CVE-2025-38185

In the Linux kernel, the following vulnerability has been resolved:

atm: atmtcp: Free invalid length skb in atmtcpcsend().

syzbot reported the splat below. [0]

vcc_sendmsg() copies data passed from userspace to skb and passes it to vcc->dev->ops->send().

atmtcpcsend() accesses skb->data as struct atmtcp_hdr after checking if skb->len is 0, but it's not enough.

Also, when skb->len == 0, skb and sk (vcc) were leaked because devkfreeskb() is not called and skwmemalloc adjustment is missing to revert atmaccounttx() in vccsendmsg(), which is expected to be done in atmpop_raw().

Let's properly free skb with an invalid length in atmtcpcsend().

atmtcpcsend+0x255/0xed0 drivers/atm/atmtcp.c:294 vccsendmsg+0xd7c/0xff0 net/atm/common.c:644 socksendmsg_nosec net/socket.c:712 [inline] __sock_sendmsg+0x330/0x3d0 net/socket.c:727 ____sys_sendmsg+0x7e0/0xd80 net/socket.c:2566 ___sys_sendmsg+0x271/0x3b0 net/socket.c:2620 __sys_sendmsg net/socket.c:2652 [inline] __dosyssendmsg net/socket.c:2657 [inline] __sesyssendmsg net/socket.c:2655 [inline] _x64syssendmsg+0x211/0x3e0 net/socket.c:2655 x64syscall+0x32fb/0x3db0 arch/x86/include/generated/asm/syscalls64.h:47 dosyscallx64 arch/x86/entry/syscall64.c:63 [inline] dosyscall64+0xd9/0x210 arch/x86/entry/syscall64.c:94 entrySYSCALL64afterhwframe+0x77/0x7f

Uninit was created at: slabpostallochook mm/slub.c:4154 [inline] slaballocnode mm/slub.c:4197 [inline] kmemcacheallocnodenoprof+0x818/0xf00 mm/slub.c:4249 kmallocreserve+0x13c/0x4b0 net/core/skbuff.c:579 __allocskb+0x347/0x7d0 net/core/skbuff.c:670 allocskb include/linux/skbuff.h:1336 [inline] vcc_sendmsg+0xb40/0xff0 net/atm/common.c:628 socksendmsgnosec net/socket.c:712 [inline] __sock_sendmsg+0x330/0x3d0 net/socket.c:727 ____sys_sendmsg+0x7e0/0xd80 net/socket.c:2566 ___sys_sendmsg+0x271/0x3b0 net/socket.c:2620 __sys_sendmsg net/socket.c:2652 [inline] __dosyssendmsg net/socket.c:2657 [inline] __sesyssendmsg net/socket.c:2655 [inline] _x64syssendmsg+0x211/0x3e0 net/socket.c:2655 x64syscall+0x32fb/0x3db0 arch/x86/include/generated/asm/syscalls64.h:47 dosyscallx64 arch/x86/entry/syscall64.c:63 [inline] dosyscall64+0xd9/0x210 arch/x86/entry/syscall64.c:94 entrySYSCALL64afterhwframe+0x77/0x7f

CPU: 1 UID: 0 PID: 5798 Comm: syz-executor192 Not tainted 6.16.0-rc1-syzkaller-00010-g2c4a1f3fe03e #0 PREEMPT(undef) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025