lib/fs: fix memory leak in get_task_name()

asprintf() allocates memory which is not freed on the error path of
get_task_name(), thus potentially leading to memory leaks.
%m specifier on fscanf allocates memory, too, which needs to be freed by
the caller.

This reworks get_task_name() to avoid memory allocation.
- Pass a buffer and its length to the function, similarly to what
  get_command_name() does, thus avoiding to allocate memory for
  the string to be returned;
- Use snprintf() instead of asprintf();
- Use fgets() instead of fscanf() to limit string length.

Fixes: 81bfd01a4c9e ("lib: move get_task_name() from rdma")
Signed-off-by: Andrea Claudi <aclaudi@redhat.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

11 files changed, 57 insertions, 39 deletions

diff --git a/include/utils.h b/include/utils.h
index b6c468e9c..b0e0967cb 100644
--- a/include/utils.h
+++ b/include/utils.h
@@ -307,7 +307,7 @@ char *find_cgroup2_mount(bool do_mount);
 __u64 get_cgroup2_id(const char *path);
 char *get_cgroup2_path(__u64 id, bool full);
 int get_command_name(const char *pid, char *comm, size_t len);
-char *get_task_name(pid_t pid);
+int get_task_name(pid_t pid, char *name, size_t len);
 
 int get_rtnl_link_stats_rta(struct rtnl_link_stats64 *stats64,
 			    struct rtattr *tb[]);
diff --git a/ip/iptuntap.c b/ip/iptuntap.c
index 385d2bd80..8e4e09bff 100644
--- a/ip/iptuntap.c
+++ b/ip/iptuntap.c
@@ -321,14 +321,16 @@ static void show_processes(const char *name)
 			} else if (err == 2 &&
 				   !strcmp("iff", key) &&
 				   !strcmp(name, value)) {
-				char *pname = get_task_name(pid);
+				SPRINT_BUF(pname);
 
-				print_string(PRINT_ANY, "name",
-					     "%s", pname ? : "<NULL>");
+				if (get_task_name(pid, pname, sizeof(pname)))
+					print_string(PRINT_ANY, "name",
+						     "%s", "<NULL>");
+				else
+					print_string(PRINT_ANY, "name",
+						     "%s", pname);
 
-				print_uint(PRINT_ANY, "pid",
-					   "(%d)", pid);
-				free(pname);
+				print_uint(PRINT_ANY, "pid", "(%d)", pid);
 			}
 
 			free(key);
diff --git a/lib/fs.c b/lib/fs.c
index f6f5f8a0b..3752931cf 100644
--- a/lib/fs.c
+++ b/lib/fs.c
@@ -342,25 +342,28 @@ int get_command_name(const char *pid, char *comm, size_t len)
 	return 0;
 }
 
-char *get_task_name(pid_t pid)
+int get_task_name(pid_t pid, char *name, size_t len)
 {
-	char *comm;
+	char path[PATH_MAX];
 	FILE *f;
 
 	if (!pid)
-		return NULL;
+		return -1;
 
-	if (asprintf(&comm, "/proc/%d/comm", pid) < 0)
-		return NULL;
+	if (snprintf(path, sizeof(path), "/proc/%d/comm", pid) >= sizeof(path))
+		return -1;
 
-	f = fopen(comm, "r");
+	f = fopen(path, "r");
 	if (!f)
-		return NULL;
+		return -1;
 
-	if (fscanf(f, "%ms\n", &comm) != 1)
-		comm = NULL;
+	if (!fgets(name, len, f))
+		return -1;
+
+	/* comm ends in \n, get rid of it */
+	name[strcspn(name, "\n")] = '\0';
 
 	fclose(f);
 
-	return comm;
+	return 0;
 }
diff --git a/rdma/res-cmid.c b/rdma/res-cmid.c
index fd57dbb79..b532d7f43 100644
--- a/rdma/res-cmid.c
+++ b/rdma/res-cmid.c
@@ -159,8 +159,11 @@ static int res_cm_id_line(struct rd *rd, const char *name, int idx,
 		goto out;
 
 	if (nla_line[RDMA_NLDEV_ATTR_RES_PID]) {
+		SPRINT_BUF(b);
+
 		pid = mnl_attr_get_u32(nla_line[RDMA_NLDEV_ATTR_RES_PID]);
-		comm = get_task_name(pid);
+		if (!get_task_name(pid, b, sizeof(b)))
+			comm = b;
 	}
 
 	if (rd_is_filtered_attr(rd, "pid", pid,
@@ -199,8 +202,7 @@ static int res_cm_id_line(struct rd *rd, const char *name, int idx,
 	print_driver_table(rd, nla_line[RDMA_NLDEV_ATTR_DRIVER]);
 	newline(rd);
 
