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The cpu mask init code in "record__mmap_cpu_mask_init" function access "bits" array part of "struct mmap_cpu_mask". The size of this array is the value from cpu__max_cpu().cpu. This array is used to contain the cpumask value for each cpu. While setting bit for each cpu, it calls "set_bit" function which access index in "bits" array. If we provide a command line option to -C which is greater than the number of CPU's present in the system, the set_bit could access an array member which is out-of the array size. This is because currently, there is no boundary check for the CPU. This will result in seg fault: <<>> ./perf record -C 12341234 ls Perf can support 2048 CPUs. Consider raising MAX_NR_CPUS Segmentation fault (core dumped) <<>> Debugging with gdb, points to function flow as below: <<>> set_bit record__mmap_cpu_mask_init record__init_thread_default_masks record__init_thread_masks cmd_record <<>> Fix this by adding boundary check for the array. After the patch: <<>> ./perf record -C 12341234 ls Perf can support 2048 CPUs. Consider raising MAX_NR_CPUS Failed to initialize parallel data streaming masks <<>> With this fix, if -C is given a non-exsiting CPU, perf record will fail with: <<>> ./perf record -C 50 ls Failed to initialize parallel data streaming masks <<>> Reported-by: Nageswara R Sastry <rnsastry@linux.ibm.com> Signed-off-by: Athira Jajeev <atrajeev@linux.vnet.ibm.com> Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com> Tested-by: Nageswara R Sastry <rnsastry@linux.ibm.com> Cc: Jiri Olsa <jolsa@kernel.org> Cc: Kajol Jain <kjain@linux.ibm.com> Cc: Madhavan Srinivasan <maddy@linux.vnet.ibm.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: linuxppc-dev@lists.ozlabs.org Link: https://lore.kernel.org/r/20220905141929.7171-2-atrajeev@linux.vnet.ibm.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.