Vulnerability Details : CVE-2021-47069
In the Linux kernel, the following vulnerability has been resolved:
ipc/mqueue, msg, sem: avoid relying on a stack reference past its expiry
do_mq_timedreceive calls wq_sleep with a stack local address. The
sender (do_mq_timedsend) uses this address to later call pipelined_send.
This leads to a very hard to trigger race where a do_mq_timedreceive
call might return and leave do_mq_timedsend to rely on an invalid
address, causing the following crash:
RIP: 0010:wake_q_add_safe+0x13/0x60
Call Trace:
__x64_sys_mq_timedsend+0x2a9/0x490
do_syscall_64+0x80/0x680
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7f5928e40343
The race occurs as:
1. do_mq_timedreceive calls wq_sleep with the address of `struct
ext_wait_queue` on function stack (aliased as `ewq_addr` here) - it
holds a valid `struct ext_wait_queue *` as long as the stack has not
been overwritten.
2. `ewq_addr` gets added to info->e_wait_q[RECV].list in wq_add, and
do_mq_timedsend receives it via wq_get_first_waiter(info, RECV) to call
__pipelined_op.
3. Sender calls __pipelined_op::smp_store_release(&this->state,
STATE_READY). Here is where the race window begins. (`this` is
`ewq_addr`.)
4. If the receiver wakes up now in do_mq_timedreceive::wq_sleep, it
will see `state == STATE_READY` and break.
5. do_mq_timedreceive returns, and `ewq_addr` is no longer guaranteed
to be a `struct ext_wait_queue *` since it was on do_mq_timedreceive's
stack. (Although the address may not get overwritten until another
function happens to touch it, which means it can persist around for an
indefinite time.)
6. do_mq_timedsend::__pipelined_op() still believes `ewq_addr` is a
`struct ext_wait_queue *`, and uses it to find a task_struct to pass to
the wake_q_add_safe call. In the lucky case where nothing has
overwritten `ewq_addr` yet, `ewq_addr->task` is the right task_struct.
In the unlucky case, __pipelined_op::wake_q_add_safe gets handed a
bogus address as the receiver's task_struct causing the crash.
do_mq_timedsend::__pipelined_op() should not dereference `this` after
setting STATE_READY, as the receiver counterpart is now free to return.
Change __pipelined_op to call wake_q_add_safe on the receiver's
task_struct returned by get_task_struct, instead of dereferencing `this`
which sits on the receiver's stack.
As Manfred pointed out, the race potentially also exists in
ipc/msg.c::expunge_all and ipc/sem.c::wake_up_sem_queue_prepare. Fix
those in the same way.
Products affected by CVE-2021-47069
- cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
- cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
- cpe:2.3:o:linux:linux_kernel:5.13:rc1:*:*:*:*:*:*
- cpe:2.3:o:linux:linux_kernel:5.13:rc2:*:*:*:*:*:*
Exploit prediction scoring system (EPSS) score for CVE-2021-47069
0.04%
Probability of exploitation activity in the next 30 days
EPSS Score History
~ 5 %
Percentile, the proportion of vulnerabilities that are scored at or less
CVSS scores for CVE-2021-47069
Base Score | Base Severity | CVSS Vector | Exploitability Score | Impact Score | Score Source | First Seen |
---|---|---|---|---|---|---|
7.0
|
HIGH | CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H |
1.0
|
5.9
|
NIST | 2025-01-09 |
CWE ids for CVE-2021-47069
-
The product uses, accesses, or otherwise operates on a resource after that resource has been expired, released, or revoked.Assigned by: nvd@nist.gov (Primary)
References for CVE-2021-47069
-
https://git.kernel.org/stable/c/807fa14536b26803b858da878b643be72952a097
ipc/mqueue, msg, sem: avoid relying on a stack reference past its expiry - kernel/git/stable/linux.git - Linux kernel stable treePatch
-
https://git.kernel.org/stable/c/a11ddb37bf367e6b5239b95ca759e5389bb46048
ipc/mqueue, msg, sem: avoid relying on a stack reference past its expiry - kernel/git/stable/linux.git - Linux kernel stable treePatch
-
https://git.kernel.org/stable/c/4528c0c323085e645b8765913b4a7fd42cf49b65
ipc/mqueue, msg, sem: avoid relying on a stack reference past its expiry - kernel/git/stable/linux.git - Linux kernel stable treePatch
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