Messages in this thread Patch in this message | | | Date | Thu, 17 Jan 2019 15:13:09 +0900 | From | Masami Hiramatsu <> | Subject | Re: uprobes: bug in comm/string output? |
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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.
For $comm support, use strncpy() 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 use strlen() instead of strlen_user() to measure the 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); + 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;
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