[PATCH] mm/vmalloc: fix the unchecked dereference warning in vread_iter()

[Baoquan He]

LKP reported smatch warning as below:

===================
smatch warnings:
mm/vmalloc.c:3689 vread_iter() error: we previously assumed 'vm' could be null (see line 3667)
......
06c8994626d1b7  @3667 size = vm ? get_vm_area_size(vm) : va_size(va);
......
06c8994626d1b7  @3689 else if (!(vm->flags & VM_IOREMAP))
                                 ^^^^^^^^^
Unchecked dereference
=====================

So add checking on whether 'vm' is not null when dereferencing it in
vread_iter(). This mutes smatch complaint.

Reported-by: kernel test robot <lkp@xxxxxxxxx>
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Closes: https://lore.kernel.org/r/202310171600.WCrsOwFj-lkp@xxxxxxxxx/
Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
---
 mm/vmalloc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index aad48ed8d86b..2cc992392db7 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -3813,7 +3813,7 @@ long vread_iter(struct iov_iter *iter, const char *addr, size_t count)
 
 		if (flags & VMAP_RAM)
 			copied = vmap_ram_vread_iter(iter, addr, n, flags);
-		else if (!(vm->flags & VM_IOREMAP))
+		else if (!(vm && (vm->flags & VM_IOREMAP)))
 			copied = aligned_vread_iter(iter, addr, n);
 		else /* IOREMAP area is treated as memory hole */
 			copied = zero_iter(iter, n);
-- 
2.41.0