RHEL 6: RHSA-2015:2636-01 Important Kernel Update with Security Risks

The kernel packages contain the Linux kernel, the core of any Linux operating system.
* A flaw was found in the way the Linux kernel's file system implementation handled rename operations in which the source was inside and the destination was outside of a bind mount. A privileged user inside a container could use this flaw to escape the bind mount and, potentially, escalate their privileges on the system. (CVE-2015-2925, Important)
* It was found that the x86 ISA (Instruction Set Architecture) is prone to a denial of service attack inside a virtualized environment in the form of an infinite loop in the microcode due to the way (sequential) delivering of benign exceptions such as #AC (alignment check exception) and #DB (debug exception) is handled. A privileged user inside a guest could use these flaws to create denial of service conditions on the host kernel. (CVE-2015-5307, CVE-2015-8104, Important)
* A race condition flaw was found in the way the Linux kernel's IPC subsystem initialized certain fields in an IPC object structure that were later used for permission checking before inserting the object into a globally visible list. A local, unprivileged user could potentially use this flaw to elevate their privileges on the system. (CVE-2015-7613, Important)
* It was found that the Linux kernel's keys subsystem did not correctly garbage collect uninstantiated keyrings. A local attacker could use this flaw to crash the system or, potentially, escalate their privileges on the system. (CVE-2015-7872, Important)
Red Hat would like to thank Ben Serebrin of Google Inc. for reporting the CVE-2015-5307 issue.
This update also fixes the following bugs:
* Previously, Human Interface Device (HID) ran a report on an unaligned buffer, which could cause a page fault interrupt and an oops when the end of the report was read. This update fixes this bug by padding the end of the report with extra bytes, so the reading of the report never crosses a page boundary. As a result, a page fault and subsequent oops no longer occur. (BZ#1268203)
* The NFS client was previously failing to detect a directory loop for some NFS server directory structures. This failure could cause NFS inodes to remain referenced after attempting to unmount the file system, leading to a kernel crash. Loop checks have been added to VFS, which effectively prevents this problem from occurring. (BZ#1272858)
* Due to a race whereby the nfs_wb_pages_cancel() and nfs_commit_release_pages() calls both removed a request from the nfs_inode struct type, the kernel panicked with negative nfs_inode.npages count. The provided upstream patch performs the required serialization by holding the inode i_lock over the check of PagePrivate and locking the request, thus preventing the race and kernel panic from occurring. (BZ#1273721)
* Due to incorrect URB_ISO_ASAP semantics, playing an audio file using a USB sound card could previously fail for some hardware configurations. This update fixes the bug, and playing audio from a USB sound card now works as expected. (BZ#1273916)
* Inside hugetlb, region data structures were protected by a combination of a memory map semaphore and a single hugetlb instance mutex. However, a page-fault scalability improvement backported to the kernel on previous releases removed the single hugetlb instance mutex and introduced a new mutex table, making the locking combination insufficient, leading to possible race windows that could cause corruption and undefined behavior. This update fixes the problem by introducing a required spinlock to the region tracking functions for proper serialization. The problem only affects software using huge pages through hugetlb interface. (BZ#1274599)
All kernel users are advised to upgrade to these updated packages, which contain backported patches to correct these issues. The system must be rebooted for this update to take effect.