net: atm: fix crash due to unvalidated vcc pointer in sigd_send()

Summary

In the Linux kernel, the following vulnerability has been resolved: net: atm: fix crash due to unvalidated vcc pointer in sigd_send() Reproducer available at [1]. The ATM send path (sendmsg -> vcc_sendmsg -> sigd_send) reads the vcc pointer from msg->vcc and uses it directly without any validation. This pointer comes from userspace via sendmsg() and can be arbitrarily forged: int fd = socket(AF_ATMSVC, SOCK_DGRAM, 0); ioctl(fd, ATMSIGD_CTRL); // become ATM signaling daemon struct msghdr msg = { .msg_iov = &iov, ... }; (unsigned long )(buf + 4) = 0xdeadbeef; // fake vcc pointer sendmsg(fd, &msg, 0); // kernel dereferences 0xdeadbeef In normal operation, the kernel sends the vcc pointer to the signaling daemon via sigd_enq() when processing operations like connect(), bind(), or listen(). The daemon is expected to return the same pointer when responding. However, a malicious daemon can send arbitrary pointer values. Fix this by introducing find_get_vcc() which validates the pointer by searching through vcc_hash (similar to how sigd_close() iterates over all VCCs), and acquires a reference via sock_hold() if found. Since struct atm_vcc embeds struct sock as its first member, they share the same lifetime. Therefore using sock_hold/sock_put is sufficient to keep the vcc alive while it is being used. Note that there may be a race with sigd_close() which could mark the vcc with various flags (e.g., ATM_VF_RELEASED) after find_get_vcc() returns. However, sock_hold() guarantees the memory remains valid, so this race only affects the logical state, not memory safety. [1]: https://gist.github.com/mrpre/1ba5949c45529c511152e2f4c755b0f3

Timeline

1. Apr 8, 2026, 1:06 PM UTCCVE published
2. Oct 15, 2026, 1:15 AM UTCRecord last updated

Affected versions

• Linux Linux

  From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 · fixed in c96549d07dfdd51aadf0722cfb40711574424840; From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 · fixed in 1c8bda3df028d5e54134077dcd09f46ca8cfceb5; From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 · fixed in 3e1a8b00095246a9a2b46b57f6d471c6d3c00ed2; From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 · fixed in e3f80666c2739296c3b69a127300455c43aa1067; From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 · fixed in 21c303fec138c002f90ed33bce60e807d53072bb; From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 · fixed in 69d3f9ee5489e6e8b66defcfa226e91d82393297; From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 · fixed in 440c9a5fc477a8ee259d8bf669531250b8398651; From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 · fixed in ae88a5d2f29b69819dc7b04086734439d074a643

• Linux Linux

  2.6.12

• KernelLinux

  From 2.6.12 · fixed in 5.10.252; From 5.11.0 · fixed in 5.15.202; From 5.16.0 · fixed in 6.1.165; From 6.2.0 · fixed in 6.6.128; From 6.7.0 · fixed in 6.12.75; From 6.13.0 · fixed in 6.18.14; From 6.19.0 · fixed in 6.19.4

References 8