Overview
About vulnerability
In the Linux kernel, the following vulnerability has been resolved:
rseq: Fix segfault on registration when rseq_cs is non-zero
The rseq_cs field is documented as being set to 0 by user-space prior to registration, however this is not currently enforced by the kernel. This can result in a segfault on return to user-space if the value stored in the rseq_cs field doesn’t point to a valid struct rseq_cs.
The correct solution to this would be to fail the rseq registration when the rseq_cs field is non-zero. However, some older versions of glibc will reuse the rseq area of previous threads without clearing the rseq_cs field and will also terminate the process if the rseq registration fails in a secondary thread. This wasn’t caught in testing because in this case the leftover rseq_cs does point to a valid struct rseq_cs.
What we can do is clear the rseq_cs field on registration when it’s non-zero which will prevent segfaults on registration and won’t break the glibc versions that reuse rseq areas on thread creation.
Details
- Affected product:
- AlmaLinux 9.2 ESU , CentOS 8.4 ELS , CentOS 8.5 ELS , CentOS Stream 8 ELS , Oracle Linux 7 ELS , TuxCare 9.6 ESU , Ubuntu 20.04 ELS
- Affected packages:
- kernel @ 4.18.0 (+6 more)
In the Linux kernel, the following vulnerability has been resolved:
rseq: Fix segfault on registration when rseq_cs is non-zero
The rseq_cs field is documented as being set to 0 by user-space prior to registration, however this is not currently enforced by the kernel. This can result in a segfault on return to user-space if the value stored in the rseq_cs field doesn’t point to a valid struct rseq_cs.
The correct solution to this would be to fail the rseq registration when the rseq_cs field is non-zero. However, some older versions of glibc will reuse the rseq area of previous threads without clearing the rseq_cs field and will also terminate the process if the rseq registration fails in a secondary thread. This wasn’t caught in testing because in this case the leftover rseq_cs does point to a valid struct rseq_cs.
What we can do is clear the rseq_cs field on registration when it’s non-zero which will prevent segfaults on registration and won’t break the glibc versions that reuse rseq areas on thread creation.