Synopsis: Important: kernel security and bug fix update
Advisory ID: SLSA-2015:1623-1
Issue Date: 2015-08-13
CVE Numbers: CVE-2015-5366
Two flaws were found in the way the Linux kernel’s networking
implementation handled UDP packets with incorrect checksum values. A
remote attacker could potentially use these flaws to trigger an infinite
loop in the kernel, resulting in a denial of service on the system, or
cause a denial of service in applications using the edge triggered epoll
functionality. (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
previously not killed. In addition, once the negative child dentry was
killed, an unlinked and unused dentry was present in the cache. As a
consequence, deadlock could be caused by forcing the dentry eviction while
the file system in question was frozen. With this update, all unused
dentries are unhashed and evicted just after a successful directory
removal, which avoids the deadlock, and the system no longer hangs in the
* Due to the broken s_umount lock ordering, a race condition occurred when
an unlinked file was closed and the sync (or syncfs) utility was run at
the same time. As a consequence, deadlock occurred on a frozen file system
between sync and a process trying to unfreeze the file system. With this
update, sync (or syncfs) is skipped on a frozen file system, and deadlock
no longer occurs in the aforementioned situation.
* Previously, in the scenario when a file was opened by file handle
(fhandle) with its dentry not present in dcache (“cold dcache”) and then
making use of the unlink() and close() functions, the inode was not freed
upon the close() system call. As a consequence, the iput() final was
delayed indefinitely. A patch has been provided to fix this bug, and the
inode is now freed as expected.
* 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 provides
debuging information for kernel crashes as intended.
* Previously, running the multipath request queue caused regressions in
cases where paths failed regularly under I/O load. This regression
manifested as I/O stalls that exceeded 300 seconds. This update reverts
the changes aimed to reduce running the multipath request queue resulting
in I/O stalls completing in a timely manner.
The system must be rebooted for this update to take effect.
– Scientific Linux Development Team