On Thu, Jun 4, 2015 at 5:32 PM, Jan Kara <j...@suse.cz> wrote: > On Thu 04-06-15 09:18:49, Paul Moore wrote: >> On Thu, Jun 4, 2015 at 3:36 AM, Jan Kara <j...@suse.cz> wrote: >> > On Wed 03-06-15 14:56:18, Paul Moore wrote: >> >> On Tuesday, June 02, 2015 05:08:29 PM Jan Kara wrote: >> >> > strnlen_user() returns 0 when it hits fault, not -1. Fix the test in >> >> > audit_log_single_execve_arg(). Luckily this shouldn't ever happen unless >> >> > there's a kernel bug so it's mostly a cosmetic fix. >> >> > >> >> > CC: Paul Moore <pmo...@redhat.com> >> >> > Signed-off-by: Jan Kara <j...@suse.cz> >> >> > --- >> >> > kernel/auditsc.c | 2 +- >> >> > 1 file changed, 1 insertion(+), 1 deletion(-) >> >> > >> >> > diff --git a/kernel/auditsc.c b/kernel/auditsc.c >> >> > index 9fb9d1cb83ce..bb947ceeee4d 100644 >> >> > --- a/kernel/auditsc.c >> >> > +++ b/kernel/auditsc.c >> >> > @@ -1023,7 +1023,7 @@ static int audit_log_single_execve_arg(struct >> >> > audit_context *context, * for strings that are too long, we should not >> >> > have >> >> > created >> >> > * any. >> >> > */ >> >> > - if (unlikely((len == -1) || len > MAX_ARG_STRLEN - 1)) { >> >> > + if (unlikely((len == 0) || len > MAX_ARG_STRLEN - 1)) { >> >> >> >> While we're at it, should we make it just "len > MAX_ARG_STRLEN" as well? >> >> Reading the comments in include/uapi/linux/binfmts.h as well as >> >> valid_arg_len() that seems to be the correct logic. >> > >> > Umm, but audit_log_single_execve_arg() does decrement 1 from >> > strnlen_user() result before doing the comparison. So the current test >> > seems to match the one in valid_arg_len() exactly... >> >> For reference (taken from fs/exec.c in Linus' tree just now): >> >> static bool valid_arg_len(struct linux_binprm *bprm, long len) >> { >> return len <= MAX_ARG_STRLEN; >> } >> >> The valid_arg_len() returns true when the length is less than or equal >> to MAX_ARG_STRLEN, implying that lengths greater than MAX_ARG_STRLEN >> are invalid. The existing test in audit_log_single_execve_arg() >> treats lengths greater than (MAX_ARG_STRLEN-1) as invalid. > But the 'len' passed to valid_arg_len() is the return value of > strnlen_user() and that one returns lenght *including* the terminating > '\0'. So in fact valid_arg_len() tests whether the argument length is <= > (MAX_ARG_STRLEN-1). Hmm?
I must have spaced on the fact that audit subtracts the NULL from the output of strnlen_user() when it calls it earlier in the function. -- paul moore www.paul-moore.com -- Linux-audit mailing list Linux-audit@redhat.com https://www.redhat.com/mailman/listinfo/linux-audit