Messages in this thread | | | Date | Thu, 24 Jan 2019 10:43:22 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH v2 1/3] tracing: uprobes: Re-enable $comm support for uprobe events |
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On Wed, 23 Jan 2019 03:40:05 -0500 Steven Rostedt <rostedt@goodmis.org> wrote:
> On Fri, 18 Jan 2019 13:44:25 +0900 > Masami Hiramatsu <mhiramat@kernel.org> wrote: > > > Since commit 533059281ee5 ("tracing: probeevent: Introduce new > > argument fetching code") dropped the $comm support from uprobe > > events, this re-enables it. > > > > For $comm support, uses strlcpy() instead of strncpy_from_user() > > to copy current task's comm. Because it is in the kernel space, > > strncpy_from_user() always fails to copy the comm. > > This also uses strlen() instead of strnlen_user() to measure the > > length of the comm. > > > > Fixes: 533059281ee5 ("tracing: probeevent: Introduce new argument fetching code") > > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> > > Reported-by: Andreas Ziegler <andreas.ziegler@fau.de> > > Acked-by: Andreas Ziegler <andreas.ziegler@fau.de> > > --- > > kernel/trace/trace_uprobe.c | 15 +++++++++++++-- > > 1 file changed, 13 insertions(+), 2 deletions(-) > > > > diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c > > index 3a1d5ab6b4ba..b07e498ccbc6 100644 > > --- a/kernel/trace/trace_uprobe.c > > +++ b/kernel/trace/trace_uprobe.c > > @@ -156,7 +156,10 @@ fetch_store_string(unsigned long addr, void *dest, void *base) > > if (unlikely(!maxlen)) > > return -ENOMEM; > > > > - ret = strncpy_from_user(dst, src, maxlen); > > + if (addr == (unsigned long)current->comm) > > + ret = strlcpy(dst, current->comm, maxlen); > > As user space (although only root) defines the size of the event being > stored, and we could trick addr to be current->comm (although > difficult), we could possibly leak data if maxlen is > TASK_COMM_LEN. I > would feel better if we tested maxlen against TASK_COMM_LEN in this > case. > > if (maxlen > TASK_COMM_LEN) > maxlen = TASK_COMM_LEN; > > Or if we don't think it can happen, add a WARN_ON(maxlen > > TASK_COMM_LEN).
Hmm, I thought current->comm is null terminated, isn't it? Anyway, if user can specify current->comm, he must be able to specify current->comm + TASK_COMM_LEN too by kprobe_events. Moreover, it can leak any data in kernel...
And also, maxlen is calculated by fetch_store_strlen, right before this has been called.
I rather concern the case that if we have shorter size of maxlen than current->comm. Would we better show "(fault)" or tail-cut name ? (of course this is very difficult to happen, since the length is already checked.)
Thank you,
> > -- Steve > > > > + else > > + ret = strncpy_from_user(dst, src, maxlen); > > if (ret >= 0) { > > if (ret == maxlen) > > dst[ret - 1] = '\0'; > > @@ -180,7 +183,12 @@ fetch_store_strlen(unsigned long addr) > > int len; > > void __user *vaddr = (void __force __user *) addr; > > > > - len = strnlen_user(vaddr, MAX_STRING_SIZE); > > + if (addr == (unsigned long)current->comm) { > > + len = strlen(current->comm); > > + if (len) > > + len++; > > + } else > > + len = strnlen_user(vaddr, MAX_STRING_SIZE); > > > > return (len > MAX_STRING_SIZE) ? 0 : len; > > } > > @@ -220,6 +228,9 @@ process_fetch_insn(struct fetch_insn *code, struct pt_regs *regs, void *dest, > > case FETCH_OP_IMM: > > val = code->immediate; > > break; > > + case FETCH_OP_COMM: > > + val = (unsigned long)current->comm; > > + break; > > case FETCH_OP_FOFFS: > > val = translate_user_vaddr(code->immediate); > > break; >
-- Masami Hiramatsu <mhiramat@kernel.org>
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