cmds: static variable used stack after return #1924

yskelg · 2024-05-11T16:24:07Z

ASAN detect stack after return on this scenario.

$ uftrace record --agent --trace=off ./valkey-server

$ uftrace --pid `pidof valkey-server` --trace=on
$ uftrace --pid `pidof valkey-server` --trace=off

This patch fix #1915 static tmp_dirname variable not pointed command_live()'s char template array stack variable.

yskelg · 2024-05-11T16:30:27Z

cmds/live.c

 static void cleanup_tempdir(void)
 {
-	if (!tmp_dirname)
-		return;
-
 	remove_directory(tmp_dirname);


I think wrong dirname would be covered with opendir() cheking.

But let's check if tmp_dirname has a valid string first.

I think it's ok to check the first byte only.

if (tmp_dirname[0] == '\0') return;

I agree, Done!

namhyung · 2024-05-12T04:35:25Z

cmds/live.c

+#define TMP_DIR_NAME_SIZE 32
+
+static char tmp_dirname[TMP_DIR_NAME_SIZE] = {
+	'\0',


I think you can initialize it with LIVE_NAME below.

Done @namhyung 👍

namhyung · 2024-05-12T04:35:51Z

cmds/live.c

 static void cleanup_tempdir(void)
 {
-	if (!tmp_dirname)
-		return;
-
 	remove_directory(tmp_dirname);


But let's check if tmp_dirname has a valid string first.

namhyung · 2024-05-12T04:36:10Z

cmds/live.c

 	remove_directory(tmp_dirname);
-	tmp_dirname = NULL;
+	memset(tmp_dirname, 0, sizeof(char) * TMP_DIR_NAME_SIZE);


You can just use sizeof(tmp_dirname);

Thank for the idea!

namhyung · 2024-05-12T04:36:28Z

cmds/live.c

@@ -416,15 +417,14 @@ static int forward_options(struct uftrace_opts *opts)
 int command_live(int argc, char *argv[], struct uftrace_opts *opts)
 {
 #define LIVE_NAME "uftrace-live-XXXXXX"
-	char template[32] = "/tmp/" LIVE_NAME;
+	char template[TMP_DIR_NAME_SIZE] = "/tmp/" LIVE_NAME;


Now we can remove the template.

namhyung · 2024-05-12T04:40:08Z

cmds/live.c


+		unlink(template);
+
+		snprintf(tmp_dirname, strlen(template), "%s", template);


You should use sizeof(tmp_dirname) instead of strlen(template), otherwise it might not set the last NUL byte.

Thank you @namhyung. good advice! 👍

paranlee · 2024-05-15T14:51:53Z

cmds/live.c

 			if (errno != EPERM && errno != ENOENT)
-				pr_err("cannot access to /tmp");
+				pr_err("cannot access to " TMP_LIVE_NAME);


I think non-sense situation that someone makes directory or symbolic link named /tmp/uftrace-live-XXXXXX.

mkstemp would replace "XXXXXX" to a random string. You need to print the actual string in tmp_dirname.

paranlee · 2024-05-15T14:51:58Z

cmds/live.c

+#define LIVE_NAME "uftrace-live-XXXXXX"
+#define TMP_LIVE_NAME "/tmp/" LIVE_NAME


String comparison makes macro going to top of the code.

namhyung · 2024-05-18T00:45:31Z

cmds/live.c

 static void cleanup_tempdir(void)
 {
-	if (!tmp_dirname)
+	if (strncmp(TMP_LIVE_NAME, tmp_dirname, strlen(TMP_LIVE_NAME)) != 0 ||
+	    strncmp(LIVE_NAME, tmp_dirname, strlen(LIVE_NAME)) != 0) {


This condition is always true. You need to check if it has non-zero contents.

Done @namhyung 👍

namhyung · 2024-05-18T00:46:47Z

cmds/live.c

 			if (errno != EPERM && errno != ENOENT)
-				pr_err("cannot access to /tmp");
+				pr_err("cannot access to " TMP_LIVE_NAME);


mkstemp would replace "XXXXXX" to a random string. You need to print the actual string in tmp_dirname.

namhyung · 2024-05-18T00:47:01Z

cmds/live.c


 			if (fd < 0)
-				pr_err("cannot create temp name");
-			tmp_dirname = template;
+				pr_err("cannot create " LIVE_NAME);


Thank you @namhyung, I understand the mkstemp would replace "XXXXXX". Done!

namhyung

Also, this change is specific to live command. So the commit subject should start with "live:" instead of generic "cmds:".

ASAN detect stack after return on this scenario. $ uftrace record --agent --trace=off ./valkey-server $ uftrace --pid `pidof valkey-server` --trace=on $ uftrace --pid `pidof valkey-server` --trace=off This patch fix static tmp_dirname variable not pointed command_live()'s char template array stack variable. Signed-off-by: Yunseong Kim <yskelg@gmail.com>

namhyung

LGTM

yskelg force-pushed the update-ended-stack-pointer branch from 1d534cc to 4e913bf Compare May 11, 2024 16:27

yskelg commented May 11, 2024

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yskelg force-pushed the update-ended-stack-pointer branch from 4e913bf to f5f513c Compare May 11, 2024 16:33

namhyung reviewed May 12, 2024

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yskelg force-pushed the update-ended-stack-pointer branch 3 times, most recently from e3a4078 to 9afc188 Compare May 15, 2024 14:46

paranlee reviewed May 15, 2024

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yskelg closed this May 15, 2024

yskelg force-pushed the update-ended-stack-pointer branch from 9afc188 to d79deba Compare May 15, 2024 14:56

yskelg reopened this May 15, 2024

namhyung reviewed May 18, 2024

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yskelg force-pushed the update-ended-stack-pointer branch from 3532ea8 to 5218f60 Compare May 18, 2024 05:34

namhyung reviewed May 18, 2024

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yskelg force-pushed the update-ended-stack-pointer branch from 5218f60 to 91e10b0 Compare May 18, 2024 15:50

yskelg force-pushed the update-ended-stack-pointer branch from 91e10b0 to ea31643 Compare May 18, 2024 15:54

namhyung approved these changes May 19, 2024

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namhyung merged commit a4963f8 into namhyung:master May 21, 2024
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cmds: static variable used stack after return #1924

cmds: static variable used stack after return #1924

yskelg commented May 11, 2024 •

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		unlink(template);

		snprintf(tmp_dirname, strlen(template), "%s", template);

		#define LIVE_NAME "uftrace-live-XXXXXX"
		#define TMP_LIVE_NAME "/tmp/" LIVE_NAME

cmds: static variable used stack after return #1924

cmds: static variable used stack after return #1924

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yskelg commented May 11, 2024 • edited Loading

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yskelg commented May 11, 2024 •

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