ext4: avoid setting directory i_nlink to zero
If a directory with more than EXT4_LINK_MAX subdirectories, the nlink
count is set to 1. Subsequently, if any subdirectories are deleted,
ext4_dec_count() decrements the i_nlink count, which may go to 0
temporarily before being incremented back to 1.
While this is done under i_mutex, which prevents races for directory
and inode operations that check i_nlink, the temporary i_nlink == 0
case is exposed to userspace via stat() and similar calls that do not
hold i_mutex.
Instead, change the code to not decrement i_nlink count for any
directories that do not already have i_nlink larger than 2.
Reported-by: Cliff White <cliffw@whamcloud.com>
Reviewed-by: Johann Lombardi <johann@whamcloud.com>
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index a067835..4a550aa 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -1706,9 +1706,8 @@
*/
static void ext4_dec_count(handle_t *handle, struct inode *inode)
{
- drop_nlink(inode);
- if (S_ISDIR(inode->i_mode) && inode->i_nlink == 0)
- inc_nlink(inode);
+ if (!S_ISDIR(inode->i_mode) || inode->i_nlink > 2)
+ drop_nlink(inode);
}