The patch titled
Subject: mm: kmem: fix a NULL pointer dereference in obj_stock_flush_required()
has been added to the -mm mm-unstable branch. Its filename is
mm-kmem-fix-a-null-pointer-dereference-in-obj_stock_flush_required.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-kmem-fix-a-null-pointer-dereference-in-obj_stock_flush_required.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Subject: mm: kmem: fix a NULL pointer dereference in obj_stock_flush_required()
Date: Tue, 2 May 2023 09:08:38 -0700
KCSAN found an issue in obj_stock_flush_required():
stock->cached_objcg can be reset between the check and dereference:
==================================================================
BUG: KCSAN: data-race in drain_all_stock / drain_obj_stock
write to 0xffff888237c2a2f8 of 8 bytes by task 19625 on cpu 0:
drain_obj_stock+0x408/0x4e0 mm/memcontrol.c:3306
refill_obj_stock+0x9c/0x1e0 mm/memcontrol.c:3340
obj_cgroup_uncharge+0xe/0x10 mm/memcontrol.c:3408
memcg_slab_free_hook mm/slab.h:587 [inline]
__cache_free mm/slab.c:3373 [inline]
__do_kmem_cache_free mm/slab.c:3577 [inline]
kmem_cache_free+0x105/0x280 mm/slab.c:3602
__d_free fs/dcache.c:298 [inline]
dentry_free fs/dcache.c:375 [inline]
__dentry_kill+0x422/0x4a0 fs/dcache.c:621
dentry_kill+0x8d/0x1e0
dput+0x118/0x1f0 fs/dcache.c:913
__fput+0x3bf/0x570 fs/file_table.c:329
____fput+0x15/0x20 fs/file_table.c:349
task_work_run+0x123/0x160 kernel/task_work.c:179
resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
exit_to_user_mode_loop+0xcf/0xe0 kernel/entry/common.c:171
exit_to_user_mode_prepare+0x6a/0xa0 kernel/entry/common.c:203
__syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
syscall_exit_to_user_mode+0x26/0x140 kernel/entry/common.c:296
do_syscall_64+0x4d/0xc0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x63/0xcd
read to 0xffff888237c2a2f8 of 8 bytes by task 19632 on cpu 1:
obj_stock_flush_required mm/memcontrol.c:3319 [inline]
drain_all_stock+0x174/0x2a0 mm/memcontrol.c:2361
try_charge_memcg+0x6d0/0xd10 mm/memcontrol.c:2703
try_charge mm/memcontrol.c:2837 [inline]
mem_cgroup_charge_skmem+0x51/0x140 mm/memcontrol.c:7290
sock_reserve_memory+0xb1/0x390 net/core/sock.c:1025
sk_setsockopt+0x800/0x1e70 net/core/sock.c:1525
udp_lib_setsockopt+0x99/0x6c0 net/ipv4/udp.c:2692
udp_setsockopt+0x73/0xa0 net/ipv4/udp.c:2817
sock_common_setsockopt+0x61/0x70 net/core/sock.c:3668
__sys_setsockopt+0x1c3/0x230 net/socket.c:2271
__do_sys_setsockopt net/socket.c:2282 [inline]
__se_sys_setsockopt net/socket.c:2279 [inline]
__x64_sys_setsockopt+0x66/0x80 net/socket.c:2279
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
value changed: 0xffff8881382d52c0 -> 0xffff888138893740
Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 19632 Comm: syz-executor.0 Not tainted 6.3.0-rc2-syzkaller-00387-g534293368afa #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
Fix it by using READ_ONCE()/WRITE_ONCE() for all accesses to
stock->cached_objcg.
