[38/75] tracing: Fix possible NULL pointer dereferences

[Ben Hutchings]

3.2.44-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Namhyung Kim <namhyung.kim@xxxxxxx>

commit 6a76f8c0ab19f215af2a3442870eeb5f0e81998d upstream.

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@xxxxxxxxxx

Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung.kim@xxxxxxx>
Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
[bwh: Backported to 3.2: ftrace_regex_lseek() is static]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2316,7 +2316,7 @@ ftrace_notrace_open(struct inode *inode,
 }
 
 static loff_t
-ftrace_regex_lseek(struct file *file, loff_t offset, int origin)
+ftrace_filter_lseek(struct file *file, loff_t offset, int origin)
 {
 	loff_t ret;
 
@@ -3134,7 +3134,7 @@ static const struct file_operations ftra
 	.open = ftrace_filter_open,
 	.read = seq_read,
 	.write = ftrace_filter_write,
-	.llseek = ftrace_regex_lseek,
+	.llseek = ftrace_filter_lseek,
 	.release = ftrace_regex_release,
 };
 
@@ -3142,7 +3142,7 @@ static const struct file_operations ftra
 	.open = ftrace_notrace_open,
 	.read = seq_read,
 	.write = ftrace_notrace_write,
-	.llseek = ftrace_regex_lseek,
+	.llseek = ftrace_filter_lseek,
 	.release = ftrace_regex_release,
 };
 
@@ -3350,8 +3350,8 @@ static const struct file_operations ftra
 	.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 */
 
@@ -3843,7 +3843,7 @@ static const struct file_operations ftra
 	.open		= ftrace_pid_open,
 	.write		= ftrace_pid_write,
 	.read		= seq_read,
-	.llseek		= seq_lseek,
+	.llseek		= ftrace_filter_lseek,
 	.release	= ftrace_pid_release,
 };
 

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/