In the Linux kernel, the following vulnerability has been resolved:
zram: fix use-after-free in zram_writeback_endio
A crash was observed in zram_writeback_endio due to a NULL pointer
dereference in wake_up. The root cause is a race condition between the
bio completion handler (zram_writeback_endio) and the writeback task.
In zram_writeback_endio, wake_up() is called on &wb_ctl->done_wait after
releasing wb_ctl->done_lock. This creates a race window where the
writeback task can see num_inflight become 0, return, and free wb_ctl
before zram_writeback_endio calls wake_up().
CPU 0 (zram_writeback_endio) CPU 1 (writeback_store)
============================ ============================
zram_writeback_slots
zram_submit_wb_request
zram_submit_wb_request
wait_event(wb_ctl->done_wait)
spin_lock(&wb_ctl->done_lock);
list_add(&req->entry, &wb_ctl->done_reqs);
spin_unlock(&wb_ctl->done_lock);
wake_up(&wb_ctl->done_wait);
zram_complete_done_reqs
spin_lock(&wb_ctl->done_lock);
list_add(&req->entry, &wb_ctl->done_reqs);
spin_unlock(&wb_ctl->done_lock);
while (num_inflight) > 0)
spin_lock(&wb_ctl->done_lock);
list_del(&req->entry);
spin_unlock(&wb_ctl->done_lock);
// num_inflight becomes 0
atomic_dec(num_inflight);
// Leave zram_writeback_slots
// Free wb_ctl
release_wb_ctl(wb_ctl);
// UAF crash!
wake_up(&wb_ctl->done_wait);
This patch fixes this race by using RCU. By protecting wb_ctl with
rcu_read_lock() in zram_writeback_endio and using kfree_rcu() to free it,
we ensure that wb_ctl remains valid during the execution of
zram_writeback_endio.
References
Configurations
Configuration 1 (hide)
|
History
30 Oct 2026, 14:32
| Type | Values Removed | Values Added |
|---|---|---|
| CWE | CWE-416 | |
| First Time |
Linux linux Kernel
Linux |
|
| References | () https://git.kernel.org/stable/c/bf62f69574b19720ae5fbbbcdf24a0c4e3e05e43 - Patch | |
| References | () https://git.kernel.org/stable/c/ebe2cbefc86291fa7f386447a81995640df4e2fd - Patch | |
| CPE | cpe:2.3:o:linux:linux_kernel:7.1:rc4:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:7.1:rc1:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:7.1:rc2:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:7.1:rc5:*:*:*:*:*:* cpe:2.3:o:linux:linux_kernel:7.1:rc3:*:*:*:*:*:* |
Information
Published : 2026-07-19 16:17
Updated : 2026-10-30 14:32
NVD link : CVE-2026-63951
Mitre link : CVE-2026-63951
CVE.ORG link : CVE-2026-63951
JSON object : View
Products Affected
linux
- linux_kernel
CWE
CWE-416
Use After Free