[PATCH v1 4/4] overlayfs: fix race between llseek SEEK_END and write

Eiichi Tsukata
2018-11-21T02:44:00Z

Implement individual lock for SEEK_END for overlayfs which directly calls
generic_file_llseek_size().

Signed-off-by: Eiichi Tsukata <devel@etsukata.com>
---
fs/overlayfs/file.c | 23 ++++++++++++++++++++---
1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index 84dd957efa24..57bc6538eea8 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -146,10 +146,27 @@ static int ovl_release(struct inode *inode, struct file *file)
static loff_t ovl_llseek(struct file *file, loff_t offset, int whence)
{
struct inode *realinode = ovl_inode_real(file_inode(file));
+ loff_t ret;

- return generic_file_llseek_size(file, offset, whence,
- realinode->i_sb->s_maxbytes,
- i_size_read(realinode));
+ switch (whence) {
+ default:
+ return generic_file_llseek_size(file, offset, whence,
+ realinode->i_sb->s_maxbytes,
+ i_size_read(realinode));
+ case SEEK_END:
+ case SEEK_DATA:
+ case SEEK_HOLE:
+ /*
+ * protects against inode size race with write so that llseek
+ * doesn't see inode size being updated in individual fs write
+ */
+ inode_lock(realinode);
+ ret = generic_file_llseek_size(file, offset, whence,
+ realinode->i_sb->s_maxbytes,
+ i_size_read(realinode));
+ inode_unlock(realinode);
+ return ret;
+ }
}

static void ovl_file_accessed(struct file *file)
--
2.19.1