map_sock_delete(old_xs, map_entry);
	spin_unlock_bh(&m->lock);

The xchg operation can then be used to cause an out-of-bounds write.
Moreover, the invalid map_entry passed to xsk_map_sock_delete can lead
to further memory corruption.
"

It indeed results in following splat:

[76612.897343] BUG: unable to handle page fault for address: ffffc8fc2e461108
[76612.904330] #PF: supervisor write access in kernel mode
[76612.909639] #PF: error_code(0x0002) - not-present page
[76612.914855] PGD 0 P4D 0
[76612.917431] Oops: Oops: 0002 [#1] PREEMPT SMP
[76612.921859] CPU: 11 UID: 0 PID: 10318 Comm: a.out Not tainted 6.12.0-rc1+ #470
[76612.929189] Hardware name: Intel Corporation S2600WFT/S2600WFT, BIOS SE5C620.86B.02.01.0008.031920191559 03/19/2019
[76612.939781] RIP: 0010:xsk_map_delete_elem+0x2d/0x60
[76612.944738] Code: 00 00 41 54 55 53 48 63 2e 3b 6f 24 73 38 4c 8d a7 f8 00 00 00 48 89 fb 4c 89 e7 e8 2d bf 05 00 48 8d b4 eb 00 01 00 00 31 ff <48> 87 3e 48 85 ff 74 05 e8 16 ff ff ff 4c 89 e7 e8 3e bc 05 00 31
[76612.963774] RSP: 0018:ffffc9002e407df8 EFLAGS: 00010246
[76612.969079] RAX: 0000000000000000 RBX: ffffc9002e461000 RCX: 0000000000000000
[76612.976323] RDX: 0000000000000001 RSI: ffffc8fc2e461108 RDI: 0000000000000000
[76612.983569] RBP: ffffffff80000001 R08: 0000000000000000 R09: 0000000000000007
[76612.990812] R10: ffffc9002e407e18 R11: ffff888108a38858 R12: ffffc9002e4610f8
[76612.998060] R13: ffff888108a38858 R14: 00007ffd1ae0ac78 R15: ffffc9002e4610c0
[76613.005303] FS:  00007f80b6f59740(0000) GS:ffff8897e0ec0000(0000) knlGS:0000000000000000
[76613.013517] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[76613.019349] CR2: ffffc8fc2e461108 CR3: 000000011e3ef001 CR4: 00000000007726f0
[76613.026595] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[76613.033841] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[76613.041086] PKRU: 55555554
[76613.043842] Call Trace:
[76613.046331]  <TASK>
[76613.048468]  ? __die+0x20/0x60
[76613.051581]  ? page_fault_oops+0x15a/0x450
[76613.055747]  ? search_extable+0x22/0x30
[76613.059649]  ? search_bpf_extables+0x5f/0x80
[76613.063988]  ? exc_page_fault+0xa9/0x140
[76613.067975]  ? asm_exc_page_fault+0x22/0x30
[76613.072229]  ? xsk_map_delete_elem+0x2d/0x60
[76613.076573]  ? xsk_map_delete_elem+0x23/0x60
[76613.080914]  __sys_bpf+0x19b7/0x23c0
[76613.084555]  __x64_sys_bpf+0x1a/0x20
[76613.088194]  do_syscall_64+0x37/0xb0
[76613.091832]  entry_SYSCALL_64_after_hwframe+0x4b/0x53
[76613.096962] RIP: 0033:0x7f80b6d1e88d
[76613.100592] Code: 5b 41 5c c3 66 0f 1f 84 00 00 00 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 8b 0d 73 b5 0f 00 f7 d8 64 89 01 48
[76613.119631] RSP: 002b:00007ffd1ae0ac68 EFLAGS: 00000206 ORIG_RAX: 0000000000000141
[76613.131330] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f80b6d1e88d
[76613.142632] RDX: 0000000000000098 RSI: 00007ffd1ae0ad20 RDI: 0000000000000003
[76613.153967] RBP: 00007ffd1ae0adc0 R08: 0000000000000000 R09: 0000000000000000
[76613.166030] R10: 00007f80b6f77040 R11: 0000000000000206 R12: 00007ffd1ae0aed8
[76613.177130] R13: 000055ddf42ce1e9 R14: 000055ddf42d0d98 R15: 00007f80b6fab040
[76613.188129]  </TASK>

Fix this by simply changing key type from int to u32.

