From e3fea3f70fd68af0574a5f24246cdb4ed07f2b74 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Sat, 9 Jun 2012 08:15:16 +0100 Subject: [PATCH] selinux: fix selinux_inode_setxattr oops 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() Cc: stable@vger.kernel.org Signed-off-by: Al Viro Tested-by: Dave Jones Reported-by: Dave Jones Signed-off-by: James Morris --- security/selinux/hooks.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 94c45a1..79690f4 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -2791,11 +2791,16 @@ static int selinux_inode_setxattr(struct dentry *dentry, const char *name, /* 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); -- 2.7.4