In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
kcov: fix data corruption and race conditions on PREEMPT_RT<\/p>\n
syzbot is reporting KCOV state corruption on PREEMPT_RT kernels, for the
\ntemporary storage used for saving\/restoring remote KCOV state is currently
\nallocated as the per-CPU area.<\/p>\n
On PREEMPT_RT kernels, softirq handlers run as preemptible task threads
\n(e.g., ksoftirqd). If a softirq context preempts a task running a remote
\nKCOV session, it safely saves the task’s state into the per-CPU area.
\nHowever, if that softirq thread is subsequently preempted by a higher-
\npriority softirq thread on the same CPU, the second softirq will overwrite
\nthe same per-CPU area, permanently destroying the original task’s KCOV
\nstate.<\/p>\n
Fix this data corruption by moving the temporary storage from the per-CPU
\narea to the per-thread area. Since each softirq thread now owns its own
\ntask context, nested softirq preemption no longer causes data overwrites.<\/p>\n
Note that while the temporary storage is now on a per-thread basis, the
\nper-CPU kcov_percpu_data.lock must be retained, for we need to ensure that
\nkcov_remote_start() and kcov_remote_stop() operate atomically without
\nracing against asynchronous interrupts that manipulate the current task’s
\nKCOV state.<\/p>\n
It is likely that GFP_KERNEL allocation by vmalloc_node() in kcov_init()
\nhas already called panic() before returning NULL, for there will be no
\nOOM-killable userspace processes when __init function of built-in module
\nruns. But this patch also fixes crashing the kernel when vmalloc_node()
\nin kcov_init() returned NULL, for kcov_init() left per-CPU irq_area == NULL
\nbut kcov_remote_start() depends on per-CPU irq_area != NULL, resulting in<\/p>\n
(1) doing vmalloc() in kcov_remote_start() despite !in_task() context<\/p>\n
(2) out-of-array-bounds access if (1) succeeded but
\n kcov->remote_size < CONFIG_KCOV_IRQ_AREA_SIZE<\/p>\n
(3) always leak memory allocated by (1), eventually killing all
\n OOM-killable userspace processes<\/p>\n
problems.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
kcov: fix data corruption and race conditions on PREEMPT_RT<\/p>\n
syzbot is reporting KCOV state corruption on PREEMPT_RT kernels, for t<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-20399","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/20399","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln"}],"about":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/types\/vuln"}],"wp:attachment":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=20399"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=20399"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=20399"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}