[PATCH v3 0/3] Fixes for vma_merge() error path

[Liam R. Howlett]

Jann Horn reported a potential vma iterator issue in the failure path of
the vma_merge() code.  After examining the interface, it seemed the best
course of action is to simply add an undo path in the unlikely case of
an error.

On examining the vma iterator issue, another issue was discovered that
would increase the memory usage during failure scenarios, so this is
addressed in patch 2.

Since it is unclear in the code, another patch adds comments to the
vma_merge() function on why dup_anon_vma() is safe in 'case 6'.

Changes since v2:
 - Updated dup_anon_vma() comment to include new argument.
 - Change vma iterator undo to a reset and rewalk to ensure
   vma_iter_config() changes are dropped. - Thanks Vlastimil Babka
 - Update user visible changes in patch 1 again. - Thanks Vlastimil
   Babka
 - Only set the anon_dup vma when the duplication is successful. -
   Thanks Vlastimil Babka

v2: https://lore.kernel.org/linux-mm/20230927160746.1928098-1-Liam.Howlett@xxxxxxxxxx/
v1: https://lore.kernel.org/linux-mm/20230927160746.1928098-1-Liam.Howlett@xxxxxxxxxx/

Liam R. Howlett (3):
  mmap: Fix vma_iterator in error path of vma_merge()
  mmap: Fix error paths with dup_anon_vma()
  mmap: Add clarifying comment to vma_merge() code

 mm/mmap.c | 45 +++++++++++++++++++++++++++++++++++----------
 1 file changed, 35 insertions(+), 10 deletions(-)

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2.40.1