On 04.10.2024 09:21, Peter Xu wrote:
On Fri, Oct 04, 2024 at 06:35:53PM +0530, Manas via B4 Relay wrote:
From: Manas <manas18244@xxxxxxxxxxx>
syzbot has pointed to a possible null pointer dereference in
pfnmap_lockdep_assert. vm_file member of vm_area_struct is being
dereferenced without any checks.
This fix returns if vm_file member in vm_area_struct is NULL.
Reported-by: syzbot+093d096417e7038a689b@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=093d096417e7038a689b
---
This bug[1] triggers a general protection fault in follow_pfnmap_start
function. An assertion pfnmap_lockdep_assert inside this function
dereferences vm_file member of vm_area_struct. And panic gets triggered
when vm_file is NULL.
This patch returns from the assertion pfnmap_lockdep_assert if vm_file
is found to be NULL.
[1] https://syzkaller.appspot.com/bug?extid=093d096417e7038a689b
Signed-off-by: Manas <manas18244@xxxxxxxxxxx>
Reviewed-by: Peter Xu <peterx@xxxxxxxxxx>
One nitpick:
---
Changes in v2:
- v2: use ternary operator according to feedback
- Link to v1: https://lore.kernel.org/r/20241003-fix-null-deref-v1-1-0a45df9d016a@xxxxxxxxxxx
---
mm/memory.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/memory.c b/mm/memory.c
index 2366578015ad..5ed109a8f02e 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -6346,7 +6346,7 @@ static inline void pfnmap_args_setup(struct follow_pfnmap_args *args,
static inline void pfnmap_lockdep_assert(struct vm_area_struct *vma)
{
#ifdef CONFIG_LOCKDEP
- struct address_space *mapping = vma->vm_file->f_mapping;
+ struct address_space *mapping = vma->vm_file ? vma->vm_file->f_mapping : NULL;
if (mapping)
lockdep_assert(lockdep_is_held(&vma->vm_file->f_mapping->i_mmap_rwsem) ||
This can use "mapping" directly, as I mentioned in previous email (but
probably got overlooked..).
Thanks!
Oh no! I missed it. Sending v3...
---
base-commit: 9852d85ec9d492ebef56dc5f229416c925758edc
change-id: 20241003-fix-null-deref-6bfa0337efc3
Best regards,
--
Manas <manas18244@xxxxxxxxxxx>
--
Peter Xu
--
Manas
