This is a note to let you know that I've just added the patch titled
maple_tree: disable mas_wr_append() when other readers are possible
to the 6.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
maple_tree-disable-mas_wr_append-when-other-readers-.patch
and it can be found in the queue-6.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit b91c7f43cef8824a77b803702f2695119b451470
Author: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Date: Fri Aug 18 20:43:55 2023 -0400
maple_tree: disable mas_wr_append() when other readers are possible
[ Upstream commit cfeb6ae8bcb96ccf674724f223661bbcef7b0d0b ]
The current implementation of append may cause duplicate data and/or
incorrect ranges to be returned to a reader during an update. Although
this has not been reported or seen, disable the append write operation
while the tree is in rcu mode out of an abundance of caution.
During the analysis of the mas_next_slot() the following was
artificially created by separating the writer and reader code:
Writer: reader:
mas_wr_append
set end pivot
updates end metata
Detects write to last slot
last slot write is to start of slot
store current contents in slot
overwrite old end pivot
mas_next_slot():
read end metadata
read old end pivot
return with incorrect range
store new value
Alternatively:
Writer: reader:
mas_wr_append
set end pivot
updates end metata
Detects write to last slot
last lost write to end of slot
store value
mas_next_slot():
read end metadata
read old end pivot
read new end pivot
return with incorrect range
set old end pivot
There may be other accesses that are not safe since we are now updating
both metadata and pointers, so disabling append if there could be rcu
readers is the safest action.
Link: https://lkml.kernel.org/r/20230819004356.1454718-2-Liam.Howlett@xxxxxxxxxx
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index bb28a49d173c0..3315eaf93f563 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -4315,6 +4315,9 @@ static inline bool mas_wr_append(struct ma_wr_state *wr_mas)
struct ma_state *mas = wr_mas->mas;
unsigned char node_pivots = mt_pivots[wr_mas->type];
+ if (mt_in_rcu(mas->tree))
+ return false;
+
if ((mas->index != wr_mas->r_min) && (mas->last == wr_mas->r_max)) {
if (new_end < node_pivots)
wr_mas->pivots[new_end] = wr_mas->pivots[end];
