| From d0a3260511eb5d32af6cb96993ce28ddd5304a99 Mon Sep 17 00:00:00 2001 |
| From: Qian Cai <cai@lca.pw> |
| Date: Fri, 7 Feb 2020 09:29:11 -0500 |
| Subject: [PATCH] ext4: fix a data race in EXT4_I(inode)->i_disksize |
| |
| commit 35df4299a6487f323b0aca120ea3f485dfee2ae3 upstream. |
| |
| EXT4_I(inode)->i_disksize could be accessed concurrently as noticed by |
| KCSAN, |
| |
| BUG: KCSAN: data-race in ext4_write_end [ext4] / ext4_writepages [ext4] |
| |
| write to 0xffff91c6713b00f8 of 8 bytes by task 49268 on cpu 127: |
| ext4_write_end+0x4e3/0x750 [ext4] |
| ext4_update_i_disksize at fs/ext4/ext4.h:3032 |
| (inlined by) ext4_update_inode_size at fs/ext4/ext4.h:3046 |
| (inlined by) ext4_write_end at fs/ext4/inode.c:1287 |
| generic_perform_write+0x208/0x2a0 |
| ext4_buffered_write_iter+0x11f/0x210 [ext4] |
| ext4_file_write_iter+0xce/0x9e0 [ext4] |
| new_sync_write+0x29c/0x3b0 |
| __vfs_write+0x92/0xa0 |
| vfs_write+0x103/0x260 |
| ksys_write+0x9d/0x130 |
| __x64_sys_write+0x4c/0x60 |
| do_syscall_64+0x91/0xb47 |
| entry_SYSCALL_64_after_hwframe+0x49/0xbe |
| |
| read to 0xffff91c6713b00f8 of 8 bytes by task 24872 on cpu 37: |
| ext4_writepages+0x10ac/0x1d00 [ext4] |
| mpage_map_and_submit_extent at fs/ext4/inode.c:2468 |
| (inlined by) ext4_writepages at fs/ext4/inode.c:2772 |
| do_writepages+0x5e/0x130 |
| __writeback_single_inode+0xeb/0xb20 |
| writeback_sb_inodes+0x429/0x900 |
| __writeback_inodes_wb+0xc4/0x150 |
| wb_writeback+0x4bd/0x870 |
| wb_workfn+0x6b4/0x960 |
| process_one_work+0x54c/0xbe0 |
| worker_thread+0x80/0x650 |
| kthread+0x1e0/0x200 |
| ret_from_fork+0x27/0x50 |
| |
| Reported by Kernel Concurrency Sanitizer on: |
| CPU: 37 PID: 24872 Comm: kworker/u261:2 Tainted: G W O L 5.5.0-next-20200204+ #5 |
| Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019 |
| Workqueue: writeback wb_workfn (flush-7:0) |
| |
| Since only the read is operating as lockless (outside of the |
| "i_data_sem"), load tearing could introduce a logic bug. Fix it by |
| adding READ_ONCE() for the read and WRITE_ONCE() for the write. |
| |
| Signed-off-by: Qian Cai <cai@lca.pw> |
| Link: https://lore.kernel.org/r/1581085751-31793-1-git-send-email-cai@lca.pw |
| Signed-off-by: Theodore Ts'o <tytso@mit.edu> |
| Cc: stable@kernel.org |
| Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> |
| |
| diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h |
| index 9393553cbbbf..67b3c9218abe 100644 |
| --- a/fs/ext4/ext4.h |
| +++ b/fs/ext4/ext4.h |
| @@ -2938,7 +2938,7 @@ static inline void ext4_update_i_disksize(struct inode *inode, loff_t newsize) |
| !inode_is_locked(inode)); |
| down_write(&EXT4_I(inode)->i_data_sem); |
| if (newsize > EXT4_I(inode)->i_disksize) |
| - EXT4_I(inode)->i_disksize = newsize; |
| + WRITE_ONCE(EXT4_I(inode)->i_disksize, newsize); |
| up_write(&EXT4_I(inode)->i_data_sem); |
| } |
| |
| diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c |
| index 8b46f8e259bf..16ab90172805 100644 |
| --- a/fs/ext4/inode.c |
| +++ b/fs/ext4/inode.c |
| @@ -2591,7 +2591,7 @@ static int mpage_map_and_submit_extent(handle_t *handle, |
| * truncate are avoided by checking i_size under i_data_sem. |
| */ |
| disksize = ((loff_t)mpd->first_page) << PAGE_SHIFT; |
| - if (disksize > EXT4_I(inode)->i_disksize) { |
| + if (disksize > READ_ONCE(EXT4_I(inode)->i_disksize)) { |
| int err2; |
| loff_t i_size; |
| |
| -- |
| 2.7.4 |
| |