From 31b4beb473e3bdee1bf79db849502dcb24b5c202 Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Mon, 19 Sep 2016 14:44:18 -0700 Subject: [PATCH] ipc/shm: fix crash if CONFIG_SHMEM is not set Commit c01d5b300774 ("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: c01d5b300774 ("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 Reported-by: Tony Battersby Tested-by: Tony Battersby Cc: Hugh Dickins Cc: [4.7.x] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/ramfs/file-mmu.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/fs/ramfs/file-mmu.c b/fs/ramfs/file-mmu.c index 183a212694bf..12af0490322f 100644 --- a/fs/ramfs/file-mmu.c +++ b/fs/ramfs/file-mmu.c @@ -27,9 +27,17 @@ #include #include #include +#include #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 = { -- 2.30.2