+ mmap-fix-vma_iterator-in-error-path-of-vma_merge.patch added to mm-hotfixes-unstable branch

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The patch titled
     Subject: mmap: fix vma_iterator in error path of vma_merge()
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mmap-fix-vma_iterator-in-error-path-of-vma_merge.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mmap-fix-vma_iterator-in-error-path-of-vma_merge.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>
Subject: mmap: fix vma_iterator in error path of vma_merge()
Date: Fri, 29 Sep 2023 14:30:39 -0400

During the error path, the vma iterator may not be correctly positioned or
set to the correct range.  Undo the vma_prev() call by resetting to the
passed in address.  Re-walking to the same range will fix the range to the
area previously passed in.

Users would notice increased cycles as vma_merge() would be called an
extra time with vma == prev, and thus would fail to merge and return.

Link: https://lore.kernel.org/linux-mm/CAG48ez12VN1JAOtTNMY+Y2YnsU45yL5giS-Qn=ejtiHpgJAbdQ@xxxxxxxxxxxxxx/
Link: https://lkml.kernel.org/r/20230929183041.2835469-2-Liam.Howlett@xxxxxxxxxx
Fixes: 18b098af2890 ("vma_merge: set vma iterator to correct position.")
Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Reported-by: Jann Horn <jannh@xxxxxxxxxx>
Closes: https://lore.kernel.org/linux-mm/CAG48ez12VN1JAOtTNMY+Y2YnsU45yL5giS-Qn=ejtiHpgJAbdQ@xxxxxxxxxxxxxx/
Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/mmap.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

--- a/mm/mmap.c~mmap-fix-vma_iterator-in-error-path-of-vma_merge
+++ a/mm/mmap.c
@@ -975,7 +975,7 @@ struct vm_area_struct *vma_merge(struct
 
 	/* Error in anon_vma clone. */
 	if (err)
-		return NULL;
+		goto anon_vma_fail;
 
 	if (vma_start < vma->vm_start || vma_end > vma->vm_end)
 		vma_expanded = true;
@@ -988,7 +988,7 @@ struct vm_area_struct *vma_merge(struct
 	}
 
 	if (vma_iter_prealloc(vmi, vma))
-		return NULL;
+		goto prealloc_fail;
 
 	init_multi_vma_prep(&vp, vma, adjust, remove, remove2);
 	VM_WARN_ON(vp.anon_vma && adjust && adjust->anon_vma &&
@@ -1016,6 +1016,12 @@ struct vm_area_struct *vma_merge(struct
 	vma_complete(&vp, vmi, mm);
 	khugepaged_enter_vma(res, vm_flags);
 	return res;
+
+prealloc_fail:
+anon_vma_fail:
+	vma_iter_set(vmi, addr);
+	vma_iter_load(vmi);
+	return NULL;
 }
 
 /*
_

Patches currently in -mm which might be from Liam.Howlett@xxxxxxxxxx are

maple_tree-add-mas_active-to-detect-in-tree-walks.patch
maple_tree-add-mas_underflow-and-mas_overflow-states.patch
mm-mempolicy-fix-set_mempolicy_home_node-previous-vma-pointer.patch
mmap-fix-vma_iterator-in-error-path-of-vma_merge.patch
mmap-fix-error-paths-with-dup_anon_vma.patch




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