Messages in this thread | | | From | Andy Lutomirski <> | Date | Wed, 29 Oct 2014 09:23:45 -0700 | Subject | Re: [GIT PULL] Fix for Integrity subsystem null pointer deref |
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On Oct 29, 2014 6:00 AM, "Mimi Zohar" <zohar@linux.vnet.ibm.com> wrote: > > On Tue, 2014-10-28 at 22:08 -0700, Andy Lutomirski wrote: > > On Tue, Oct 28, 2014 at 8:55 PM, James Morris <jmorris@namei.org> wrote: > > > These changes fix a bug in xattr handling, where the evm and ima > > > inode_setxattr() functions do not check for empty xattrs being passed from > > > userspace (leading to user-triggerable null pointer dereferences). > > > > > > Please pull. > > > > > > > > > The following changes since commit 9f76628da20f96a179ca62b504886f99ecc29223: > > > > > > Merge branch 'for-3.18' of git://linux-nfs.org/~bfields/linux (2014-10-28 13:32:06 -0700) > > > > > > are available in the git repository at: > > > > > > git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security.git for-linus > > > > > > Dmitry Kasatkin (2): > > > ima: check xattr value length and type in the ima_inode_setxattr() > > > > I haven't read this one, but: > > > > > evm: check xattr value length and type in evm_inode_setxattr() > > > > const struct evm_ima_xattr_data *xattr_data = xattr_value; > > - if ((strcmp(xattr_name, XATTR_NAME_EVM) == 0) > > - && (xattr_data->type == EVM_XATTR_HMAC)) > > - return -EPERM; > > + if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) { > > + if (!xattr_value_len) > > + return -EINVAL; > > + if (xattr_data->type != EVM_IMA_XATTR_DIGSIG) > > + return -EPERM; > > + } > > > > Huh? (Sorry about severe whitespace damage.) > > > > Shouldn't there be something like if (xattr_value_len < sizeof(struct > > evm_ima_xattr_data)) return -EINVAL? > > Prior to commit 2fb1c9a "evm: prohibit userspace writing 'security.evm' > HMAC value", a process with CAP_SYS_ADMIN could write either an HMAC or > signature. As the HMAC key should only be known to the kernel, only > signatures are now allowed. Instead of "struct evm_ima_xattr_data", the > code should reflect this change and use "struct signature_v2_hdr". > We'll clean up this code for the next release. For now, this patch > prevents the oops. >
I have no idea what the semantics are. All I'm saying is that it looks like the code still accesses memory past the end of the buffer. The buffer isn't a null pointer, so the symptom is different, but it may still be a security bug.
--Andy
> thanks, > > Mimi >
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