[iproute2-next] bpf: replace snprintf with asprintf when dealing with long buffers
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Message ID d2631870837a01f1488bf0bd547bb126f24de6b9.1568043463.git.aclaudi@redhat.com
State Changes Requested
Delegated to: David Ahern
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Series
  • [iproute2-next] bpf: replace snprintf with asprintf when dealing with long buffers
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Commit Message

Andrea Claudi Sept. 9, 2019, 4:05 p.m. UTC
This reduces stack usage, as asprintf allocates memory on the heap.

This indirectly fixes a snprintf truncation warning (from gcc v9.2.1):

bpf.c: In function ‘bpf_get_work_dir’:
bpf.c:784:49: warning: ‘snprintf’ output may be truncated before the last format character [-Wformat-truncation=]
  784 |  snprintf(bpf_wrk_dir, sizeof(bpf_wrk_dir), "%s/", mnt);
      |                                                 ^
bpf.c:784:2: note: ‘snprintf’ output between 2 and 4097 bytes into a destination of size 4096
  784 |  snprintf(bpf_wrk_dir, sizeof(bpf_wrk_dir), "%s/", mnt);
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fixes: e42256699cac ("bpf: make tc's bpf loader generic and move into lib")
Signed-off-by: Andrea Claudi <aclaudi@redhat.com>
---
 lib/bpf.c | 95 +++++++++++++++++++++++++++++++++----------------------
 1 file changed, 57 insertions(+), 38 deletions(-)

Comments

David Ahern Sept. 15, 2019, 5:45 p.m. UTC | #1
On 9/9/19 10:05 AM, Andrea Claudi wrote:
> This reduces stack usage, as asprintf allocates memory on the heap.
> 
> This indirectly fixes a snprintf truncation warning (from gcc v9.2.1):
> 
> bpf.c: In function ‘bpf_get_work_dir’:
> bpf.c:784:49: warning: ‘snprintf’ output may be truncated before the last format character [-Wformat-truncation=]
>   784 |  snprintf(bpf_wrk_dir, sizeof(bpf_wrk_dir), "%s/", mnt);
>       |                                                 ^
> bpf.c:784:2: note: ‘snprintf’ output between 2 and 4097 bytes into a destination of size 4096
>   784 |  snprintf(bpf_wrk_dir, sizeof(bpf_wrk_dir), "%s/", mnt);
>       |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Fixes: e42256699cac ("bpf: make tc's bpf loader generic and move into lib")
> Signed-off-by: Andrea Claudi <aclaudi@redhat.com>
> ---
>  lib/bpf.c | 95 +++++++++++++++++++++++++++++++++----------------------
>  1 file changed, 57 insertions(+), 38 deletions(-)
> 
> diff --git a/lib/bpf.c b/lib/bpf.c
> index 7d2a322ffbaec..18e0334d3f11b 100644
> --- a/lib/bpf.c
> +++ b/lib/bpf.c
> @@ -406,13 +406,14 @@ 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[PATH_MAX], buff[4096];
> +	char *file, buff[4096];
>  	FILE *fp;
>  
> -	snprintf(file, sizeof(file), "/proc/%d/fdinfo/%d", getpid(), fd);
> +	asprintf(&file, "/proc/%d/fdinfo/%d", getpid(), fd);

Thanks for taking this on.

From 'man asprintf':
  "If  memory  allocation  wasn't  possible, or some other error occurs,
these functions will return -1, and the contents of strp are undefined."

ie., you should check the return code of asprintf and make sure the
pointer passed is always initialized to NULL (static ones do not need
the init).

Patch
diff mbox series

diff --git a/lib/bpf.c b/lib/bpf.c
index 7d2a322ffbaec..18e0334d3f11b 100644
--- a/lib/bpf.c
+++ b/lib/bpf.c
@@ -406,13 +406,14 @@  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[PATH_MAX], buff[4096];
+	char *file, buff[4096];
 	FILE *fp;
 
-	snprintf(file, sizeof(file), "/proc/%d/fdinfo/%d", getpid(), fd);
+	asprintf(&file, "/proc/%d/fdinfo/%d", getpid(), fd);
 	memset(map, 0, sizeof(*map));
 
 	fp = fopen(file, "r");
+	free(file);
 	if (!fp) {
 		fprintf(stderr, "No procfs support?!\n");
 		return -EIO;
@@ -600,7 +601,7 @@  int bpf_trace_pipe(void)
 		0,
 	};
 	int fd_in, fd_out = STDERR_FILENO;
-	char tpipe[PATH_MAX];
+	char *tpipe;
 	const char *mnt;
 
 	mnt = bpf_find_mntpt("tracefs", TRACEFS_MAGIC, tracefs_mnt,
@@ -610,9 +611,10 @@  int bpf_trace_pipe(void)
 		return -1;
 	}
 
-	snprintf(tpipe, sizeof(tpipe), "%s/trace_pipe", mnt);
+	asprintf(&tpipe, "%s/trace_pipe", mnt);
 
 	fd_in = open(tpipe, O_RDONLY);
+	free(tpipe);
 	if (fd_in < 0)
 		return -1;
 
@@ -633,37 +635,42 @@  int bpf_trace_pipe(void)
 
 static int bpf_gen_global(const char *bpf_sub_dir)
 {
-	char bpf_glo_dir[PATH_MAX];
+	char *bpf_glo_dir;
 	int ret;
 
