In Documentation/trace/kprobetrace.txt, it says

 @SYM[+|-offs] : Fetch memory at SYM +|- offs (SYM should be a data symbol)

However, the parser doesn't parse minus offset correctly, since
commit 2fba0c8867af ("tracing/kprobes: Fix probe offset to be
unsigned") drops minus ("-") offset support for kprobe probe
address usage.

This fixes the traceprobe_split_symbol_offset() to parse minus
offset again with checking the offset range, and add a minus
offset check in kprobe probe address usage.

Fixes: 2fba0c8867af ("tracing/kprobes: Fix probe offset to be unsigned")
Signed-off-by: Masami Hiramatsu <mhira...@kernel.org>
---
 Changes in v3:
  - Use kstrtol instead of kstrtoul. (Thanks Namhyung!)
---
 kernel/trace/trace_kprobe.c |    4 ++--
 kernel/trace/trace_probe.c  |    8 +++-----
 kernel/trace/trace_probe.h  |    2 +-
 3 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 5ce9b8cf7be3..b5b1d8aa47d6 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -667,7 +667,7 @@ static int create_trace_kprobe(int argc, char **argv)
        char *symbol = NULL, *event = NULL, *group = NULL;
        int maxactive = 0;
        char *arg;
-       unsigned long offset = 0;
+       long offset = 0;
        void *addr = NULL;
        char buf[MAX_EVENT_NAME_LEN];
 
@@ -755,7 +755,7 @@ static int create_trace_kprobe(int argc, char **argv)
                symbol = argv[1];
                /* TODO: support .init module functions */
                ret = traceprobe_split_symbol_offset(symbol, &offset);
-               if (ret) {
+               if (ret || offset < 0) {
                        pr_info("Failed to parse either an address or a 
symbol.\n");
                        return ret;
                }
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index d59357308677..d3d1ee820336 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -320,7 +320,7 @@ static fetch_func_t get_fetch_size_function(const struct 
fetch_type *type,
 }
 
 /* Split symbol and offset. */
-int traceprobe_split_symbol_offset(char *symbol, unsigned long *offset)
+int traceprobe_split_symbol_offset(char *symbol, long *offset)
 {
        char *tmp;
        int ret;
@@ -328,13 +328,11 @@ int traceprobe_split_symbol_offset(char *symbol, unsigned 
long *offset)
        if (!offset)
                return -EINVAL;
 
-       tmp = strchr(symbol, '+');
+       tmp = strpbrk(symbol, "+-");
        if (tmp) {
-               /* skip sign because kstrtoul doesn't accept '+' */
-               ret = kstrtoul(tmp + 1, 0, offset);
+               ret = kstrtol(tmp + 1, 0, offset);
                if (ret)
                        return ret;
-
                *tmp = '\0';
        } else
                *offset = 0;
diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index 0745f895f780..75daff22ccea 100644
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -365,7 +365,7 @@ extern int traceprobe_conflict_field_name(const char *name,
 extern void traceprobe_update_arg(struct probe_arg *arg);
 extern void traceprobe_free_probe_arg(struct probe_arg *arg);
 
-extern int traceprobe_split_symbol_offset(char *symbol, unsigned long *offset);
+extern int traceprobe_split_symbol_offset(char *symbol, long *offset);
 
 /* Sum up total data length for dynamic arraies (strings) */
 static nokprobe_inline int

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