In the Linux kernel, the following vulnerability has been resolved:
hdlc_ppp: sync per-proto timers before freeing hdlc state
Each PPP control protocol (LCP/IPCP/IPV6CP) embedded in struct ppp
registers a timer via timer_setup(). That struct ppp is the
hdlc->state allocation, which detach_hdlc_protocol() frees with kfree()
in both teardown paths: unregister_hdlc_device() and the re-attach inside
attach_hdlc_protocol().
The ppp proto never registered a .detach callback, so
detach_hdlc_protocol() performs no timer synchronization before the
kfree(). The only cancel, timer_delete(&proto->timer) in ppp_cp_event(),
is partial (it does not wait for a running callback) and only runs on the
->CLOSED transition; ppp_stop()/ppp_close() do not sync either. A
ppp_timer callback already executing (blocked on ppp->lock) survives the
kfree and then dereferences proto->state / ppp->lock in freed memory,
leading to a use-after-free.
Fix this by adding a .detach helper that calls timer_shutdown_sync() on
every per-proto timer. detach_hdlc_protocol() invokes proto->detach(dev)
before kfree(hdlc->state), so timer_shutdown_sync()
now runs on both free paths.
timer_shutdown_sync() is used instead of timer_delete_sync() because the
keepalive path re-arms the timer through add_timer()/mod_timer() and
shutdown blocks any re-activation during teardown.
Initialize the per-protocol timers in ppp_ioctl() when the protocol is
attached, and remove the now-redundant timer_setup() from ppp_start(), so
that the timers are initialized exactly once at attach time and
ppp_timer_release() never operates on uninitialized timer_list
structures. attach_hdlc_protocol() uses kmalloc() (not kzalloc), so
struct ppp's protos[i].timer is uninitialized garbage until the first
timer_setup(); without this init-at-attach, attaching the PPP protocol
without ever bringing the device up would leave timer_shutdown_sync()
operating on uninitialized memory in .detach. Moving the init out of
ppp_start() (which only runs on NETDEV_UP) into the attach path makes the
initialization unconditional and avoids initializing the same timer_list
twice.
This bug was found by static analysis.
References
Configurations
Configuration 1 (hide)
|
History
29 Jul 2026, 20:03
| Type | Values Removed | Values Added |
|---|---|---|
| CWE | CWE-416 | |
| References | () https://git.kernel.org/stable/c/508a0139d3bf60f6a03d2fbfb63a89a9463d983a - Patch | |
| References | () https://git.kernel.org/stable/c/5a84398101bf9f11e84b176343e4e3ba83e668c0 - Patch | |
| References | () https://git.kernel.org/stable/c/8308122bc9c065b1f376e081ed300129a2ac9545 - Patch | |
| References | () https://git.kernel.org/stable/c/86d80a231bde4cfb64bfbfbfffd83056fc93628f - Patch | |
| References | () https://git.kernel.org/stable/c/a594debfd4e7ec39413647458907f689ef57fd2f - Patch | |
| References | () https://git.kernel.org/stable/c/c64dbef1c0fbd36f9530aa75112acdf6a6d3cfd8 - Patch | |
| References | () https://git.kernel.org/stable/c/c78a4e41ab5ead6193ad8a2dd92e8906bae659fa - Patch | |
| References | () https://git.kernel.org/stable/c/ce8f9ddca0c9f217342a8b49efd309aa35b81a36 - Patch | |
| First Time |
Linux linux Kernel
Linux |
|
| CPE | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:2.6.12:-:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:2.6.12:rc4:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:2.6.12:rc5:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:2.6.12:rc2:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:2.6.12:rc3:*:*:*:*:*:* |
24 Jul 2026, 15:19
| Type | Values Removed | Values Added |
|---|---|---|
| References |
|
20 Jul 2026, 15:16
| Type | Values Removed | Values Added |
|---|---|---|
| CVSS |
v2 : v3 : |
v2 : unknown
v3 : 7.8 |
19 Jul 2026, 12:16
| Type | Values Removed | Values Added |
|---|---|---|
| New CVE |
Information
Published : 2026-07-19 12:16
Updated : 2026-07-29 20:03
NVD link : CVE-2026-63803
Mitre link : CVE-2026-63803
CVE.ORG link : CVE-2026-63803
JSON object : View
Products Affected
linux
- linux_kernel
CWE
CWE-416
Use After Free