+ maple_tree-fix-ma_state_prealloc-flag-in-mas_preallocate.patch added to mm-hotfixes-unstable branch

+ maple_tree-fix-ma_state_prealloc-flag-in-mas_preallocate.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: maple_tree: fix MA_STATE_PREALLOC flag in mas_preallocate()
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     maple_tree-fix-ma_state_prealloc-flag-in-mas_preallocate.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/maple_tree-fix-ma_state_prealloc-flag-in-mas_preallocate.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@oracle.com>
Subject: maple_tree: fix MA_STATE_PREALLOC flag in mas_preallocate()
Date: Mon, 16 Jun 2025 14:45:20 -0400

Temporarily clear the preallocation flag when explicitly requesting
allocations.  Pre-existing allocations are already counted against the
request through mas_node_count_gfp(), but the allocations will not happen
if the MA_STATE_PREALLOC flag is set.  This flag is meant to avoid
re-allocating in bulk allocation mode, and to detect issues with
preallocation calculations.

The MA_STATE_PREALLOC flag should also always be set on zero allocations
so that detection of underflow allocations will print a WARN_ON() during
consumption.

User visible effect of this flaw is a WARN_ON() followed by a null pointer
dereference when subsequent requests for larger number of nodes is
ignored, such as the vma merge retry in mmap_region() caused by drivers
altering the vma flags (which happens in v6.6, at least)

Link: https://lkml.kernel.org/r/20250616184521.3382795-3-Liam.Howlett@oracle.com
Fixes: 54a611b605901 ("Maple Tree: add new data structure")
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reported-by: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
Reported-by: Hailong Liu <hailong.liu@oppo.com>
Link: https://lore.kernel.org/all/1652f7eb-a51b-4fee-8058-c73af63bacd1@oppo.com/
Link: https://lore.kernel.org/all/20250428184058.1416274-1-Liam.Howlett@oracle.com/
Link: https://lore.kernel.org/all/20250429014754.1479118-1-Liam.Howlett@oracle.com/
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Hailong Liu <hailong.liu@oppo.com>
Cc: zhangpeng.00@bytedance.com <zhangpeng.00@bytedance.com>
Cc: Steve Kang <Steve.Kang@unisoc.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 lib/maple_tree.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/lib/maple_tree.c~maple_tree-fix-ma_state_prealloc-flag-in-mas_preallocate
+++ a/lib/maple_tree.c
@@ -5527,8 +5527,9 @@ int mas_preallocate(struct ma_state *mas
 	mas->store_type = mas_wr_store_type(&wr_mas);
 	request = mas_prealloc_calc(&wr_mas, entry);
 	if (!request)
-		return ret;
+		goto set_flag;
 
+	mas->mas_flags &= ~MA_STATE_PREALLOC;
 	mas_node_count_gfp(mas, request, gfp);
 	if (mas_is_err(mas)) {
 		mas_set_alloc_req(mas, 0);
@@ -5538,6 +5539,7 @@ int mas_preallocate(struct ma_state *mas
 		return ret;
 	}
 
+set_flag:
 	mas->mas_flags |= MA_STATE_PREALLOC;
 	return ret;
 }
_

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

maple_tree-fix-ma_state_prealloc-flag-in-mas_preallocate.patch
testing-raix-tree-maple-increase-readers-and-reduce-delay-for-faster-machines.patch