From d8f117abb380ba968b5e3ef2042d901c02872a4c Mon Sep 17 00:00:00 2001 From: Uladzislau Rezki Date: Fri, 22 May 2020 22:23:12 -0700 Subject: z3fold: fix use-after-free when freeing handles 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: ================================================================== BUG: KASAN: use-after-free in LZ4_decompress_safe+0x2c4/0x3b8 Read of size 1 at addr ffffffc976695ca3 by task GoogleApiHandle/4121 CPU: 0 PID: 4121 Comm: GoogleApiHandle Tainted: P S OE 4.19.81-perf+ #162 Hardware name: Sony Mobile Communications. PDX-203(KONA) (DT) Call trace: LZ4_decompress_safe+0x2c4/0x3b8 lz4_decompress_crypto+0x3c/0x70 crypto_decompress+0x58/0x70 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 Signed-off-by: Vitaly Wool Signed-off-by: Andrew Morton Cc: Qian Cai Cc: Raymond Jennings Cc: Link: http://lkml.kernel.org/r/20200520082100.28876-1-vitaly.wool@konsulko.com Signed-off-by: Linus Torvalds --- mm/z3fold.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) (limited to 'mm/z3fold.c') 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); -- cgit