-out:	if (nla_line[RDMA_NLDEV_ATTR_RES_PID])
-		free(comm);
+out:
 	return MNL_CB_OK;
 }
 
diff --git a/rdma/res-cq.c b/rdma/res-cq.c
index 818e1d0c2..a4625afc3 100644
--- a/rdma/res-cq.c
+++ b/rdma/res-cq.c
@@ -84,8 +84,11 @@ static int res_cq_line(struct rd *rd, const char *name, int idx,
 		goto out;
 
 	if (nla_line[RDMA_NLDEV_ATTR_RES_PID]) {
+		SPRINT_BUF(b);
+
 		pid = mnl_attr_get_u32(nla_line[RDMA_NLDEV_ATTR_RES_PID]);
-		comm = get_task_name(pid);
+		if (!get_task_name(pid, b, sizeof(b)))
+			comm = b;
 	}
 
 	if (rd_is_filtered_attr(rd, "pid", pid,
@@ -123,8 +126,7 @@ static int res_cq_line(struct rd *rd, const char *name, int idx,
 	print_driver_table(rd, nla_line[RDMA_NLDEV_ATTR_DRIVER]);
 	newline(rd);
 
-out:	if (nla_line[RDMA_NLDEV_ATTR_RES_PID])
-		free(comm);
+out:
 	return MNL_CB_OK;
 }
 
diff --git a/rdma/res-ctx.c b/rdma/res-ctx.c
index ea5faf182..79ecbf674 100644
--- a/rdma/res-ctx.c
+++ b/rdma/res-ctx.c
@@ -18,8 +18,11 @@ static int res_ctx_line(struct rd *rd, const char *name, int idx,
 		return MNL_CB_ERROR;
 
 	if (nla_line[RDMA_NLDEV_ATTR_RES_PID]) {
+		SPRINT_BUF(b);
+
 		pid = mnl_attr_get_u32(nla_line[RDMA_NLDEV_ATTR_RES_PID]);
-		comm = get_task_name(pid);
+		if (!get_task_name(pid, b, sizeof(b)))
+			comm = b;
 	}
 
 	if (rd_is_filtered_attr(rd, "pid", pid,
@@ -48,8 +51,6 @@ static int res_ctx_line(struct rd *rd, const char *name, int idx,
 	newline(rd);
 
 out:
-	if (nla_line[RDMA_NLDEV_ATTR_RES_PID])
-		free(comm);
 	return MNL_CB_OK;
 }
 
diff --git a/rdma/res-mr.c b/rdma/res-mr.c
index 25eaa0562..7153a6fea 100644
--- a/rdma/res-mr.c
+++ b/rdma/res-mr.c
@@ -47,8 +47,11 @@ static int res_mr_line(struct rd *rd, const char *name, int idx,
 		goto out;
 
 	if (nla_line[RDMA_NLDEV_ATTR_RES_PID]) {
+		SPRINT_BUF(b);
+
 		pid = mnl_attr_get_u32(nla_line[RDMA_NLDEV_ATTR_RES_PID]);
-		comm = get_task_name(pid);
+		if (!get_task_name(pid, b, sizeof(b)))
+			comm = b;
 	}
 
 	if (rd_is_filtered_attr(rd, "pid", pid,
@@ -87,8 +90,6 @@ static int res_mr_line(struct rd *rd, const char *name, int idx,
 	newline(rd);
 
 out:
-	if (nla_line[RDMA_NLDEV_ATTR_RES_PID])
-		free(comm);
 	return MNL_CB_OK;
 }
 
