From d14f5efadd846dbde561bd734318de6a9e6b26e6 Mon Sep 17 00:00:00 2001 From: Luo Meng Date: Fri, 13 May 2022 10:52:25 +0800 Subject: [PATCH] tmpfs: fix undefined-behaviour in shmem_reconfigure() When shmem_reconfigure() calls __percpu_counter_compare(), the second parameter is unsigned long long. But in the definition of __percpu_counter_compare(), the second parameter is s64. So when __percpu_counter_compare() executes abs(count - rhs), UBSAN shows the following warning: ================================================================================ UBSAN: Undefined behaviour in lib/percpu_counter.c:209:6 signed integer overflow: 0 - -9223372036854775808 cannot be represented in type 'long long int' CPU: 1 PID: 9636 Comm: syz-executor.2 Tainted: G ---------r- - 4.18.0 #2 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014 Call Trace: __dump_stack home/install/linux-rh-3-10/lib/dump_stack.c:77 [inline] dump_stack+0x125/0x1ae home/install/linux-rh-3-10/lib/dump_stack.c:117 ubsan_epilogue+0xe/0x81 home/install/linux-rh-3-10/lib/ubsan.c:159 handle_overflow+0x19d/0x1ec home/install/linux-rh-3-10/lib/ubsan.c:190 __percpu_counter_compare+0x124/0x140 home/install/linux-rh-3-10/lib/percpu_counter.c:209 percpu_counter_compare home/install/linux-rh-3-10/./include/linux/percpu_counter.h:50 [inline] shmem_remount_fs+0x1ce/0x6b0 home/install/linux-rh-3-10/mm/shmem.c:3530 do_remount_sb+0x11b/0x530 home/install/linux-rh-3-10/fs/super.c:888 do_remount home/install/linux-rh-3-10/fs/namespace.c:2344 [inline] do_mount+0xf8d/0x26b0 home/install/linux-rh-3-10/fs/namespace.c:2844 ksys_mount+0xad/0x120 home/install/linux-rh-3-10/fs/namespace.c:3075 __do_sys_mount home/install/linux-rh-3-10/fs/namespace.c:3089 [inline] __se_sys_mount home/install/linux-rh-3-10/fs/namespace.c:3086 [inline] __x64_sys_mount+0xbf/0x160 home/install/linux-rh-3-10/fs/namespace.c:3086 do_syscall_64+0xca/0x5c0 home/install/linux-rh-3-10/arch/x86/entry/common.c:298 entry_SYSCALL_64_after_hwframe+0x6a/0xdf RIP: 0033:0x46b5e9 Code: 5d db fa ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 2b db fa ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007f54d5f22c68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5 RAX: ffffffffffffffda RBX: 000000000077bf60 RCX: 000000000046b5e9 RDX: 0000000000000000 RSI: 0000000020000000 RDI: 0000000000000000 RBP: 000000000077bf60 R08: 0000000020000140 R09: 0000000000000000 R10: 00000000026740a4 R11: 0000000000000246 R12: 0000000000000000 R13: 00007ffd1fb1592f R14: 00007f54d5f239c0 R15: 000000000077bf6c ================================================================================ [akpm@linux-foundation.org: tweak error message text] Link: https://lkml.kernel.org/r/20220513025225.2678727-1-luomeng12@huawei.com Signed-off-by: Luo Meng Cc: Hugh Dickins Cc: Yu Kuai Signed-off-by: Andrew Morton --- mm/shmem.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/shmem.c b/mm/shmem.c index 67a3f3b05fb2e4..7f41a24ed3820b 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -3476,6 +3476,10 @@ static int shmem_reconfigure(struct fs_context *fc) raw_spin_lock(&sbinfo->stat_lock); inodes = sbinfo->max_inodes - sbinfo->free_inodes; + if (ctx->blocks > S64_MAX) { + err = "Number of blocks too large"; + goto out; + } if ((ctx->seen & SHMEM_SEEN_BLOCKS) && ctx->blocks) { if (!sbinfo->max_blocks) { err = "Cannot retroactively limit size";