mm/mremap: fix regression in vrm->new_addr check

Commit 3215eaceca87 ("mm/mremap: refactor initial parameter sanity
checks") moved the sanity check for vrm->new_addr from mremap_to() to
check_mremap_params().

However, this caused a regression as vrm->new_addr is now checked even
when MREMAP_FIXED and MREMAP_DONTUNMAP flags are not specified.  In this
case, vrm->new_addr can be garbage and create unexpected failures.

Fix this by moving the new_addr check after the vrm_implies_new_addr()
guard.  This ensures that the new_addr is only checked when the user has
specified one explicitly.

Link: https://lkml.kernel.org/r/20250828142657.770502-1-cmllamas@google.com
Fixes: 3215eaceca87 ("mm/mremap: refactor initial parameter sanity checks")
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Carlos Llamas <cmllamas@google.com>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/mremap.c b/mm/mremap.c
index e618a706aff5a6ef44b9a721fbc16d935acc5b49..35de0a7b910e085c3a2565c40aaa61d9e4a392de 100644 (file)
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -1774,15 +1774,18 @@ static unsigned long check_mremap_params(struct vma_remap_struct *vrm)
        if (!vrm->new_len)
                return -EINVAL;
 
-       /* Is the new length or address silly? */
-       if (vrm->new_len > TASK_SIZE ||
-           vrm->new_addr > TASK_SIZE - vrm->new_len)
+       /* Is the new length silly? */
+       if (vrm->new_len > TASK_SIZE)
                return -EINVAL;
 
        /* Remainder of checks are for cases with specific new_addr. */
        if (!vrm_implies_new_addr(vrm))
                return 0;
 
+       /* Is the new address silly? */
+       if (vrm->new_addr > TASK_SIZE - vrm->new_len)
+               return -EINVAL;
+
        /* The new address must be page-aligned. */
        if (offset_in_page(vrm->new_addr))
                return -EINVAL;