RHSA-2015:2636: Important: kernel security and bug fix update

First published: Tue Dec 15 2015(Updated: )

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

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