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mmap: fix do_brk_flags() modifying obviously incorrect VMAs 

Add more sanity checks to the VMA that do_brk_flags() will expand.  Ensure
the VMA matches basic merge requirements within the function before
calling can_vma_merge_after().

Drop the duplicate checks from vm_brk_flags() since they will be enforced
later.

The old code would expand file VMAs on brk(), which is functionally
wrong and also dangerous in terms of locking because the brk() path
isn't designed for file VMAs and therefore doesn't lock the file
mapping.  Checking can_vma_merge_after() ensures that new anonymous
VMAs can't be merged into file VMAs.

See https://lore.kernel.org/linux-mm/CAG48ez1tJZTOjS_FjRZhvtDA-STFmdw8PEizPDwMGFd_ui0Nrw@mail.gmail.com/

Link: https://lkml.kernel.org/r/20221205192304.1957418-1-Liam.Howlett@oracle.com
Fixes: 2e7ce7d354 ("mm/mmap: change do_brk_flags() to expand existing VMA and add do_brk_munmap()")
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Suggested-by: Jann Horn <jannh@google.com>
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: SeongJae Park <sj@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Liam Howlett 2022-12-05 19:23:17 +00:00 committed by Andrew Morton
parent 630dc25e43
commit 6c28ca6485
1 changed files with 3 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
mm/mmap.c
View File

@ -2948,9 +2948,9 @@ static int do_brk_flags(struct ma_state *mas, struct vm_area_struct *vma,
* Expand the existing vma if possible; Note that singular lists do not
* occur after forking, so the expand will only happen on new VMAs.
*/
if (vma &&
(!vma->anon_vma || list_is_singular(&vma->anon_vma_chain)) &&
((vma->vm_flags & ~VM_SOFTDIRTY) == flags)) {
if (vma && vma->vm_end == addr && !vma_policy(vma) &&
can_vma_merge_after(vma, flags, NULL, NULL,
addr >> PAGE_SHIFT, NULL_VM_UFFD_CTX, NULL)) {
mas_set_range(mas, vma->vm_start, addr + len - 1);
if (mas_preallocate(mas, vma, GFP_KERNEL))
return -ENOMEM;
@ -3037,11 +3037,6 @@ int vm_brk_flags(unsigned long addr, unsigned long request, unsigned long flags)
goto munmap_failed;
vma = mas_prev(&mas, 0);
if (!vma || vma->vm_end != addr || vma_policy(vma) ||
!can_vma_merge_after(vma, flags, NULL, NULL,
addr >> PAGE_SHIFT, NULL_VM_UFFD_CTX, NULL))
vma = NULL;
ret = do_brk_flags(&mas, vma, addr, len, flags);
populate = ((mm->def_flags & VM_LOCKED) != 0);
mmap_write_unlock(mm);