CVE-2021-47069 (GCVE-0-2021-47069)
Vulnerability from cvelistv5
Published
2024-03-01 21:15
Modified
2026-05-11 13:47
Severity ?
Summary
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.
References
Impacted products
Vendor Product Version
Linux Linux Version: c5b2cbdbdac563f46ecd5e187253ab1abbd6fc04
Version: c5b2cbdbdac563f46ecd5e187253ab1abbd6fc04
Version: c5b2cbdbdac563f46ecd5e187253ab1abbd6fc04
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nipc/mqueue, msg, sem: avoid relying on a stack reference past its expiry\n\ndo_mq_timedreceive calls wq_sleep with a stack local address.  The\nsender (do_mq_timedsend) uses this address to later call pipelined_send.\n\nThis leads to a very hard to trigger race where a do_mq_timedreceive\ncall might return and leave do_mq_timedsend to rely on an invalid\naddress, causing the following crash:\n\n  RIP: 0010:wake_q_add_safe+0x13/0x60\n  Call Trace:\n   __x64_sys_mq_timedsend+0x2a9/0x490\n   do_syscall_64+0x80/0x680\n   entry_SYSCALL_64_after_hwframe+0x44/0xa9\n  RIP: 0033:0x7f5928e40343\n\nThe race occurs as:\n\n1. do_mq_timedreceive calls wq_sleep with the address of `struct\n   ext_wait_queue` on function stack (aliased as `ewq_addr` here) - it\n   holds a valid `struct ext_wait_queue *` as long as the stack has not\n   been overwritten.\n\n2. `ewq_addr` gets added to info-\u003ee_wait_q[RECV].list in wq_add, and\n   do_mq_timedsend receives it via wq_get_first_waiter(info, RECV) to call\n   __pipelined_op.\n\n3. Sender calls __pipelined_op::smp_store_release(\u0026this-\u003estate,\n   STATE_READY).  Here is where the race window begins.  (`this` is\n   `ewq_addr`.)\n\n4. If the receiver wakes up now in do_mq_timedreceive::wq_sleep, it\n   will see `state == STATE_READY` and break.\n\n5. do_mq_timedreceive returns, and `ewq_addr` is no longer guaranteed\n   to be a `struct ext_wait_queue *` since it was on do_mq_timedreceive\u0027s\n   stack.  (Although the address may not get overwritten until another\n   function happens to touch it, which means it can persist around for an\n   indefinite time.)\n\n6. do_mq_timedsend::__pipelined_op() still believes `ewq_addr` is a\n   `struct ext_wait_queue *`, and uses it to find a task_struct to pass to\n   the wake_q_add_safe call.  In the lucky case where nothing has\n   overwritten `ewq_addr` yet, `ewq_addr-\u003etask` is the right task_struct.\n   In the unlucky case, __pipelined_op::wake_q_add_safe gets handed a\n   bogus address as the receiver\u0027s task_struct causing the crash.\n\ndo_mq_timedsend::__pipelined_op() should not dereference `this` after\nsetting STATE_READY, as the receiver counterpart is now free to return.\nChange __pipelined_op to call wake_q_add_safe on the receiver\u0027s\ntask_struct returned by get_task_struct, instead of dereferencing `this`\nwhich sits on the receiver\u0027s stack.\n\nAs Manfred pointed out, the race potentially also exists in\nipc/msg.c::expunge_all and ipc/sem.c::wake_up_sem_queue_prepare.  Fix\nthose in the same way."
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