linux-kernel - [PATCH] mm/mmap: Allow vma_expand() to lock both anon and file locks

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Date:   Thu, 16 Jun 2022 18:33:06 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] mm/mmap: Allow vma_expand() to lock both anon and file locks

vma_expand() was only locking either file or anon based locks but could
unlock both.  This caused a locking error in trinity fuzzer.  Allow both
locks to be taken and released.

Fixes: a5985220056d (mm/mmap: use advanced maple tree API for mmap_region())
Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
---
 mm/mmap.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 5599c36283dd..315c3ca118cb 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -592,6 +592,11 @@ inline int vma_expand(struct ma_state *mas, struct vm_area_struct *vma,
 
 	vma_adjust_trans_huge(vma, start, end, 0);
 
+	if (anon_vma) {
+		anon_vma_lock_write(anon_vma);
+		anon_vma_interval_tree_pre_update_vma(vma);
+	}
+
 	if (file) {
 		mapping = file->f_mapping;
 		root = &mapping->i_mmap;
@@ -599,9 +604,6 @@ inline int vma_expand(struct ma_state *mas, struct vm_area_struct *vma,
 		i_mmap_lock_write(mapping);
 		flush_dcache_mmap_lock(mapping);
 		vma_interval_tree_remove(vma, root);
-	} else if (anon_vma) {
-		anon_vma_lock_write(anon_vma);
-		anon_vma_interval_tree_pre_update_vma(vma);
 	}
 
 	vma->vm_start = start;
@@ -620,15 +622,16 @@ inline int vma_expand(struct ma_state *mas, struct vm_area_struct *vma,
 		__remove_shared_vm_struct(next, file, mapping);
 	}
 
+	if (file) {
+		i_mmap_unlock_write(mapping);
+		uprobe_mmap(vma);
+	}
+
 	if (anon_vma) {
 		anon_vma_interval_tree_post_update_vma(vma);
 		anon_vma_unlock_write(anon_vma);
 	}
 
-	if (file) {
-		i_mmap_unlock_write(mapping);
-		uprobe_mmap(vma);
-	}
 
 	if (remove_next) {
 		if (file) {
-- 
2.35.1