[PATCH 4.14 137/193] dax: fix general protection fault in dax_alloc_inode

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mikulas Patocka <mpatocka@xxxxxxxxxx>

commit 9f586fff6574f6ecbf323f92d44ffaf0d96225fe upstream.

Don't crash in case of allocation failure in dax_alloc_inode.

    syzkaller hit the following crash on e4880bc5dfb1

    kasan: CONFIG_KASAN_INLINE enabled
    kasan: GPF could be caused by NULL-ptr deref or user memory access
    [..]
    RIP: 0010:dax_alloc_inode+0x3b/0x70 drivers/dax/super.c:348
    Call Trace:
    alloc_inode+0x65/0x180 fs/inode.c:208
    new_inode_pseudo+0x69/0x190 fs/inode.c:890
    new_inode+0x1c/0x40 fs/inode.c:919
    mount_pseudo_xattr+0x288/0x560 fs/libfs.c:261
    mount_pseudo include/linux/fs.h:2137 [inline]
    dax_mount+0x2e/0x40 drivers/dax/super.c:388
    mount_fs+0x66/0x2d0 fs/super.c:1223

Fixes: 7b6be8444e0f ("dax: refactor dax-fs into a generic provider...")
Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/dax/super.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -344,6 +344,9 @@ static struct inode *dax_alloc_inode(str
 	struct inode *inode;
 
 	dax_dev = kmem_cache_alloc(dax_cache, GFP_KERNEL);
+	if (!dax_dev)
+		return NULL;
+
 	inode = &dax_dev->inode;
 	inode->i_rdev = 0;
 	return inode;