Fixes: fbfc504a24f5 ("bpf: introduce new bpf AF_XDP map type BPF_MAP_TYPE_XSKMAP")
CC: stable@vger.kernel.org
Reported-by: Jordy Zomer <jordyzomer@google.com>
Suggested-by: Jordy Zomer <jordyzomer@google.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
---
 net/xdp/xskmap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/xdp/xskmap.c b/net/xdp/xskmap.c
index e1c526f97ce3..afa457506274 100644
--- a/net/xdp/xskmap.c
+++ b/net/xdp/xskmap.c
@@ -224,7 +224,7 @@ static long xsk_map_delete_elem(struct bpf_map *map, void *key)
 	struct xsk_map *m = container_of(map, struct xsk_map, map);
 	struct xdp_sock __rcu **map_entry;
 	struct xdp_sock *old_xs;
-	int k = *(u32 *)key;
+	u32 k = *(u32 *)key;
 
 	if (k >= map->max_entries)
 		return -EINVAL;
-- 
2.34.1

[PATCH v2 bpf 2/2] bpf: fix OOB devmap writes when deleting elements

[Maciej Fijalkowski]

Jordy reported issue against XSKMAP which also applies to DEVMAP - the
index used for accessing map entry, due to being a signed integer,
causes the OOB writes. Fix is simple as changing the type from int to
u32, however, when compared to XSKMAP case, one more thing needs to be
addressed.

When map is released from system via dev_map_free(), we iterate through
all of the entries and an iterator variable is also an int, which
implies OOB accesses. Again, change it to be u32.

Example splat below:

[  160.724676] BUG: unable to handle page fault for address: ffffc8fc2c001000
[  160.731662] #PF: supervisor read access in kernel mode
[  160.736876] #PF: error_code(0x0000) - not-present page
[  160.742095] PGD 0 P4D 0
[  160.744678] Oops: Oops: 0000 [#1] PREEMPT SMP
[  160.749106] CPU: 1 UID: 0 PID: 520 Comm: kworker/u145:12 Not tainted 6.12.0-rc1+ #487
[  160.757050] Hardware name: Intel Corporation S2600WFT/S2600WFT, BIOS SE5C620.86B.02.01.0008.031920191559 03/19/2019
[  160.767642] Workqueue: events_unbound bpf_map_free_deferred
[  160.773308] RIP: 0010:dev_map_free+0x77/0x170
[  160.777735] Code: 00 e8 fd 91 ed ff e8 b8 73 ed ff 41 83 7d 18 19 74 6e 41 8b 45 24 49 8b bd f8 00 00 00 31 db 85 c0 74 48 48 63 c3 48 8d 04 c7 <48> 8b 28 48 85 ed 74 30 48 8b 7d 18 48 85 ff 74 05 e8 b3 52 fa ff
[  160.796777] RSP: 0018:ffffc9000ee1fe38 EFLAGS: 00010202
[  160.802086] RAX: ffffc8fc2c001000 RBX: 0000000080000000 RCX: 0000000000000024
[  160.809331] RDX: 0000000000000000 RSI: 0000000000000024 RDI: ffffc9002c001000
[  160.816576] RBP: 0000000000000000 R08: 0000000000000023 R09: 0000000000000001
[  160.823823] R10: 0000000000000001 R11: 00000000000ee6b2 R12: dead000000000122
[  160.831066] R13: ffff88810c928e00 R14: ffff8881002df405 R15: 0000000000000000
[  160.838310] FS:  0000000000000000(0000) GS:ffff8897e0c40000(0000) knlGS:0000000000000000
[  160.846528] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  160.852357] CR2: ffffc8fc2c001000 CR3: 0000000005c32006 CR4: 00000000007726f0
[  160.859604] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  160.866847] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  160.874092] PKRU: 55555554
[  160.876847] Call Trace:
[  160.879338]  <TASK>
[  160.881477]  ? __die+0x20/0x60
[  160.884586]  ? page_fault_oops+0x15a/0x450
[  160.888746]  ? search_extable+0x22/0x30
[  160.892647]  ? search_bpf_extables+0x5f/0x80
[  160.896988]  ? exc_page_fault+0xa9/0x140
[  160.900973]  ? asm_exc_page_fault+0x22/0x30
[  160.905232]  ? dev_map_free+0x77/0x170
[  160.909043]  ? dev_map_free+0x58/0x170
[  160.912857]  bpf_map_free_deferred+0x51/0x90
[  160.917196]  process_one_work+0x142/0x370
[  160.921272]  worker_thread+0x29e/0x3b0
[  160.925082]  ? rescuer_thread+0x4b0/0x4b0
[  160.929157]  kthread+0xd4/0x110
[  160.932355]  ? kthread_park+0x80/0x80
[  160.936079]  ret_from_fork+0x2d/0x50
[  160.943396]  ? kthread_park+0x80/0x80
[  160.950803]  ret_from_fork_asm+0x11/0x20
[  160.958482]  </TASK>

