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If merge_across_nodes was manually set to 0 (not the default value) by the admin or a tuned profile on NUMA systems triggering cross-NODE page migrations, a stable_node use after free could materialize. If the chain is collapsed stable_node would point to the old chain that was already freed. stable_node_dup would be the stable_node dup now converted to a regular stable_node and indexed in the rbtree in replacement of the freed stable_node chain (not anymore a dup). This special case where the chain is collapsed in the NUMA replacement path, is now detected by setting stable_node to NULL by the chain_prune callee if it decides to collapse the chain. This tells the NUMA replacement code that even if stable_node and stable_node_dup are different, this is not a chain if stable_node is NULL, as the stable_node_dup was converted to a regular stable_node and the chain was collapsed. It is generally safer for the callee to force the caller stable_node to NULL the moment it become stale so any other mistake like this would result in an instant Oops easier to debug than an use after free. Otherwise the replace logic would act like if stable_node was a valid chain, when in fact it was freed. Notably stable_node_chain_add_dup(page_node, stable_node) would run on a stable stable_node. Andrey Ryabinin found the source of the use after free in chain_prune(). Link: http://lkml.kernel.org/r/20170512193805.8807-2-aarcange@redhat.com Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Reported-by: Andrey Ryabinin <aryabinin@virtuozzo.com> Reported-by: Evgheni Dereveanchin <ederevea@redhat.com> Tested-by: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Petr Holasek <pholasek@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: Gavin Guo <gavin.guo@canonical.com> Cc: Jay Vosburgh <jay.vosburgh@canonical.com> Cc: Mel Gorman <mgorman@techsingularity.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.