mmap should return the start address of newly mapped area when successful. On a successful merge of a VMA, the return address was changed and thus was violating that expectation from userspace. This is a restoration of functionality provided by 309d08d9b3a3 (mm/mmap.c: fix mmap return value when vma is merged after call_mmap()). For completeness of fixing MAP_FIXED, implement the comments from the previous discussion to never update the address and fail if the address changes. Leaving the error as a WARN_ON() to avoid crashing the kernel. Cc: Liu Zixian <liuzixian4@xxxxxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: Jason Gunthorpe <jgg@xxxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Link: https://lore.kernel.org/all/Y06yk66SKxlrwwfb@lakrids/ Link: https://lore.kernel.org/all/20201203085350.22624-1-liuzixian4@xxxxxxxxxx/ Fixes: 4dd1b84140c1 (mm/mmap: use advanced maple tree API for mmap_region()) Reported-by: Mark Rutland <mark.rutland@xxxxxxx> Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> --- mm/mmap.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index 42cd2c260898..22010e13f1a1 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2625,14 +2625,14 @@ unsigned long mmap_region(struct file *file, unsigned long addr, if (error) goto unmap_and_free_vma; - /* Can addr have changed?? - * - * Answer: Yes, several device drivers can do it in their - * f_op->mmap method. -DaveM + /* + * Expansion is handled above, merging is handled below. + * Drivers should not alter the address of the VMA. */ - WARN_ON_ONCE(addr != vma->vm_start); - - addr = vma->vm_start; + if (WARN_ON((addr != vma->vm_start))) { + error = -EINVAL; + goto close_and_free_vma; + } mas_reset(&mas); /* @@ -2654,7 +2654,6 @@ unsigned long mmap_region(struct file *file, unsigned long addr, vm_area_free(vma); vma = merge; /* Update vm_flags to pick up the change. */ - addr = vma->vm_start; vm_flags = vma->vm_flags; goto unmap_writable; } -- 2.35.1
