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authorOGAWA Hirofumi <hirofumi@mail.parknet.co.jp>2019-09-23 15:32:53 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2019-09-24 15:54:06 -0700
commit07bfa4415ab607e459b69bd86aa7e7602ce10b4f (patch)
tree62a7bc60deca51a1a795c8a22293e658d88efc07 /fs/fat/fatent.c
parent619e17cf75dd58905aa67ccd494a6ba5f19d6cc6 (diff)
fat: work around race with userspace's read via blockdev while mounting
If userspace reads the buffer via blockdev while mounting, sb_getblk()+modify can race with buffer read via blockdev. For example, FS userspace bh = sb_getblk() modify bh->b_data read ll_rw_block(bh) fill bh->b_data by on-disk data /* lost modified data by FS */ set_buffer_uptodate(bh) set_buffer_uptodate(bh) Userspace should not use the blockdev while mounting though, the udev seems to be already doing this. Although I think the udev should try to avoid this, workaround the race by small overhead. Link: http://lkml.kernel.org/r/87pnk7l3sw.fsf_-_@mail.parknet.co.jp Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Reported-by: Jan Stancek <jstancek@redhat.com> Tested-by: Jan Stancek <jstancek@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/fat/fatent.c')
-rw-r--r--fs/fat/fatent.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/fs/fat/fatent.c b/fs/fat/fatent.c
index 265983635f2b..3647c65a0f48 100644
--- a/fs/fat/fatent.c
+++ b/fs/fat/fatent.c
@@ -388,8 +388,11 @@ static int fat_mirror_bhs(struct super_block *sb, struct buffer_head **bhs,
err = -ENOMEM;
goto error;
}
+ /* Avoid race with userspace read via bdev */
+ lock_buffer(c_bh);
memcpy(c_bh->b_data, bhs[n]->b_data, sb->s_blocksize);
set_buffer_uptodate(c_bh);
+ unlock_buffer(c_bh);
mark_buffer_dirty_inode(c_bh, sbi->fat_inode);
if (sb->s_flags & SB_SYNCHRONOUS)
err = sync_dirty_buffer(c_bh);