In the Linux kernel, the following vulnerability has been resolved:
USB: core: Fix hang in usb_kill_urb by adding memory barriers
The syzbot fuzzer has identified a bug in which processes hang waiting
for usb_kill_urb() to return. It turns out the issue is not unlinking
the URB; that works just fine. Rather, the problem arises when the
wakeup notification that the URB has completed is not received.
The reason is memory-access ordering on SMP systems. In outline form,
usb_kill_urb() and __usb_hcd_giveback_urb() operating concurrently on
different CPUs perform the following actions:
CPU 0 CPU 1
usb_kill_urb(): __usb_hcd_giveback_urb():
… …
atomic_inc(&urb->reject); atomic_dec(&urb->use_count);
… …
wait_event(usb_kill_urb_queue,
atomic_read(&urb->use_count) == 0);
if (atomic_read(&urb->reject))
wake_up(&usb_kill_urb_queue);
Confining your attention to urb->reject and urb->use_count, you can
see that the overall pattern of accesses on CPU 0 is:
write urb->reject, then read urb->use_count;
whereas the overall pattern of accesses on CPU 1 is:
write urb->use_count, then read urb->reject.
This pattern is referred to in memory-model circles as SB (for “Store
Buffering”), and it is well known that without suitable enforcement of
the desired order of accesses – in the form of memory barriers – it
is entirely possible for one or both CPUs to execute their reads ahead
of their writes. The end result will be that sometimes CPU 0 sees the
old un-decremented value of urb->use_count while CPU 1 sees the old
un-incremented value of urb->reject. Consequently CPU 0 ends up on
the wait queue and never gets woken up, leading to the observed hang
in usb_kill_urb().
The same pattern of accesses occurs in usb_poison_urb() and the
failure pathway of usb_hcd_submit_urb().
The problem is fixed by adding suitable memory barriers. To provide
proper memory-access ordering in the SB pattern, a full barrier is
required on both CPUs. The atomic_inc() and atomic_dec() accesses
themselves don’t provide any memory ordering, but since they are
present, we can use the optimized smp_mb__after_atomic() memory
barrier in the various routines to obtain the desired effect.
This patch adds the necessary memory barriers.
Vendor | Product | Version | CPE |
---|---|---|---|
linux | linux_kernel | * | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* |
[
{
"product": "Linux",
"vendor": "Linux",
"defaultStatus": "unaffected",
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"programFiles": [
"drivers/usb/core/hcd.c",
"drivers/usb/core/urb.c"
],
"versions": [
{
"version": "1da177e4c3f4",
"lessThan": "5f138ef224df",
"status": "affected",
"versionType": "git"
},
{
"version": "1da177e4c3f4",
"lessThan": "b50f5ca60475",
"status": "affected",
"versionType": "git"
},
{
"version": "1da177e4c3f4",
"lessThan": "546ba238535d",
"status": "affected",
"versionType": "git"
},
{
"version": "1da177e4c3f4",
"lessThan": "5904dfd3ddaf",
"status": "affected",
"versionType": "git"
},
{
"version": "1da177e4c3f4",
"lessThan": "9c61fce322ac",
"status": "affected",
"versionType": "git"
},
{
"version": "1da177e4c3f4",
"lessThan": "e3b131e30e61",
"status": "affected",
"versionType": "git"
},
{
"version": "1da177e4c3f4",
"lessThan": "9340226388c6",
"status": "affected",
"versionType": "git"
},
{
"version": "1da177e4c3f4",
"lessThan": "c9a18f7c5b07",
"status": "affected",
"versionType": "git"
},
{
"version": "1da177e4c3f4",
"lessThan": "26fbe9772b8c",
"status": "affected",
"versionType": "git"
}
]
},
{
"product": "Linux",
"vendor": "Linux",
"defaultStatus": "affected",
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"programFiles": [
"drivers/usb/core/hcd.c",
"drivers/usb/core/urb.c"
],
"versions": [
{
"version": "4.4.302",
"lessThanOrEqual": "4.4.*",
"status": "unaffected",
"versionType": "custom"
},
{
"version": "4.9.300",
"lessThanOrEqual": "4.9.*",
"status": "unaffected",
"versionType": "custom"
},
{
"version": "4.14.265",
"lessThanOrEqual": "4.14.*",
"status": "unaffected",
"versionType": "custom"
},
{
"version": "4.19.228",
"lessThanOrEqual": "4.19.*",
"status": "unaffected",
"versionType": "custom"
},
{
"version": "5.4.176",
"lessThanOrEqual": "5.4.*",
"status": "unaffected",
"versionType": "custom"
},
{
"version": "5.10.96",
"lessThanOrEqual": "5.10.*",
"status": "unaffected",
"versionType": "custom"
},
{
"version": "5.15.19",
"lessThanOrEqual": "5.15.*",
"status": "unaffected",
"versionType": "custom"
},
{
"version": "5.16.5",
"lessThanOrEqual": "5.16.*",
"status": "unaffected",
"versionType": "custom"
},
{
"version": "5.17",
"lessThanOrEqual": "*",
"status": "unaffected",
"versionType": "original_commit_for_fix"
}
]
}
]
git.kernel.org/stable/c/26fbe9772b8c459687930511444ce443011f86bf
git.kernel.org/stable/c/546ba238535d925254e0b3f12012a5c55801e2f3
git.kernel.org/stable/c/5904dfd3ddaff3bf4a41c3baf0a8e8f31ed4599b
git.kernel.org/stable/c/5f138ef224dffd15d5e5c5b095859719e0038427
git.kernel.org/stable/c/9340226388c66a7e090ebb00e91ed64a753b6c26
git.kernel.org/stable/c/9c61fce322ac2ef7fecf025285353570d60e41d6
git.kernel.org/stable/c/b50f5ca60475710bbc9a3af32fbfc17b1e69c2f0
git.kernel.org/stable/c/c9a18f7c5b071dce5e6939568829d40994866ab0
git.kernel.org/stable/c/e3b131e30e612ff0e32de6c1cb4f69f89db29193