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maple_tree: fix MA_STATE_PREALLOC flag in mas_preallocate()

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commit fba46a5d83 upstream.

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: 54a611b605 ("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>
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Liam R. Howlett 2025-06-16 14:45:20 -04:00 committed by Greg Kroah-Hartman
parent 432c5363cd
commit e63032e66b
1 changed files with 8 additions and 5 deletions
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13
lib/maple_tree.c
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@ -5497,7 +5497,7 @@ int mas_preallocate(struct ma_state *mas, void *entry, gfp_t gfp)
/* At this point, we are at the leaf node that needs to be altered. */
/* Exact fit, no nodes needed. */
if (wr_mas.r_min == mas->index && wr_mas.r_max == mas->last)
return 0;
goto set_flag;
mas_wr_end_piv(&wr_mas);
node_size = mas_wr_new_end(&wr_mas);
@ -5506,10 +5506,10 @@ int mas_preallocate(struct ma_state *mas, void *entry, gfp_t gfp)
if (node_size == wr_mas.node_end) {
/* reuse node */
if (!mt_in_rcu(mas->tree))
return 0;
goto set_flag;
/* shifting boundary */
if (wr_mas.offset_end - mas->offset == 1)
return 0;
goto set_flag;
}
if (node_size >= mt_slots[wr_mas.type]) {
@ -5528,10 +5528,13 @@ int mas_preallocate(struct ma_state *mas, void *entry, gfp_t gfp)
/* node store, slot store needs one node */
ask_now:
mas->mas_flags &= ~MA_STATE_PREALLOC;
mas_node_count_gfp(mas, request, gfp);
mas->mas_flags |= MA_STATE_PREALLOC;
if (likely(!mas_is_err(mas)))
if (likely(!mas_is_err(mas))) {
set_flag:
mas->mas_flags |= MA_STATE_PREALLOC;
return 0;
}
mas_set_alloc_req(mas, 0);
ret = xa_err(mas->node);