[PATCH v2 1/3] tracing: uprobes: Re-enable $comm support for uprobe events

[Masami Hiramatsu]

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 <mhira...@kernel.org>
Reported-by: Andreas Ziegler <andreas.zieg...@fau.de>
Acked-by: Andreas Ziegler <andreas.zieg...@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);
+       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;