Link: https://lkml.kernel.org/r/20230502160839.361544-1-roman.gushchin@xxxxxxxxx
Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API")
Signed-off-by: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Reported-by: syzbot+774c29891415ab0fd29d@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Link: https://lore.kernel.org/linux-mm/CACT4Y+ZfucZhM60YPphWiCLJr6+SGFhT+jjm8k1P-a_8Kkxsjg@xxxxxxxxxxxxxx/T/#t
Cc: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 19 ++++++++++---------
1 file changed, 10 insertions(+), 9 deletions(-)
--- a/mm/memcontrol.c~mm-kmem-fix-a-null-pointer-dereference-in-obj_stock_flush_required
+++ a/mm/memcontrol.c
@@ -3208,12 +3208,12 @@ void mod_objcg_state(struct obj_cgroup *
* accumulating over a page of vmstat data or when pgdat or idx
* changes.
*/
- if (stock->cached_objcg != objcg) {
+ if (READ_ONCE(stock->cached_objcg) != objcg) {
old = drain_obj_stock(stock);
obj_cgroup_get(objcg);
stock->nr_bytes = atomic_read(&objcg->nr_charged_bytes)
? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0;
- stock->cached_objcg = objcg;
+ WRITE_ONCE(stock->cached_objcg, objcg);
stock->cached_pgdat = pgdat;
} else if (stock->cached_pgdat != pgdat) {
/* Flush the existing cached vmstat data */
@@ -3267,7 +3267,7 @@ static bool consume_obj_stock(struct obj
local_lock_irqsave(&memcg_stock.stock_lock, flags);
stock = this_cpu_ptr(&memcg_stock);
- if (objcg == stock->cached_objcg && stock->nr_bytes >= nr_bytes) {
+ if (objcg == READ_ONCE(stock->cached_objcg) && stock->nr_bytes >= nr_bytes) {
stock->nr_bytes -= nr_bytes;
ret = true;
}
@@ -3279,7 +3279,7 @@ static bool consume_obj_stock(struct obj
static struct obj_cgroup *drain_obj_stock(struct memcg_stock_pcp *stock)
{
- struct obj_cgroup *old = stock->cached_objcg;
+ struct obj_cgroup *old = READ_ONCE(stock->cached_objcg);
if (!old)
return NULL;
@@ -3332,7 +3332,7 @@ static struct obj_cgroup *drain_obj_stoc
stock->cached_pgdat = NULL;
}
- stock->cached_objcg = NULL;
+ WRITE_ONCE(stock->cached_objcg, NULL);
/*
* The `old' objects needs to be released by the caller via
* obj_cgroup_put() outside of memcg_stock_pcp::stock_lock.
@@ -3343,10 +3343,11 @@ static struct obj_cgroup *drain_obj_stoc
static bool obj_stock_flush_required(struct memcg_stock_pcp *stock,
struct mem_cgroup *root_memcg)
{
+ struct obj_cgroup *objcg = READ_ONCE(stock->cached_objcg);
struct mem_cgroup *memcg;
- if (stock->cached_objcg) {
- memcg = obj_cgroup_memcg(stock->cached_objcg);
+ if (objcg) {
+ memcg = obj_cgroup_memcg(objcg);
if (memcg && mem_cgroup_is_descendant(memcg, root_memcg))
return true;
}
@@ -3365,10 +3366,10 @@ static void refill_obj_stock(struct obj_
local_lock_irqsave(&memcg_stock.stock_lock, flags);
stock = this_cpu_ptr(&memcg_stock);
- if (stock->cached_objcg != objcg) { /* reset if necessary */
+ if (READ_ONCE(stock->cached_objcg) != objcg) { /* reset if necessary */
old = drain_obj_stock(stock);
obj_cgroup_get(objcg);
- stock->cached_objcg = objcg;
+ WRITE_ONCE(stock->cached_objcg, objcg);
stock->nr_bytes = atomic_read(&objcg->nr_charged_bytes)
? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0;
allow_uncharge = true; /* Allow uncharge when objcg changes */
_
Patches currently in -mm which might be from roman.gushchin@xxxxxxxxx are
mm-kmem-fix-a-null-pointer-dereference-in-obj_stock_flush_required.patch
mm-memcg-use-read_once-write_once-to-access-stock-cached.patch
