From: Uladzislau Rezki <uladzislau.rezki@xxxxxxxx>
free_handle() for a foreign handle may race with inter-page
compaction, what can lead to memory corruption. To avoid that,
take write lock not read lock in free_handle to be synchronized
with __release_z3fold_page().
For example KASAN can detect it:
[ 33.723357] ==================================================================
[ 33.723401] BUG: KASAN: use-after-free in LZ4_decompress_safe+0x2c4/0x3b8
[ 33.723418] Read of size 1 at addr ffffffc976695ca3 by task GoogleApiHandle/4121
[ 33.723428]
[ 33.723449] CPU: 0 PID: 4121 Comm: GoogleApiHandle Tainted: P S OE 4.19.81-perf+ #162
[ 33.723461] Hardware name: Sony Mobile Communications. PDX-203(KONA) (DT)
[ 33.723473] Call trace:
[ 33.723495] dump_backtrace+0x0/0x288
[ 33.723512] show_stack+0x14/0x20
[ 33.723533] dump_stack+0xe4/0x124
[ 33.723551] print_address_description+0x80/0x2e0
[ 33.723566] kasan_report+0x268/0x2d0
[ 33.723584] __asan_load1+0x4c/0x58
[ 33.723601] LZ4_decompress_safe+0x2c4/0x3b8
[ 33.723619] lz4_decompress_crypto+0x3c/0x70
[ 33.723636] crypto_decompress+0x58/0x70
[ 33.723656] zcomp_decompress+0xd4/0x120
...
Apart from that, initialize zhdr->mapped_count in init_z3fold_page()
and remove "newpage" variable because it is not used anywhere.
Signed-off-by: Uladzislau Rezki <uladzislau.rezki@xxxxxxxx>
Signed-off-by: Vitaly Wool <vitaly.wool@xxxxxxxxxxxx>
---
mm/z3fold.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/mm/z3fold.c b/mm/z3fold.c
index 42f31c4b53ad..8c3bb5e508b8 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -318,16 +318,16 @@ static inline void free_handle(unsigned long handle)
slots = handle_to_slots(handle);
write_lock(&slots->lock);
*(unsigned long *)handle = 0;
- write_unlock(&slots->lock);
- if (zhdr->slots == slots)
+ if (zhdr->slots == slots) {
+ write_unlock(&slots->lock);
return; /* simple case, nothing else to do */
+ }
/* we are freeing a foreign handle if we are here */
zhdr->foreign_handles--;
is_free = true;
- read_lock(&slots->lock);
if (!test_bit(HANDLES_ORPHANED, &slots->pool)) {
- read_unlock(&slots->lock);
+ write_unlock(&slots->lock);
return;
}
for (i = 0; i <= BUDDY_MASK; i++) {
@@ -336,7 +336,7 @@ static inline void free_handle(unsigned long handle)
break;
}
}
- read_unlock(&slots->lock);
+ write_unlock(&slots->lock);
if (is_free) {
struct z3fold_pool *pool = slots_to_pool(slots);
@@ -422,6 +422,7 @@ static struct z3fold_header *init_z3fold_page(struct page *page, bool headless,
zhdr->start_middle = 0;
zhdr->cpu = -1;
zhdr->foreign_handles = 0;
+ zhdr->mapped_count = 0;
zhdr->slots = slots;
zhdr->pool = pool;
INIT_LIST_HEAD(&zhdr->buddy);
--
2.20.1
