From 500cac3ccee65526d5075da3af2674101305bf8c Mon Sep 17 00:00:00 2001 From: Vivek Goyal Date: Wed, 13 Jul 2016 11:00:14 -0400 Subject: [PATCH] ovl: append MAY_READ when diluting write checks Right now we remove MAY_WRITE/MAY_APPEND bits from mask if realfile is on lower/. This is done as files on lower will never be written and will be copied up. But to copy up a file, mounter should have MAY_READ permission otherwise copy up will fail. So set MAY_READ in mask when MAY_WRITE is reset. Dan Walsh noticed this when he did access(lowerfile, W_OK) and it returned True (context mounts) but when he tried to actually write to file, it failed as mounter did not have permission on lower file. [SzM] don't set MAY_READ if only MAY_APPEND is set without MAY_WRITE; this won't trigger a copy-up. Reported-by: Dan Walsh Signed-off-by: Vivek Goyal Signed-off-by: Miklos Szeredi --- fs/overlayfs/inode.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c index 76cfe9d04e64..1b885c156028 100644 --- a/fs/overlayfs/inode.c +++ b/fs/overlayfs/inode.c @@ -137,8 +137,11 @@ int ovl_permission(struct inode *inode, int mask) return err; old_cred = ovl_override_creds(inode->i_sb); - if (!is_upper && !special_file(realinode->i_mode)) + if (!is_upper && !special_file(realinode->i_mode) && mask & MAY_WRITE) { mask &= ~(MAY_WRITE | MAY_APPEND); + /* Make sure mounter can read file for copy up later */ + mask |= MAY_READ; + } err = inode_permission(realinode, mask); revert_creds(old_cred);