Fixes: 546ac1ffb70d ("bpf: add devmap, a map for storing net device references")
CC: stable@vger.kernel.org
Reported-by: Jordy Zomer <jordyzomer@google.com>
Suggested-by: Jordy Zomer <jordyzomer@google.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
---
 kernel/bpf/devmap.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index 7878be18e9d2..3aa002a47a96 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -184,7 +184,7 @@ static struct bpf_map *dev_map_alloc(union bpf_attr *attr)
 static void dev_map_free(struct bpf_map *map)
 {
 	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
-	int i;
+	u32 i;
 
 	/* At this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,
 	 * so the programs (can be more than one that used this map) were
@@ -821,7 +821,7 @@ static long dev_map_delete_elem(struct bpf_map *map, void *key)
 {
 	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
 	struct bpf_dtab_netdev *old_dev;
-	int k = *(u32 *)key;
+	u32 k = *(u32 *)key;
 
 	if (k >= map->max_entries)
 		return -EINVAL;
@@ -838,7 +838,7 @@ static long dev_map_hash_delete_elem(struct bpf_map *map, void *key)
 {
 	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
 	struct bpf_dtab_netdev *old_dev;
-	int k = *(u32 *)key;
+	u32 k = *(u32 *)key;
 	unsigned long flags;
 	int ret = -ENOENT;
 
-- 
2.34.1

Re: [PATCH v2 bpf 0/2] bpf: fix OOB accesses in map_delete_elem callbacks

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Fri, 22 Nov 2024 13:10:28 +0100 you wrote:
> v1->v2:
> - CC stable and collect tags from Toke & John
> 
> Hi,
> 
> Jordy reported that for big enough XSKMAPs and DEVMAPs, when deleting
> elements, OOB writes occur.
> 
> [...]

Here is the summary with links:
  - [v2,bpf,1/2] xsk: fix OOB map writes when deleting elements
    https://git.kernel.org/bpf/bpf/c/32cd3db7de97
  - [v2,bpf,2/2] bpf: fix OOB devmap writes when deleting elements
    https://git.kernel.org/bpf/bpf/c/ab244dd7cf4c

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

Re: [PATCH v2 bpf 0/2] bpf: fix OOB accesses in map_delete_elem callbacks

[Cong Wang]

On Fri, Nov 22, 2024 at 01:10:28PM +0100, Maciej Fijalkowski wrote:
> v1->v2:
> - CC stable and collect tags from Toke & John
> 
> Hi,
> 
> Jordy reported that for big enough XSKMAPs and DEVMAPs, when deleting
> elements, OOB writes occur.
> 
> Reproducer below:
> 

Please consider adding it to tools/testing/selftests/bpf/, since it is
pretty small and self-contained. (A follow up patch is definitely
welcome.)

Thanks.