RHSA-2015:1623: Important: kernel security and bug fix update

The kernel packages contain the Linux kernel, the core of any Linuxoperating system.Two flaws were found in the way the Linux kernel's networkingimplementation handled UDP packets with incorrect checksum values. A remoteattacker could potentially use these flaws to trigger an infinite loop inthe kernel, resulting in a denial of service on the system, or cause adenial of service in applications using the edge triggered epollfunctionality. (CVE-2015-5364, CVE-2015-5366, Important)This update also fixes the following bugs: When removing a directory, and a reference was held to that directory by a reference to a negative child dentry, the directory dentry was previouslynot killed. In addition, once the negative child dentry was killed, anunlinked and unused dentry was present in the cache. As a consequence,deadlock could be caused by forcing the dentry eviction while the filesystem in question was frozen. With this update, all unused dentries areunhashed and evicted just after a successful directory removal, whichavoids the deadlock, and the system no longer hangs in the aforementionedscenario. (BZ#1243400) Due to the broken sumount lock ordering, a race condition occurred when an unlinked file was closed and the sync (or syncfs) utility was run at thesame time. As a consequence, deadlock occurred on a frozen file systembetween sync and a process trying to unfreeze the file system. With thisupdate, sync (or syncfs) is skipped on a frozen file system, and deadlockno longer occurs in the aforementioned situation. (BZ#1243404) Previously, in the scenario when a file was opened by file handle (fhandle) with its dentry not present in dcache ("cold dcache") and thenmaking use of the unlink() and close() functions, the inode was not freedupon the close() system call. As a consequence, the iput() final wasdelayed indefinitely. A patch has been provided to fix this bug, and theinode is now freed as expected. (BZ#1243406) Due to a corrupted Executable and Linkable Format (ELF) header in the /proc/vmcore file, the kdump utility failed to provide any information.The underlying source code has been patched, and kdump now providesdebuging information for kernel crashes as intended. (BZ#1245195) Previously, running the multipath request queue caused regressions in cases where paths failed regularly under I/O load. This regressionmanifested as I/O stalls that exceeded 300 seconds. This update reverts thechanges aimed to reduce running the multipath request queue resulting inI/O completing in a timely manner. (BZ#1246095)All kernel users are advised to upgrade to these updated packages, whichcontain backported patches to correct these issues. The system must berebooted for this update to take effect.