In the Linux kernel, the following vulnerability has been resolved: sched/fair: Fix shift-out-of-bounds in load_balance() Syzbot reported a handful of occurrences where an sd->nr_balance_failed can grow to much higher values than one would expect. A successful load_balance() resets it to 0; a failed one increments it. Once it gets to sd->cache_nice_tries + 3, this *should* trigger an active balance, which will either set it to sd->cache_nice_tries+1 or reset it to 0. However, in case the to-be-active-balanced task is not allowed to run on env->dst_cpu, then the increment is done without any further modification. This could then be repeated ad nauseam, and would explain the absurdly high values reported by syzbot (86, 149). VincentG noted there is value in letting sd->cache_nice_tries grow, so the shift itself should be fixed. That means preventing: """ If the value of the right operand is negative or is greater than or equal to the width of the promoted left operand, the behavior is undefined. """ Thus we need to cap the shift exponent to BITS_PER_TYPE(typeof(lefthand)) - 1. I had a look around for other similar cases via coccinelle: @expr@ position pos; expression E1; expression E2; @@ ( E1 >> E2@pos | E1 >> E2@pos ) @cst depends on expr@ position pos; expression expr.E1; constant cst; @@ ( E1 >> cst@pos | E1 << cst@pos ) @script:python depends on !cst@ pos << expr.pos; exp << expr.E2; @@ # Dirty hack to ignore constexpr if exp.upper() != exp: coccilib.report.print_report(pos[0], "Possible UB shift here") The only other match in kernel/sched is rq_clock_thermal() which employs sched_thermal_decay_shift, and that exponent is already capped to 10, so that one is fine.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - In the Linux kernel, the following vulnerability has been resolved: sched/fair: Fix shift-out-of-bounds in     load_balance() Syzbot reported a handful of occurrences where an sd->nr_balance_failed can grow to much     higher values than one would expect. A successful load_balance() resets it to 0; a failed one increments     it. Once it gets to sd->cache_nice_tries + 3, this *should* trigger an active balance, which will either     set it to sd->cache_nice_tries+1 or reset it to 0. However, in case the to-be-active-balanced task is not     allowed to run on env->dst_cpu, then the increment is done without any further modification. This could     then be repeated ad nauseam, and would explain the absurdly high values reported by syzbot (86, 149).
    VincentG noted there is value in letting sd->cache_nice_tries grow, so the shift itself should be fixed.
    That means preventing:  If the value of the right operand is negative or is greater than or equal to     the width of the promoted left operand, the behavior is undefined.  Thus we need to cap the shift     exponent to BITS_PER_TYPE(typeof(lefthand)) - 1. I had a look around for other similar cases via     coccinelle: @expr@ position pos; expression E1; expression E2; @@ ( E1 >> E2@pos | E1 >> E2@pos ) @cst     depends on expr@ position pos; expression expr.E1; constant cst; @@ ( E1 >> cst@pos | E1 << cst@pos )     @script:python depends on !cst@ pos << expr.pos; exp << expr.E2; @@ # Dirty hack to ignore constexpr if     exp.upper() != exp: coccilib.report.print_report(pos[0], Possible UB shift here) The only other match in     kernel/sched is rq_clock_thermal() which employs sched_thermal_decay_shift, and that exponent is already     capped to 10, so that one is fine. (CVE-2021-47044)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Severity
246102	Linux Distros Unpatched Vulnerability : CVE-2021-47044	Nessus	Misc.	high
160459	Amazon Linux 2 : kernel, --advisory ALAS2KERNEL-5.10-2022-002 (ALASKERNEL-5.10-2022-002)	Nessus	Amazon Linux Local Security Checks	high

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CVE-2021-47044

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