6.12-stable review patch. If anyone has any objections, please let me know.
------------------
From: Kuniyuki Iwashima kuniyu@google.com
[ Upstream commit ec79003c5f9d2c7f9576fc69b8dbda80305cbe3a ]
syzbot reported the splat below. [0]
When atmtcp_v_open() or atmtcp_v_close() is called via connect() or close(), atmtcp_send_control() is called to send an in-kernel special message.
The message has ATMTCP_HDR_MAGIC in atmtcp_control.hdr.length. Also, a pointer of struct atm_vcc is set to atmtcp_control.vcc.
The notable thing is struct atmtcp_control is uAPI but has a space for an in-kernel pointer.
struct atmtcp_control { struct atmtcp_hdr hdr; /* must be first */ ... atm_kptr_t vcc; /* both directions */ ... } __ATM_API_ALIGN;
typedef struct { unsigned char _[8]; } __ATM_API_ALIGN atm_kptr_t;
The special message is processed in atmtcp_recv_control() called from atmtcp_c_send().
atmtcp_c_send() is vcc->dev->ops->send() and called from 2 paths:
1. .ndo_start_xmit() (vcc->send() == atm_send_aal0()) 2. vcc_sendmsg()
The problem is sendmsg() does not validate the message length and userspace can abuse atmtcp_recv_control() to overwrite any kptr by atmtcp_control.
Let's add a new ->pre_send() hook to validate messages from sendmsg().
[0]: Oops: general protection fault, probably for non-canonical address 0xdffffc00200000ab: 0000 [#1] SMP KASAN PTI KASAN: probably user-memory-access in range [0x0000000100000558-0x000000010000055f] CPU: 0 UID: 0 PID: 5865 Comm: syz-executor331 Not tainted 6.17.0-rc1-syzkaller-00215-gbab3ce404553 #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025 RIP: 0010:atmtcp_recv_control drivers/atm/atmtcp.c:93 [inline] RIP: 0010:atmtcp_c_send+0x1da/0x950 drivers/atm/atmtcp.c:297 Code: 4d 8d 75 1a 4c 89 f0 48 c1 e8 03 42 0f b6 04 20 84 c0 0f 85 15 06 00 00 41 0f b7 1e 4d 8d b7 60 05 00 00 4c 89 f0 48 c1 e8 03 <42> 0f b6 04 20 84 c0 0f 85 13 06 00 00 66 41 89 1e 4d 8d 75 1c 4c RSP: 0018:ffffc90003f5f810 EFLAGS: 00010203 RAX: 00000000200000ab RBX: 0000000000000000 RCX: 0000000000000000 RDX: ffff88802a510000 RSI: 00000000ffffffff RDI: ffff888030a6068c RBP: ffff88802699fb40 R08: ffff888030a606eb R09: 1ffff1100614c0dd R10: dffffc0000000000 R11: ffffffff8718fc40 R12: dffffc0000000000 R13: ffff888030a60680 R14: 000000010000055f R15: 00000000ffffffff FS: 00007f8d7e9236c0(0000) GS:ffff888125c1c000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000000000045ad50 CR3: 0000000075bde000 CR4: 00000000003526f0 Call Trace: <TASK> vcc_sendmsg+0xa10/0xc60 net/atm/common.c:645 sock_sendmsg_nosec net/socket.c:714 [inline] __sock_sendmsg+0x219/0x270 net/socket.c:729 ____sys_sendmsg+0x505/0x830 net/socket.c:2614 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668 __sys_sendmsg net/socket.c:2700 [inline] __do_sys_sendmsg net/socket.c:2705 [inline] __se_sys_sendmsg net/socket.c:2703 [inline] __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2703 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f8d7e96a4a9 Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 18 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f8d7e923198 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 00007f8d7e9f4308 RCX: 00007f8d7e96a4a9 RDX: 0000000000000000 RSI: 0000200000000240 RDI: 0000000000000005 RBP: 00007f8d7e9f4300 R08: 65732f636f72702f R09: 65732f636f72702f R10: 65732f636f72702f R11: 0000000000000246 R12: 00007f8d7e9c10ac R13: 00007f8d7e9231a0 R14: 0000200000000200 R15: 0000200000000250 </TASK> Modules linked in:
