tracing: Fix possible NULL pointer dereferences

Currently set_ftrace_pid and set_graph_function files use seq_lseek
for their fops.  However seq_open() is called only for FMODE_READ in
the fops->open() so that if an user tries to seek one of those file
when she open it for writing, it sees NULL seq_file and then panic.

It can be easily reproduced with following command:

  $ cd /sys/kernel/debug/tracing
  $ echo 1234 | sudo tee -a set_ftrace_pid

In this example, GNU coreutils' tee opens the file with fopen(, "a")
and then the fopen() internally calls lseek().

Link: http://lkml.kernel.org/r/1365663302-2170-1-git-send-email-namhyung@kernel.org

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: stable@vger.kernel.org
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

2 files changed, 6 insertions, 6 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 926ebfb74936..affc35d829cc 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2697,7 +2697,7 @@ ftrace_notrace_open(struct inode *inode, struct file *file)
 }
 
 loff_t
-ftrace_regex_lseek(struct file *file, loff_t offset, int whence)
+ftrace_filter_lseek(struct file *file, loff_t offset, int whence)
 {
         loff_t ret;
 
@@ -3570,7 +3570,7 @@ static const struct file_operations ftrace_filter_fops = {
         .open = ftrace_filter_open,
         .read = seq_read,
         .write = ftrace_filter_write,
-        .llseek = ftrace_regex_lseek,
+        .llseek = ftrace_filter_lseek,
         .release = ftrace_regex_release,
 };
 
@@ -3578,7 +3578,7 @@ static const struct file_operations ftrace_notrace_fops = {
         .open = ftrace_notrace_open,
         .read = seq_read,
         .write = ftrace_notrace_write,
-        .llseek = ftrace_regex_lseek,
+        .llseek = ftrace_filter_lseek,
         .release = ftrace_regex_release,
 };
 
@@ -3783,8 +3783,8 @@ static const struct file_operations ftrace_graph_fops = {
         .open           = ftrace_graph_open,
         .read           = seq_read,
         .write          = ftrace_graph_write,
+        .llseek         = ftrace_filter_lseek,
         .release        = ftrace_graph_release,
-        .llseek         = seq_lseek,
 };
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 
@@ -4439,7 +4439,7 @@ static const struct file_operations ftrace_pid_fops = {
         .open           = ftrace_pid_open,
         .write          = ftrace_pid_write,
         .read           = seq_read,
-        .llseek         = seq_lseek,
+        .llseek         = ftrace_filter_lseek,
         .release        = ftrace_pid_release,
 };
 
diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index 42ca822fc701..83a8b5b7bd35 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -322,7 +322,7 @@ static const struct file_operations stack_trace_filter_fops = {
         .open = stack_trace_filter_open,
         .read = seq_read,
         .write = ftrace_filter_write,
-        .llseek = ftrace_regex_lseek,
+        .llseek = ftrace_filter_lseek,
         .release = ftrace_regex_release,
 };