mm: enforce __must_check on VMA merge and split

It is of critical importance to check the return results on VMA merge (and
split), failure to do so can result in use-after-free's.  This bug has
recurred, so have the compiler enforce this check to prevent any future
repetition.

Link: https://lkml.kernel.org/r/20241206225036.273103-1-lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/vma.c b/mm/vma.c
index 06554a732bce14e02ddcd57d4616d099e08a4e3e..6fa240e5b0c51474852068a702512ea6cf75a020 100644 (file)
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -447,8 +447,9 @@ void unmap_region(struct ma_state *mas, struct vm_area_struct *vma,
  * has already been checked or doesn't make sense to fail.
  * VMA Iterator will point to the original VMA.
  */
-static int __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
-                      unsigned long addr, int new_below)
+static __must_check int
+__split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
+           unsigned long addr, int new_below)
 {
        struct vma_prepare vp;
        struct vm_area_struct *new;
@@ -710,7 +711,8 @@ static bool can_merge_remove_vma(struct vm_area_struct *vma)
  * - The caller must hold a WRITE lock on the mm_struct->mmap_lock.
  * - vmi must be positioned within [@vmg->vma->vm_start, @vmg->vma->vm_end).
  */
-static struct vm_area_struct *vma_merge_existing_range(struct vma_merge_struct *vmg)
+static __must_check struct vm_area_struct *vma_merge_existing_range(
+               struct vma_merge_struct *vmg)
 {
        struct vm_area_struct *vma = vmg->vma;
        struct vm_area_struct *prev = vmg->prev;

diff --git a/mm/vma.h b/mm/vma.h
index 295d44ea54db39962876dc254d381f36ce4a1e05..61ed044b61458c51614f02591a9d885d81924c81 100644 (file)
--- a/mm/vma.h
+++ b/mm/vma.h
@@ -139,9 +139,10 @@ void validate_mm(struct mm_struct *mm);
 #define validate_mm(mm) do { } while (0)
 #endif
 
-int vma_expand(struct vma_merge_struct *vmg);
-int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
-              unsigned long start, unsigned long end, pgoff_t pgoff);
+__must_check int vma_expand(struct vma_merge_struct *vmg);
+__must_check int vma_shrink(struct vma_iterator *vmi,
+               struct vm_area_struct *vma,
+               unsigned long start, unsigned long end, pgoff_t pgoff);
 
 static inline int vma_iter_store_gfp(struct vma_iterator *vmi,
                        struct vm_area_struct *vma, gfp_t gfp)
@@ -174,13 +175,14 @@ void unmap_region(struct ma_state *mas, struct vm_area_struct *vma,
                struct vm_area_struct *prev, struct vm_area_struct *next);
 
 /* We are about to modify the VMA's flags. */
-struct vm_area_struct *vma_modify_flags(struct vma_iterator *vmi,
+__must_check struct vm_area_struct
+*vma_modify_flags(struct vma_iterator *vmi,
                struct vm_area_struct *prev, struct vm_area_struct *vma,
                unsigned long start, unsigned long end,
                unsigned long new_flags);
 
 /* We are about to modify the VMA's flags and/or anon_name. */
-struct vm_area_struct
+__must_check struct vm_area_struct
 *vma_modify_flags_name(struct vma_iterator *vmi,
                       struct vm_area_struct *prev,
                       struct vm_area_struct *vma,
@@ -190,7 +192,7 @@ struct vm_area_struct
                       struct anon_vma_name *new_name);
 
 /* We are about to modify the VMA's memory policy. */
-struct vm_area_struct
+__must_check struct vm_area_struct
 *vma_modify_policy(struct vma_iterator *vmi,
                   struct vm_area_struct *prev,
                   struct vm_area_struct *vma,
@@ -198,7 +200,7 @@ struct vm_area_struct
                   struct mempolicy *new_pol);
 
 /* We are about to modify the VMA's flags and/or uffd context. */
-struct vm_area_struct
+__must_check struct vm_area_struct
 *vma_modify_flags_uffd(struct vma_iterator *vmi,
                       struct vm_area_struct *prev,
                       struct vm_area_struct *vma,
@@ -206,11 +208,13 @@ struct vm_area_struct
                       unsigned long new_flags,
                       struct vm_userfaultfd_ctx new_ctx);
 
-struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg);
+__must_check struct vm_area_struct
+*vma_merge_new_range(struct vma_merge_struct *vmg);
 
-struct vm_area_struct *vma_merge_extend(struct vma_iterator *vmi,
-                                       struct vm_area_struct *vma,
-                                       unsigned long delta);
+__must_check struct vm_area_struct
+*vma_merge_extend(struct vma_iterator *vmi,
+                 struct vm_area_struct *vma,
+                 unsigned long delta);
 
 void unlink_file_vma_batch_init(struct unlink_vma_file_batch *vb);