[PATCH v1 2/4] ext4: fix race between llseek SEEK_END and write

Eiichi Tsukata
2018-11-21T02:43:58Z

Implement individual lock for SEEK_END for ext4 which directly calls
generic_file_llseek_size().

Signed-off-by: Eiichi Tsukata <devel@etsukata.com>
---
fs/ext4/file.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 69d65d49837b..6479f3066043 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -477,6 +477,16 @@ loff_t ext4_llseek(struct file *file, loff_t offset, int whence)
default:
return generic_file_llseek_size(file, offset, whence,
maxbytes, i_size_read(inode));
+ case SEEK_END:
+ /*
+ * protects against inode size race with write so that llseek
+ * doesn't see inode size being updated in generic_perform_write
+ */
+ inode_lock_shared(inode);
+ offset = generic_file_llseek_size(file, offset, whence,
+ maxbytes, i_size_read(inode));
+ inode_unlock_shared(inode);
+ return offset;
case SEEK_HOLE:
inode_lock_shared(inode);
offset = iomap_seek_hole(inode, offset, &ext4_iomap_ops);
--
2.19.1