CVE-2025-39673
In the Linux kernel, the following vulnerability has been resolved:
ppp: fix race conditions in ppp_fill_forward_path
ppp_fill_forward_path() has two race conditions:
-
The ppp->channels list can change between list_empty() and list_first_entry(), as ppp_lock() is not held. If the only channel is deleted in ppp_disconnect_channel(), list_first_entry() may access an empty head or a freed entry, and trigger a panic.
-
pch->chan can be NULL. When ppp_unregister_channel() is called, pch->chan is set to NULL before pch is removed from ppp->channels.
Fix these by using a lockless RCU approach:
- Use list_first_or_null_rcu() to safely test and access the first list entry.
- Convert list modifications on ppp->channels to their RCU variants and add synchronize_net() after removal.
- Check for a NULL pch->chan before dereferencing it.
| Software | From | Fixed in |
|---|---|---|
| linux / linux_kernel | 5.13 | 5.15.190 |
| linux / linux_kernel | 5.16 | 6.1.149 |
| linux / linux_kernel | 6.2 | 6.6.103 |
| linux / linux_kernel | 6.7 | 6.12.44 |
| linux / linux_kernel | 6.13 | 6.16.4 |
| linux / linux_kernel | 6.17-rc1 | 6.17-rc1.x |
| linux / linux_kernel | 6.17-rc2 | 6.17-rc2.x |
| debian / debian_linux | 11.0 | 11.0.x |
- https://git.kernel.org/stable/c/0417adf367a0af11adf7ace849af4638cfb573f7
- https://git.kernel.org/stable/c/0f1630be6fcca3f0c63e4b242ad202e5cde28a40
- https://git.kernel.org/stable/c/94731cc551e29511d85aa8dec61a6c071b1f2430
- https://git.kernel.org/stable/c/9a1969fbffc1f1900d92d7594b1b7d8d72ef3dc7
- https://git.kernel.org/stable/c/ca18d751bcc9faf5b7e82e9fae1223d103928181
- https://git.kernel.org/stable/c/f97f6475fdcb3c28ff3c55cc4b7bde632119ec08
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
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