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: syzbot+1741b56d54536f4ec349@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/68a6767c.050a0220.3d78fd.0011.GAE@google.com/ Tested-by: syzbot+1741b56d54536f4ec349@syzkaller.appspotmail.com Signed-off-by: Kuniyuki Iwashima kuniyu@google.com Link: https://patch.msgid.link/20250821021901.2814721-1-kuniyu@google.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/atm/atmtcp.c | 17 ++++++++++++++--- include/linux/atmdev.h | 1 + net/atm/common.c | 15 ++++++++++++--- 3 files changed, 27 insertions(+), 6 deletions(-)
diff --git a/drivers/atm/atmtcp.c b/drivers/atm/atmtcp.c index eeae160c898d3..fa3c76a2b49d1 100644 --- a/drivers/atm/atmtcp.c +++ b/drivers/atm/atmtcp.c @@ -279,6 +279,19 @@ static struct atm_vcc *find_vcc(struct atm_dev *dev, short vpi, int vci) return NULL; }
+static int atmtcp_c_pre_send(struct atm_vcc *vcc, struct sk_buff *skb) +{ + struct atmtcp_hdr *hdr; + + if (skb->len < sizeof(struct atmtcp_hdr)) + return -EINVAL; + + hdr = (struct atmtcp_hdr *)skb->data; + if (hdr->length == ATMTCP_HDR_MAGIC) + return -EINVAL; + + return 0; +}
static int atmtcp_c_send(struct atm_vcc *vcc,struct sk_buff *skb) { @@ -288,9 +301,6 @@ static int atmtcp_c_send(struct atm_vcc *vcc,struct sk_buff *skb) struct sk_buff *new_skb; int result = 0;
- if (skb->len < sizeof(struct atmtcp_hdr)) - goto done; - dev = vcc->dev_data; hdr = (struct atmtcp_hdr *) skb->data; if (hdr->length == ATMTCP_HDR_MAGIC) { @@ -347,6 +357,7 @@ static const struct atmdev_ops atmtcp_v_dev_ops = {
static const struct atmdev_ops atmtcp_c_dev_ops = { .close = atmtcp_c_close, + .pre_send = atmtcp_c_pre_send, .send = atmtcp_c_send };
diff --git a/include/linux/atmdev.h b/include/linux/atmdev.h index 45f2f278b50a8..70807c679f1ab 100644 --- a/include/linux/atmdev.h +++ b/include/linux/atmdev.h @@ -185,6 +185,7 @@ struct atmdev_ops { /* only send is required */ int (*compat_ioctl)(struct atm_dev *dev,unsigned int cmd, void __user *arg); #endif + int (*pre_send)(struct atm_vcc *vcc, struct sk_buff *skb); int (*send)(struct atm_vcc *vcc,struct sk_buff *skb); int (*send_bh)(struct atm_vcc *vcc, struct sk_buff *skb); int (*send_oam)(struct atm_vcc *vcc,void *cell,int flags); diff --git a/net/atm/common.c b/net/atm/common.c index d7f7976ea13ac..881c7f259dbd4 100644 --- a/net/atm/common.c +++ b/net/atm/common.c @@ -635,18 +635,27 @@ int vcc_sendmsg(struct socket *sock, struct msghdr *m, size_t size)
skb->dev = NULL; /* for paths shared with net_device interfaces */ if (!copy_from_iter_full(skb_put(skb, size), size, &m->msg_iter)) { - atm_return_tx(vcc, skb); - kfree_skb(skb); error = -EFAULT; - goto out; + goto free_skb; } if (eff != size) memset(skb->data + size, 0, eff-size); + + if (vcc->dev->ops->pre_send) { + error = vcc->dev->ops->pre_send(vcc, skb); + if (error) + goto free_skb; + } + error = vcc->dev->ops->send(vcc, skb); error = error ? error : size; out: release_sock(sk); return error; +free_skb: + atm_return_tx(vcc, skb); + kfree_skb(skb); + goto out; }
__poll_t vcc_poll(struct file *file, struct socket *sock, poll_table *wait)