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ipc/shm: fix crash if CONFIG_SHMEM is not set 

Commit c01d5b3007 ("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: c01d5b3007 ("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>
This commit is contained in:
Kirill A. Shutemov 2016-09-19 14:44:18 -07:00 committed by Linus Torvalds
parent c8de641b1e
commit 31b4beb473
1 changed files with 9 additions and 0 deletions
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9
fs/ramfs/file-mmu.c
View File

@ -27,9 +27,17 @@
#include <linux/fs.h> #include <linux/fs.h>
#include <linux/mm.h> #include <linux/mm.h>
#include <linux/ramfs.h> #include <linux/ramfs.h>
#include <linux/sched.h>
#include "internal.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 = { const struct file_operations ramfs_file_operations = {
.read_iter = generic_file_read_iter, .read_iter = generic_file_read_iter,
.write_iter = generic_file_write_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_read = generic_file_splice_read,
.splice_write = iter_file_splice_write, .splice_write = iter_file_splice_write,
.llseek = generic_file_llseek, .llseek = generic_file_llseek,
.get_unmapped_area = ramfs_mmu_get_unmapped_area,
}; };
const struct inode_operations ramfs_file_inode_operations = { const struct inode_operations ramfs_file_inode_operations = {