| From | Greg Kroah-Hartman <> | Subject | [ 06/82] selinux: fix selinux_inode_setxattr oops | Date | Mon, 13 Aug 2012 13:18:42 -0700 |
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From: Greg KH <gregkh@linuxfoundation.org>
3.5-stable review patch. If anyone has any objections, please let me know.
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From: Al Viro <viro@ZenIV.linux.org.uk>
commit e3fea3f70fd68af0574a5f24246cdb4ed07f2b74 upstream.
OK, what we have so far is e.g. setxattr(path, name, whatever, 0, XATTR_REPLACE) with name being good enough to get through xattr_permission(). Then we reach security_inode_setxattr() with the desired value and size. Aha. name should begin with "security.selinux", or we won't get that far in selinux_inode_setxattr(). Suppose we got there and have enough permissions to relabel that sucker. We call security_context_to_sid() with value == NULL, size == 0. OK, we want ss_initialized to be non-zero. I.e. after everything had been set up and running. No problem...
We do 1-byte kmalloc(), zero-length memcpy() (which doesn't oops, even thought the source is NULL) and put a NUL there. I.e. form an empty string. string_to_context_struct() is called and looks for the first ':' in there. Not found, -EINVAL we get. OK, security_context_to_sid_core() has rc == -EINVAL, force == 0, so it silently returns -EINVAL. All it takes now is not having CAP_MAC_ADMIN and we are fucked.
All right, it might be a different bug (modulo strange code quoted in the report), but it's real. Easily fixed, AFAICS:
Deal with size == 0, value == NULL case in selinux_inode_setxattr()
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Tested-by: Dave Jones <davej@redhat.com> Reported-by: Dave Jones <davej@redhat.com> Signed-off-by: James Morris <james.l.morris@oracle.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- security/selinux/hooks.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-)
--- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -2792,11 +2792,16 @@ static int selinux_inode_setxattr(struct /* We strip a nul only if it is at the end, otherwise the * context contains a nul and we should audit that */ - str = value; - if (str[size - 1] == '\0') - audit_size = size - 1; - else - audit_size = size; + if (value) { + str = value; + if (str[size - 1] == '\0') + audit_size = size - 1; + else + audit_size = size; + } else { + str = ""; + audit_size = 0; + } ab = audit_log_start(current->audit_context, GFP_ATOMIC, AUDIT_SELINUX_ERR); audit_log_format(ab, "op=setxattr invalid_context="); audit_log_n_untrustedstring(ab, value, audit_size);
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