diff --git a/rdma/res-pd.c b/rdma/res-pd.c
index 2932eb986..09c1040c5 100644
--- a/rdma/res-pd.c
+++ b/rdma/res-pd.c
@@ -34,8 +34,11 @@ static int res_pd_line(struct rd *rd, const char *name, int idx,
 			nla_line[RDMA_NLDEV_ATTR_RES_UNSAFE_GLOBAL_RKEY]);
 
 	if (nla_line[RDMA_NLDEV_ATTR_RES_PID]) {
+		SPRINT_BUF(b);
+
 		pid = mnl_attr_get_u32(nla_line[RDMA_NLDEV_ATTR_RES_PID]);
-		comm = get_task_name(pid);
+		if (!get_task_name(pid, b, sizeof(b)))
+			comm = b;
 	}
 
 	if (rd_is_filtered_attr(rd, "pid", pid,
@@ -76,8 +79,7 @@ static int res_pd_line(struct rd *rd, const char *name, int idx,
 	print_driver_table(rd, nla_line[RDMA_NLDEV_ATTR_DRIVER]);
 	newline(rd);
 
-out:	if (nla_line[RDMA_NLDEV_ATTR_RES_PID])
-		free(comm);
+out:
 	return MNL_CB_OK;
 }
 
diff --git a/rdma/res-qp.c b/rdma/res-qp.c
index 9218804a8..151accb9d 100644
--- a/rdma/res-qp.c
+++ b/rdma/res-qp.c
@@ -146,8 +146,11 @@ static int res_qp_line(struct rd *rd, const char *name, int idx,
 		goto out;
 
 	if (nla_line[RDMA_NLDEV_ATTR_RES_PID]) {
+		SPRINT_BUF(b);
+
 		pid = mnl_attr_get_u32(nla_line[RDMA_NLDEV_ATTR_RES_PID]);
-		comm = get_task_name(pid);
+		if (!get_task_name(pid, b, sizeof(b)))
+			comm = b;
 	}
 
 	if (rd_is_filtered_attr(rd, "pid", pid,
@@ -179,8 +182,6 @@ static int res_qp_line(struct rd *rd, const char *name, int idx,
 	print_driver_table(rd, nla_line[RDMA_NLDEV_ATTR_DRIVER]);
 	newline(rd);
 out:
-	if (nla_line[RDMA_NLDEV_ATTR_RES_PID])
-		free(comm);
 	return MNL_CB_OK;
 }
 
diff --git a/rdma/res-srq.c b/rdma/res-srq.c
index c6df454a2..f3a652d82 100644
--- a/rdma/res-srq.c
+++ b/rdma/res-srq.c
@@ -174,8 +174,11 @@ static int res_srq_line(struct rd *rd, const char *name, int idx,
 		return MNL_CB_ERROR;
 
 	if (nla_line[RDMA_NLDEV_ATTR_RES_PID]) {
+		SPRINT_BUF(b);
+
 		pid = mnl_attr_get_u32(nla_line[RDMA_NLDEV_ATTR_RES_PID]);
-		comm = get_task_name(pid);
+		if (!get_task_name(pid, b, sizeof(b)))
+			comm = b;
 	}
 	if (rd_is_filtered_attr(rd, "pid", pid,
 				nla_line[RDMA_NLDEV_ATTR_RES_PID]))
@@ -228,8 +231,6 @@ static int res_srq_line(struct rd *rd, const char *name, int idx,
 	newline(rd);
 
 out:
-	if (nla_line[RDMA_NLDEV_ATTR_RES_PID])
-		free(comm);
 	return MNL_CB_OK;
 }
 
diff --git a/rdma/stat.c b/rdma/stat.c
index c7da29225..ab0629155 100644
--- a/rdma/stat.c
+++ b/rdma/stat.c
@@ -248,8 +248,11 @@ static int res_counter_line(struct rd *rd, const char *name, int index,
 		return MNL_CB_OK;
 
 	if (nla_line[RDMA_NLDEV_ATTR_RES_PID]) {
+		SPRINT_BUF(b);
+
 		pid = mnl_attr_get_u32(nla_line[RDMA_NLDEV_ATTR_RES_PID]);
-		comm = get_task_name(pid);
+		if (!get_task_name(pid, b, sizeof(b)))
+			comm = b;
 	}
 	if (rd_is_filtered_attr(rd, "pid", pid,
 				nla_line[RDMA_NLDEV_ATTR_RES_PID]))