Re: [PATCH 1/1] Fix memory leak in kernfs_security_xattr_set and kernfs_security_xattr_set

From: Casey Schaufler <casey@schaufler-ca.com>
To: CHANDAN VN <chandan.vn@samsung.com>,
	gregkh@linuxfoundation.org, tj@kernel.org, bfields@fieldses.org,
	jlayton@kernel.org, linux-kernel@vger.kernel.org,
	linux-nfs@vger.kernel.org
Cc: cpgs@samsung.com, sireesha.t@samsung.com,
	Casey Schaufler <casey@schaufler-ca.com>
Subject: Re: [PATCH 1/1] Fix memory leak in kernfs_security_xattr_set and kernfs_security_xattr_set
Date: Thu, 31 May 2018 08:26:23 -0700	[thread overview]
Message-ID: <cae274dd-e9e5-39b1-8b7b-aec1b3e76fe9@schaufler-ca.com> (raw)
In-Reply-To: <1527758911-18610-1-git-send-email-chandan.vn@samsung.com>

On 5/31/2018 2:28 AM, CHANDAN VN wrote:
> From: "sireesha.t" <sireesha.t@samsung.com>
>
> Leak is caused because smack_inode_getsecurity() is allocating memory
> using kstrdup(). Though the security_release_secctx() is called, it
> would not free the allocated memory. Calling security_release_secctx is
> not relevant for this scenario as inode_getsecurity() does not provide a
> "secctx".
>
> Similar fix has been mainlined:
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/?id=57e7ba04d422c3d41c8426380303ec9b7533ded9
>
> The fix is to replace the security_release_secctx() with a kfree()
>
> Below is the KMEMLEAK dump:
> unreferenced object 0xffffffc025e11c80 (size 64):
>   comm "systemd-tmpfile", pid 2452, jiffies 4294894464 (age 235587.492s)
>   hex dump (first 32 bytes):
>     53 79 73 74 65 6d 3a 3a 53 68 61 72 65 64 00 00  System::Shared..
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>   backtrace:
>     [<ffffff80081be770>] __save_stack_trace+0x28/0x34
>     [<ffffff80081bedb8>] create_object+0x130/0x25c
>     [<ffffff80088c82f8>] kmemleak_alloc+0x30/0x5c
>     [<ffffff80081b3ef0>] __kmalloc_track_caller+0x1cc/0x2a8
>     [<ffffff800818673c>] kstrdup+0x3c/0x6c
>     [<ffffff80082d78b0>] smack_inode_getsecurity+0xcc/0xec
>     [<ffffff80082d78f4>] smack_inode_getsecctx+0x24/0x44
>     [<ffffff80082d5ea0>] security_inode_getsecctx+0x50/0x70
>     [<ffffff800823bbcc>] kernfs_security_xattr_set+0x74/0xe0
>     [<ffffff80081eafec>] __vfs_setxattr+0x74/0x90
>     [<ffffff80081eb088>] __vfs_setxattr_noperm+0x80/0x1ac
>     [<ffffff80081eb238>] vfs_setxattr+0x84/0xac
>     [<ffffff80081eb374>] setxattr+0x114/0x178
>     [<ffffff80081eb44c>] path_setxattr+0x74/0xb8
>     [<ffffff80081ebdcc>] SyS_lsetxattr+0x10/0x1c
>     [<ffffff800808310c>] __sys_trace_return+0x0/0x4
>
> Signed-off-by: sireesha.t <sireesha.t@samsung.com>
> Signed-off-by: CHANDAN VN <chandan.vn@samsung.com>

Why not:

 static int smack_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen)
 {
-	int len = 0;
-	len = smack_inode_getsecurity(inode, XATTR_SMACK_SUFFIX, ctx, true);
+	int len = smack_inode_getsecurity(inode, XATTR_SMACK_SUFFIX, ctx, false);

 	if (len < 0)
 		return len;

> ---
>  fs/kernfs/inode.c | 3 ++-
>  fs/nfsd/nfs4xdr.c | 2 +-
>  2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
> index a343039..53befb8 100644
> --- a/fs/kernfs/inode.c
> +++ b/fs/kernfs/inode.c
> @@ -369,7 +369,8 @@ static int kernfs_security_xattr_set(const struct xattr_handler *handler,
>  	mutex_unlock(&kernfs_mutex);
>  
>  	if (secdata)
> -		security_release_secctx(secdata, secdata_len);
> +		kfree(secdata);
> +
>  	return error;
>  }
>  
> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> index aaa88c1..1e0dbe9 100644
> --- a/fs/nfsd/nfs4xdr.c
> +++ b/fs/nfsd/nfs4xdr.c
> @@ -2911,7 +2911,7 @@ static int get_parent_attributes(struct svc_export *exp, struct kstat *stat)
>  out:
>  #ifdef CONFIG_NFSD_V4_SECURITY_LABEL
>  	if (context)
> -		security_release_secctx(context, contextlen);
> +		kfree(context);
>  #endif /* CONFIG_NFSD_V4_SECURITY_LABEL */
>  	kfree(acl);
>  	if (tempfh) {