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Commit 500cac3c authored by Vivek Goyal's avatar Vivek Goyal Committed by Miklos Szeredi
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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: default avatarDan Walsh <dwalsh@redhat.com>
Signed-off-by: default avatarVivek Goyal <vgoyal@redhat.com>
Signed-off-by: default avatarMiklos Szeredi <mszeredi@redhat.com>
parent e29841a0

fs/overlayfs/inode.c

+4 −1
Original line number Diff line number Diff line
@@ -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);