Commit 31b4beb4 authored Sep 19, 2016 by Kirill A. Shutemov Committed by Linus Torvalds Sep 19, 2016

ipc/shm: fix crash if CONFIG_SHMEM is not set

Commit c01d5b30 ("shmem: get_unmapped_area align huge page") makes
use of shm_get_unmapped_area() in shm_file_operations() unconditional to
CONFIG_MMU.

As Tony Battersby pointed this can lead NULL-pointer dereference on
machine with CONFIG_MMU=y and CONFIG_SHMEM=n.  In this case ipc/shm is
backed by ramfs which doesn't provide f_op->get_unmapped_area for
configurations with MMU.

The solution is to provide dummy f_op->get_unmapped_area for ramfs when
CONFIG_MMU=y, which just call current->mm->get_unmapped_area().

Fixes: c01d5b30 ("shmem: get_unmapped_area align huge page")
Link: http://lkml.kernel.org/r/20160912102704.140442-1-kirill.shutemov@linux.intel.com


Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: Tony Battersby <tonyb@cybernetics.com>
Tested-by: Tony Battersby <tonyb@cybernetics.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>	[4.7.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent c8de641b

fs/ramfs/file-mmu.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -27,9 +27,17 @@
		#include <linux/fs.h>
		#include <linux/mm.h>
		#include <linux/ramfs.h>
		#include <linux/sched.h>

		#include "internal.h"

		static unsigned long ramfs_mmu_get_unmapped_area(struct file *file,
		unsigned long addr, unsigned long len, unsigned long pgoff,
		unsigned long flags)
		{
		return current->mm->get_unmapped_area(file, addr, len, pgoff, flags);
		}

		const struct file_operations ramfs_file_operations = {
		.read_iter = generic_file_read_iter,
		.write_iter = generic_file_write_iter,
		@@ -38,6 +46,7 @@ const struct file_operations ramfs_file_operations = {
		.splice_read = generic_file_splice_read,
		.splice_write = iter_file_splice_write,
		.llseek = generic_file_llseek,
		.get_unmapped_area = ramfs_mmu_get_unmapped_area,
		};

		const struct inode_operations ramfs_file_inode_operations = {

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