[PATCH v7 11/49] vfs: allocate page instead of names_cache buffer in mount_block_root

Jeff Layton
2012-10-02T00:17:21Z

First, it's incorrect to call putname() after __getname_gfp() since the
bare __getname_gfp() call skips the auditing code, while putname()
doesn't.

mount_block_root allocates a PATH_MAX buffer via __getname_gfp, and then
calls get_fs_names to fill the buffer. That function can call
get_filesystem_list which assumes that that buffer is a full page in
size. On arches where PAGE_SIZE != 4k, then this could potentially
overrun.

In practice, it's hard to imagine the list of filesystem names even
approaching 4k, but it's best to be safe. Just allocate a page for this
purpose instead.

With this, we can also remove the __getname_gfp() definition since there
are no more callers.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
include/linux/fs.h | 3 +--
init/do_mounts.c | 7 ++++---
2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index aa11047..69513a7 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2221,8 +2221,7 @@ extern void __init vfs_caches_init(unsigned long);

extern struct kmem_cache *names_cachep;

-#define __getname_gfp(gfp) kmem_cache_alloc(names_cachep, (gfp))
-#define __getname() __getname_gfp(GFP_KERNEL)
+#define __getname() kmem_cache_alloc(names_cachep, GFP_KERNEL)
#define __putname(name) kmem_cache_free(names_cachep, (void *)(name))
#ifndef CONFIG_AUDITSYSCALL
#define putname(name) __putname(name)
diff --git a/init/do_mounts.c b/init/do_mounts.c
index d3f0aee..f8a6642 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -353,8 +353,9 @@ static int __init do_mount_root(char *name, char *fs, int flags, void *data)

void __init mount_block_root(char *name, int flags)
{
- char *fs_names = __getname_gfp(GFP_KERNEL
- | __GFP_NOTRACK_FALSE_POSITIVE);
+ struct page *page = alloc_page(GFP_KERNEL |
+ __GFP_NOTRACK_FALSE_POSITIVE);
+ char *fs_names = page_address(page);
char *p;
#ifdef CONFIG_BLOCK
char b[BDEVNAME_SIZE];
@@ -406,7 +407,7 @@ retry:
#endif
panic("VFS: Unable to mount root fs on %s", b);
out:
- putname(fs_names);
+ put_page(page);
}

#ifdef CONFIG_ROOT_NFS
--
1.7.11.4