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authorQian Cai <cai@lca.pw>2020-02-07 09:29:11 -0500
committerTheodore Ts'o <tytso@mit.edu>2020-02-19 23:17:02 -0500
commit35df4299a6487f323b0aca120ea3f485dfee2ae3 (patch)
treead8e53b8614db559a15d9c05d3b163b0091f2c3b
parent11a48a5a18c63fd7621bb050228cebf13566e4d8 (diff)
downloadlinux-35df4299a6487f323b0aca120ea3f485dfee2ae3.tar.bz2
ext4: fix a data race in EXT4_I(inode)->i_disksize
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
-rw-r--r--fs/ext4/ext4.h2
-rw-r--r--fs/ext4/inode.c2
2 files changed, 2 insertions, 2 deletions
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 4441331d06cc..480badcf2783 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -3032,7 +3032,7 @@ 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 e60aca791d3f..6e1d81ed44ad 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2465,7 +2465,7 @@ update_disksize:
* 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;