Messages in this thread | | | Date | Thu, 17 Jan 2019 14:47:46 +0100 | From | Greg Kroah-Hartman <> | Subject | Re: uprobes: bug in comm/string output? |
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On Thu, Jan 17, 2019 at 02:44:41PM +0100, Andreas Ziegler wrote: > Hi, > > On 1/17/19 10:47 AM, Masami Hiramatsu wrote: > > On Thu, 17 Jan 2019 09:08:41 +0100 > > Andreas Ziegler <andreas.ziegler@fau.de> wrote: > > > > > On 17.01.19 09:00, Masami Hiramatsu wrote: > > > > On Thu, 17 Jan 2019 15:13:09 +0900 > > > > Masami Hiramatsu <mhiramat@kernel.org> wrote: > > > > > > > > > On Wed, 16 Jan 2019 11:16:07 +0100 > > > > > Andreas Ziegler <andreas.ziegler@fau.de> wrote: > > > > > > > > > > > > > > > > > I went into this a bit deeper today, and right now it is simply failing > > > > > > to parse the code because there is no FETCH_OP_COMM case in > > > > > > process_fetch_insn() for uprobes so that will return -EILSEQ, leading to > > > > > > a make_data_loc(0, ...) in store_trace_args(). If we just add > > > > > > FETCH_OP_COMM and let val point to current->comm (that's what > > > > > > trace_kprobe.c does), we get an -EFAULT return value from > > > > > > fetch_store_string because strncpy_from_user() checks if the argument is > > > > > > in user space. > > > > > > > > > > Correct. I missed to add OP_COMM support. And uprobe's fetch_store_string > > > > > is only for user space strings. > > > > > > > > > > > So I think we might need a special case for that, something like > > > > > > FETCH_OP_ST_COMM_STRING which is only used for FETCH_OP_COMM and copies > > > > > > current->comm over to the dynamic area. The implementation could be > > > > > > similar to the old fetch_comm_string implementation before your rewrite. > > > > > > > > > > Hmm, instead, I would like to add current->comm checker and only allows > > > > > to copy that. That would be simpler and enough. > > > > > > > > > > Could you test below patch? > > > > > > > > > > > > > > > tracing: uprobes: Re-enable $comm support for uprobe events > > > > > > > > > > From: Masami Hiramatsu <mhiramat@kernel.org> > > > > > > > > > > Since commit 533059281ee5 ("tracing: probeevent: Introduce new > > > > > argument fetching code") dropped the $comm support from uprobe > > > > > events, this re-enable it. > > > > > > this should read 're-enables'. > > > > > > > > > > > > > For $comm support, use strncpy() instead of strncpy_from_user() > > > ^ > > > we're using strlcpy(), not strncpy(). > > > > > > > > to copy current task's comm. Because it is in the kernel space, > > > > > strncpy_from_user() always fails to copy the comm. > > > > > This also use strlen() instead of strlen_user() to measure the > > > ^ ^ > > > 'uses', and the function should be 'strnlen_user()'. > > > > > > > > length of the comm. > > > > > > > > > > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> > > > > > Reported-by: Andreas Ziegler <andreas.ziegler@fau.de> > > > > > --- > > > > > kernel/trace/trace_uprobe.c | 13 +++++++++++-- > > > > > 1 file changed, 11 insertions(+), 2 deletions(-) > > > > > > > > > > diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c > > > > > index e335576b9411..97d134e83e0f 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); > > > > > + else > > > > > + ret = strncpy_from_user(dst, src, maxlen); > > > > > if (ret >= 0) { > > > > > if (ret == maxlen) > > > > > dst[ret - 1] = '\0'; > > > > > @@ -173,7 +176,10 @@ 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); > > > > > > > > To balance with the strnlen_user, we must increse the len in this block. > > > > (strlen doesn't count the final '\0', but strnlen_user counts it) > > > > > > > > > > yes, we need to add a '+ 1' here. > > > > > > With the typos and this one fixed, this is > > > > > > Acked-by: Andreas Ziegler <andreas.ziegler@fau.de> > > > > Thank you for fixing typo and Ack :) > > > > Thanks you, > > > > > > > > > Thank you, > > > > > > > > > + else > > > > > + len = strnlen_user(vaddr, MAX_STRING_SIZE); > > > > > return (len > MAX_STRING_SIZE) ? 0 : len; > > > > > } > > > > > @@ -213,6 +219,9 @@ 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; > > > > > > > > > > > > > > > > as the original commit breaking $comm support was merged for v4.20 (which is > a stable kernel) and the wrong behaviour with multiple strings exists in all > longterm/stable releases (tested back to v4.4), do you think this should be > going into a stable release once it's merged? > > I added Greg as he might know the answer to that.
Sounds like it would be a patch to be backported to the stable kernels to me.
greg k-h
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