Revert "bpf: replace snprintf with asprintf when dealing with long buffers"

This reverts commit c0325b0638.
It introduces a segfault in bpf_make_custom_path() when custom pinning is used.

This happens because asprintf allocates exactly the space needed to hold a
string in the buffer passed as its first argument, but if this buffer is later
used in strcat() or similar we have a buffer overrun.

As the aim of commit c0325b0638 is simply to fix a compiler warning, it
seems safe and reasonable to revert it.

Fixes: c0325b0638 ("bpf: replace snprintf with asprintf when dealing with long buffers")
Reported-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Andrea Claudi <aclaudi@redhat.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

lib/bpf.c

@@ -406,21 +406,13 @@ static int bpf_derive_elf_map_from_fdinfo(int fd, struct bpf_elf_map *map,
 					  struct bpf_map_ext *ext)
 {
 	unsigned int val, owner_type = 0, owner_jited = 0;
-	char *file = NULL;
+	char file[PATH_MAX], buff[4096];
-	char buff[4096];
 	FILE *fp;
-	int ret;
 
-	ret = asprintf(&file, "/proc/%d/fdinfo/%d", getpid(), fd);
+	snprintf(file, sizeof(file), "/proc/%d/fdinfo/%d", getpid(), fd);
-	if (ret < 0) {
-		fprintf(stderr, "asprintf failed: %s\n", strerror(errno));
-		free(file);
-		return ret;
-	}
 	memset(map, 0, sizeof(*map));
 
 	fp = fopen(file, "r");
-	free(file);
 	if (!fp) {
 		fprintf(stderr, "No procfs support?!\n");
 		return -EIO;
@@ -608,9 +600,8 @@ int bpf_trace_pipe(void)
 		0,
 	};
 	int fd_in, fd_out = STDERR_FILENO;
-	char *tpipe = NULL;
+	char tpipe[PATH_MAX];
 	const char *mnt;
-	int ret;
 
 	mnt = bpf_find_mntpt("tracefs", TRACEFS_MAGIC, tracefs_mnt,
 			     sizeof(tracefs_mnt), tracefs_known_mnts);
@@ -619,15 +610,9 @@ int bpf_trace_pipe(void)
 		return -1;
 	}
 
-	ret = asprintf(&tpipe, "%s/trace_pipe", mnt);
+	snprintf(tpipe, sizeof(tpipe), "%s/trace_pipe", mnt);
-	if (ret < 0) {
-		fprintf(stderr, "asprintf failed: %s\n", strerror(errno));
-		free(tpipe);
-		return ret;
-	}
 
 	fd_in = open(tpipe, O_RDONLY);
-	free(tpipe);
 	if (fd_in < 0)
 		return -1;
 
@@ -648,50 +633,37 @@ int bpf_trace_pipe(void)
 
 static int bpf_gen_global(const char *bpf_sub_dir)
 {
-	char *bpf_glo_dir = NULL;
+	char bpf_glo_dir[PATH_MAX];
 	int ret;
 
-	ret = asprintf(&bpf_glo_dir, "%s/%s/", bpf_sub_dir, BPF_DIR_GLOBALS);
+	snprintf(bpf_glo_dir, sizeof(bpf_glo_dir), "%s/%s/",
-	if (ret < 0) {
+		 bpf_sub_dir, BPF_DIR_GLOBALS);
-		fprintf(stderr, "asprintf failed: %s\n", strerror(errno));
-		goto out;
-	}
 
 	ret = mkdir(bpf_glo_dir, S_IRWXU);
 	if (ret && errno != EEXIST) {
 		fprintf(stderr, "mkdir %s failed: %s\n", bpf_glo_dir,
 			strerror(errno));
-		goto out;
+		return ret;
 	}
 
-	ret = 0;
+	return 0;
-out:
-	free(bpf_glo_dir);
-	return ret;
 }
 
 static int bpf_gen_master(const char *base, const char *name)
 {
-	char *bpf_sub_dir = NULL;
+	char bpf_sub_dir[PATH_MAX + NAME_MAX + 1];
 	int ret;
 
