Hi Colin,
On Sun, 2018-05-27 at 23:55 +0100, Colin King wrote:
> From: Colin Ian King <colin.k...@canonical.com>
>
> In the case where the allocation of xattr fails and xattr is NULL, the
> error exit return path via label 'out' will dereference xattr when
> kfree'ing xattr-name. Fix this by only kfree'ing xattr->name and xattr
> when xattr is non-null.
>
> Detected by CoverityScan, CID#1469366 ("Dereference after null check")
>
> Fixes: fa516b66a1bf ("EVM: Allow runtime modification of the set of verified
> xattrs")
> Signed-off-by: Colin Ian King <colin.k...@canonical.com>
> ---
> security/integrity/evm/evm_secfs.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/security/integrity/evm/evm_secfs.c
> b/security/integrity/evm/evm_secfs.c
> index fb8bc950aceb..cf5cd303d7c0 100644
> --- a/security/integrity/evm/evm_secfs.c
> +++ b/security/integrity/evm/evm_secfs.c
> @@ -253,8 +253,10 @@ static ssize_t evm_write_xattrs(struct file *file, const
> char __user *buf,
> out:
> audit_log_format(ab, " res=%d", err);
> audit_log_end(ab);
> - kfree(xattr->name);
> - kfree(xattr);
> + if (xattr) {
> + kfree(xattr->name);
> + kfree(xattr);
> + }
> return err;
> }
>
Thanks! To fix this problem, I think more is needed.
Without the xattr, there is nothing to audit except the attempt to
extend the xattr list. Failure to allocate the xattr or xattr->name
should either result in a different audit message or return
immediately without any audit message.
Mimi
