Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932067AbaJXOWq (ORCPT ); Fri, 24 Oct 2014 10:22:46 -0400 Received: from e39.co.us.ibm.com ([32.97.110.160]:46986 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751729AbaJXOWo (ORCPT ); Fri, 24 Oct 2014 10:22:44 -0400 Message-ID: <1414160329.2120.30.camel@dhcp-9-2-203-236.watson.ibm.com> Subject: Re: [PATCH v2 1/2] ima: check xattr value length in ima_inode_setxattr() From: Mimi Zohar To: Dmitry Kasatkin Cc: linux-security-module@vger.kernel.org, linux-ima-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, jack@suse.cz, jmorris@namei.org, dmitry.kasatkin@gmail.com Date: Fri, 24 Oct 2014 10:18:49 -0400 In-Reply-To: <53afed717c1dc6b3588cca7c0a6b69650edc2ad2.1414134113.git.d.kasatkin@samsung.com> References: <53afed717c1dc6b3588cca7c0a6b69650edc2ad2.1414134113.git.d.kasatkin@samsung.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.6.4 (3.6.4-3.fc18) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14102414-0033-0000-0000-00000273D413 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2014-10-24 at 10:07 +0300, Dmitry Kasatkin wrote: > ima_inode_setxattr() can be called with no value. Function does not > check the length so that following command can be used to produce > kernel oops: setfattr -n security.ima FOO. This patch fixes it. > > Changes in v2: > * testing validity of xattr type > * allow setting hash only in fix or log mode (Mimi) I only mentioned "fix" mode, not "log" mode (explanation below). > > [ 261.562522] BUG: unable to handle kernel NULL pointer dereference at (null) > [ 261.564109] IP: [] ima_inode_setxattr+0x3e/0x5a > [ 261.564109] PGD 3112f067 PUD 42965067 PMD 0 > [ 261.564109] Oops: 0000 [#1] SMP > [ 261.564109] Modules linked in: bridge stp llc evdev serio_raw i2c_piix4 button fuse > [ 261.564109] CPU: 0 PID: 3299 Comm: setxattr Not tainted 3.16.0-kds+ #2924 > [ 261.564109] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 > [ 261.564109] task: ffff8800428c2430 ti: ffff880042be0000 task.ti: ffff880042be0000 > [ 261.564109] RIP: 0010:[] [] ima_inode_setxattr+0x3e/0x5a > [ 261.564109] RSP: 0018:ffff880042be3d50 EFLAGS: 00010246 > [ 261.564109] RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000015 > [ 261.564109] RDX: 0000001500000000 RSI: 0000000000000000 RDI: ffff8800375cc600 > [ 261.564109] RBP: ffff880042be3d68 R08: 0000000000000000 R09: 00000000004d6256 > [ 261.564109] R10: 0000000000000000 R11: 0000000000000000 R12: ffff88002149ba00 > [ 261.564109] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 > [ 261.564109] FS: 00007f6c1e219740(0000) GS:ffff88005da00000(0000) knlGS:0000000000000000 > [ 261.564109] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 261.564109] CR2: 0000000000000000 CR3: 000000003b35a000 CR4: 00000000000006f0 > [ 261.564109] Stack: > [ 261.564109] ffff88002149ba00 ffff880042be3df8 0000000000000000 ffff880042be3d98 > [ 261.564109] ffffffff812a101b ffff88002149ba00 ffff880042be3df8 0000000000000000 > [ 261.564109] 0000000000000000 ffff880042be3de0 ffffffff8116d08a ffff880042be3dc8 > [ 261.564109] Call Trace: > [ 261.564109] [] security_inode_setxattr+0x48/0x6a > [ 261.564109] [] vfs_setxattr+0x6b/0x9f > [ 261.564109] [] setxattr+0x122/0x16c > [ 261.564109] [] ? mnt_want_write+0x21/0x45 > [ 261.564109] [] ? __sb_start_write+0x10f/0x143 > [ 261.564109] [] ? mnt_want_write+0x21/0x45 > [ 261.564109] [] ? __mnt_want_write+0x48/0x4f > [ 261.564109] [] SyS_setxattr+0x6e/0xb0 > [ 261.564109] [] system_call_fastpath+0x16/0x1b > [ 261.564109] Code: 48 89 f7 48 c7 c6 58 36 81 81 53 31 db e8 73 27 04 00 85 c0 75 28 bf 15 00 00 00 e8 8a a5 d9 ff 84 c0 75 05 83 cb ff eb 15 31 f6 <41> 80 7d 00 03 49 8b 7c 24 68 40 0f 94 c6 e8 e1 f9 ff ff 89 d8 > [ 261.564109] RIP [] ima_inode_setxattr+0x3e/0x5a > [ 261.564109] RSP > [ 261.564109] CR2: 0000000000000000 > [ 261.599998] ---[ end trace 39a89a3fc267e652 ]--- > > Reported-by: Jan Kara > Signed-off-by: Dmitry Kasatkin > --- > security/integrity/ima/ima_appraise.c | 13 +++++++++++-- > 1 file changed, 11 insertions(+), 2 deletions(-) > > diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c > index 9226854..e302cbf 100644 > --- a/security/integrity/ima/ima_appraise.c > +++ b/security/integrity/ima/ima_appraise.c > @@ -378,8 +378,17 @@ int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name, > result = ima_protect_xattr(dentry, xattr_name, xattr_value, > xattr_value_len); > if (result == 1) { > - ima_reset_appraise_flags(dentry->d_inode, > - (xvalue->type == EVM_IMA_XATTR_DIGSIG) ? 1 : 0); > + bool digsig; > + > + if (!xattr_value_len || > + (xvalue->type != IMA_XATTR_DIGEST && > + xvalue->type != IMA_XATTR_DIGEST_NG && > + xvalue->type != EVM_IMA_XATTR_DIGSIG)) "xvalue->type" is an enumerated type. Testing each possible value seems kind of a brittle method for vetting the value. I suggest testing the existing last value or, better yet, define a last value, so if someone adds or changes the order, nothing breaks. > + return -EINVAL; > + digsig = (xvalue->type == EVM_IMA_XATTR_DIGSIG); > + if (!digsig && (ima_appraise & IMA_APPRAISE_ENFORCE)) > + return -EPERM; According to the new ima_appraise "log" mode, commit "2faa6ef ima: provide 'ima_appraise=log' kernel option", "log" mode permits normal execution without "fixing" anything. Normal execution, here, prevents writing the extended attribute. Mimi > + ima_reset_appraise_flags(dentry->d_inode, digsig); > result = 0; > } > return result; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/