-	ret = asprintf(&bpf_sub_dir, "%s%s/", base, name);
+	snprintf(bpf_sub_dir, sizeof(bpf_sub_dir), "%s%s/", base, name);
-	if (ret < 0) {
-		fprintf(stderr, "asprintf failed: %s\n", strerror(errno));
-		goto out;
-	}
 
 	ret = mkdir(bpf_sub_dir, S_IRWXU);
 	if (ret && errno != EEXIST) {
 		fprintf(stderr, "mkdir %s failed: %s\n", bpf_sub_dir,
 			strerror(errno));
-		goto out;
+		return ret;
 	}
 
-	ret = bpf_gen_global(bpf_sub_dir);
+	return bpf_gen_global(bpf_sub_dir);
-out:
-	free(bpf_sub_dir);
-	return ret;
 }
 
 static int bpf_slave_via_bind_mnt(const char *full_name,
@@ -720,22 +692,13 @@ static int bpf_slave_via_bind_mnt(const char *full_name,
 static int bpf_gen_slave(const char *base, const char *name,
 			 const char *link)
 {
-	char *bpf_lnk_dir = NULL;
+	char bpf_lnk_dir[PATH_MAX + NAME_MAX + 1];
-	char *bpf_sub_dir = NULL;
+	char bpf_sub_dir[PATH_MAX + NAME_MAX];
 	struct stat sb = {};
 	int ret;
 
-	ret = asprintf(&bpf_lnk_dir, "%s%s/", base, link);
+	snprintf(bpf_lnk_dir, sizeof(bpf_lnk_dir), "%s%s/", base, link);
-	if (ret < 0) {
+	snprintf(bpf_sub_dir, sizeof(bpf_sub_dir), "%s%s",  base, name);
-		fprintf(stderr, "asprintf failed: %s\n", strerror(errno));
-		goto out;
-	}
-
-	ret = asprintf(&bpf_sub_dir, "%s%s",  base, name);
-	if (ret < 0) {
-		fprintf(stderr, "asprintf failed: %s\n", strerror(errno));
-		goto out;
-	}
 
 	ret = symlink(bpf_lnk_dir, bpf_sub_dir);
 	if (ret) {
@@ -743,30 +706,25 @@ static int bpf_gen_slave(const char *base, const char *name,
 			if (errno != EPERM) {
 				fprintf(stderr, "symlink %s failed: %s\n",
 					bpf_sub_dir, strerror(errno));
-				goto out;
+				return ret;
 			}
 
-			ret = bpf_slave_via_bind_mnt(bpf_sub_dir, bpf_lnk_dir);
+			return bpf_slave_via_bind_mnt(bpf_sub_dir,
-			goto out;
+						      bpf_lnk_dir);
 		}
 
 		ret = lstat(bpf_sub_dir, &sb);
 		if (ret) {
 			fprintf(stderr, "lstat %s failed: %s\n",
 				bpf_sub_dir, strerror(errno));
-			goto out;
+			return ret;
 		}
 
-		if ((sb.st_mode & S_IFMT) != S_IFLNK) {
+		if ((sb.st_mode & S_IFMT) != S_IFLNK)
-			ret = bpf_gen_global(bpf_sub_dir);
+			return bpf_gen_global(bpf_sub_dir);
-			goto out;
-		}
 	}
 
-out:
+	return 0;
-	free(bpf_lnk_dir);
-	free(bpf_sub_dir);
-	return ret;
 }
 
 static int bpf_gen_hierarchy(const char *base)
@@ -784,7 +742,7 @@ static int bpf_gen_hierarchy(const char *base)
 static const char *bpf_get_work_dir(enum bpf_prog_type type)
 {
 	static char bpf_tmp[PATH_MAX] = BPF_DIR_MNT;
-	static char *bpf_wrk_dir;
+	static char bpf_wrk_dir[PATH_MAX];
 	static const char *mnt;
 	static bool bpf_mnt_cached;
 	const char *mnt_env = getenv(BPF_ENV_MNT);
@@ -823,12 +781,7 @@ static const char *bpf_get_work_dir(enum bpf_prog_type type)
 		}
 	}
 
-	ret = asprintf(&bpf_wrk_dir, "%s/", mnt);
+	snprintf(bpf_wrk_dir, sizeof(bpf_wrk_dir), "%s/", mnt);
-	if (ret < 0) {
-		fprintf(stderr, "asprintf failed: %s\n", strerror(errno));
-		free(bpf_wrk_dir);
-		goto out;
-	}
 
 	ret = bpf_gen_hierarchy(bpf_wrk_dir);
 	if (ret) {
@@ -1485,48 +1438,31 @@ static int bpf_probe_pinned(const char *name, const struct bpf_elf_ctx *ctx,
 
 static int bpf_make_obj_path(const struct bpf_elf_ctx *ctx)
 {
-	char *tmp = NULL;
+	char tmp[PATH_MAX];
 	int ret;
 
-	ret = asprintf(&tmp, "%s/%s", bpf_get_work_dir(ctx->type), ctx->obj_uid);
+	snprintf(tmp, sizeof(tmp), "%s/%s", bpf_get_work_dir(ctx->type),
-	if (ret < 0) {
+		 ctx->obj_uid);
-		fprintf(stderr, "asprintf failed: %s\n", strerror(errno));
-		goto out;
-	}
 
 	ret = mkdir(tmp, S_IRWXU);
 	if (ret && errno != EEXIST) {
 		fprintf(stderr, "mkdir %s failed: %s\n", tmp, strerror(errno));
-		goto out;
+		return ret;
 	}
 
-	ret = 0;
+	return 0;
-out:
-	free(tmp);
-	return ret;
 }
 
 static int bpf_make_custom_path(const struct bpf_elf_ctx *ctx,
 				const char *todo)
 {
-	char *tmp = NULL;
+	char tmp[PATH_MAX], rem[PATH_MAX], *sub;
-	char *rem = NULL;
-	char *sub;
 	int ret;
 
-	ret = asprintf(&tmp, "%s/../", bpf_get_work_dir(ctx->type));
+	snprintf(tmp, sizeof(tmp), "%s/../", bpf_get_work_dir(ctx->type));
-	if (ret < 0) {
+	snprintf(rem, sizeof(rem), "%s/", todo);
-		fprintf(stderr, "asprintf failed: %s\n", strerror(errno));
-		goto out;
-	}
-
-	ret = asprintf(&rem, "%s/", todo);
-	if (ret < 0) {
-		fprintf(stderr, "asprintf failed: %s\n", strerror(errno));
-		goto out;
-	}
-
 	sub = strtok(rem, "/");
+
 	while (sub) {
 		if (strlen(tmp) + strlen(sub) + 2 > PATH_MAX)
 			return -EINVAL;
@@ -1538,17 +1474,13 @@ static int bpf_make_custom_path(const struct bpf_elf_ctx *ctx,
 		if (ret && errno != EEXIST) {
 			fprintf(stderr, "mkdir %s failed: %s\n", tmp,
 				strerror(errno));
-			goto out;
+			return ret;
 		}
 
 		sub = strtok(NULL, "/");
 	}
 
-	ret = 0;
+	return 0;
-out:
-	free(rem);
-	free(tmp);
-	return ret;
 }
 
 static int bpf_place_pinned(int fd, const char *name,
@@ -2655,23 +2587,14 @@ struct bpf_jited_aux {
 
 static int bpf_derive_prog_from_fdinfo(int fd, struct bpf_prog_data *prog)
 {
-	char *file = NULL;
+	char file[PATH_MAX], buff[4096];
-	char buff[4096];
 	unsigned int val;
 	FILE *fp;
-	int ret;
-
-	ret = asprintf(&file, "/proc/%d/fdinfo/%d", getpid(), fd);
-	if (ret < 0) {
-		fprintf(stderr, "asprintf failed: %s\n", strerror(errno));
-		free(file);
-		return ret;
-	}
 
+	snprintf(file, sizeof(file), "/proc/%d/fdinfo/%d", getpid(), fd);
 	memset(prog, 0, sizeof(*prog));
 
 	fp = fopen(file, "r");
-	free(file);
 	if (!fp) {
 		fprintf(stderr, "No procfs support?!\n");
 		return -EIO;