-	snprintf(bpf_glo_dir, sizeof(bpf_glo_dir), "%s/%s/",
-		 bpf_sub_dir, BPF_DIR_GLOBALS);
+	asprintf(&bpf_glo_dir, "%s/%s/", bpf_sub_dir, BPF_DIR_GLOBALS);
 
 	ret = mkdir(bpf_glo_dir, S_IRWXU);
 	if (ret && errno != EEXIST) {
 		fprintf(stderr, "mkdir %s failed: %s\n", bpf_glo_dir,
 			strerror(errno));
-		return ret;
+		goto out;
 	}
 
-	return 0;
+	ret = 0;
+out:
+	free(bpf_glo_dir);
+	return ret;
 }
 
 static int bpf_gen_master(const char *base, const char *name)
 {
-	char bpf_sub_dir[PATH_MAX + NAME_MAX + 1];
+	char *bpf_sub_dir;
 	int ret;
 
-	snprintf(bpf_sub_dir, sizeof(bpf_sub_dir), "%s%s/", base, name);
+	asprintf(&bpf_sub_dir, "%s%s/", base, name);
 
 	ret = mkdir(bpf_sub_dir, S_IRWXU);
 	if (ret && errno != EEXIST) {
 		fprintf(stderr, "mkdir %s failed: %s\n", bpf_sub_dir,
 			strerror(errno));
-		return ret;
+		goto out;
 	}
 
-	return bpf_gen_global(bpf_sub_dir);
+	ret = bpf_gen_global(bpf_sub_dir);
+out:
+	free(bpf_sub_dir);
+	return ret;
 }
 
 static int bpf_slave_via_bind_mnt(const char *full_name,
@@ -692,13 +699,13 @@  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[PATH_MAX + NAME_MAX + 1];
-	char bpf_sub_dir[PATH_MAX + NAME_MAX];
+	char *bpf_lnk_dir;
+	char *bpf_sub_dir;
 	struct stat sb = {};
 	int ret;
 
-	snprintf(bpf_lnk_dir, sizeof(bpf_lnk_dir), "%s%s/", base, link);
-	snprintf(bpf_sub_dir, sizeof(bpf_sub_dir), "%s%s",  base, name);
+	asprintf(&bpf_lnk_dir, "%s%s/", base, link);
+	asprintf(&bpf_sub_dir, "%s%s",  base, name);
 
 	ret = symlink(bpf_lnk_dir, bpf_sub_dir);
 	if (ret) {
@@ -706,25 +713,30 @@  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));
-				return ret;
+				goto out;
 			}
 
-			return bpf_slave_via_bind_mnt(bpf_sub_dir,
-						      bpf_lnk_dir);
+			ret = bpf_slave_via_bind_mnt(bpf_sub_dir, bpf_lnk_dir);
+			goto out;
 		}
 
 		ret = lstat(bpf_sub_dir, &sb);
 		if (ret) {
 			fprintf(stderr, "lstat %s failed: %s\n",
 				bpf_sub_dir, strerror(errno));
-			return ret;
+			goto out;
 		}
 
-		if ((sb.st_mode & S_IFMT) != S_IFLNK)
-			return bpf_gen_global(bpf_sub_dir);
+		if ((sb.st_mode & S_IFMT) != S_IFLNK) {
+			ret = bpf_gen_global(bpf_sub_dir);
+			goto out;
+		}
 	}
 
-	return 0;
+out:
+	free(bpf_lnk_dir);
+	free(bpf_sub_dir);
+	return ret;
 }
 
 static int bpf_gen_hierarchy(const char *base)
@@ -742,7 +754,7 @@  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[PATH_MAX];
+	static char *bpf_wrk_dir;
 	static const char *mnt;
 	static bool bpf_mnt_cached;
 	const char *mnt_env = getenv(BPF_ENV_MNT);
@@ -781,7 +793,7 @@  static const char *bpf_get_work_dir(enum bpf_prog_type type)
 		}
 	}
 
-	snprintf(bpf_wrk_dir, sizeof(bpf_wrk_dir), "%s/", mnt);
+	asprintf(&bpf_wrk_dir, "%s/", mnt);
 
 	ret = bpf_gen_hierarchy(bpf_wrk_dir);
 	if (ret) {
@@ -1438,29 +1450,31 @@  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[PATH_MAX];
+	char *tmp;
 	int ret;
 
-	snprintf(tmp, sizeof(tmp), "%s/%s", bpf_get_work_dir(ctx->type),
-		 ctx->obj_uid);
+	asprintf(&tmp, "%s/%s", bpf_get_work_dir(ctx->type), ctx->obj_uid);
 
 	ret = mkdir(tmp, S_IRWXU);
 	if (ret && errno != EEXIST) {
 		fprintf(stderr, "mkdir %s failed: %s\n", tmp, strerror(errno));
-		return ret;
+		goto out;
 	}
 
-	return 0;
+	ret = 0;
+out:
+	free(tmp);
+	return ret;
 }
 
 static int bpf_make_custom_path(const struct bpf_elf_ctx *ctx,
 				const char *todo)
 {
-	char tmp[PATH_MAX], rem[PATH_MAX], *sub;
+	char *tmp, *rem, *sub;
 	int ret;
 
-	snprintf(tmp, sizeof(tmp), "%s/../", bpf_get_work_dir(ctx->type));
-	snprintf(rem, sizeof(rem), "%s/", todo);
+	asprintf(&tmp, "%s/../", bpf_get_work_dir(ctx->type));
+	asprintf(&rem, "%s/", todo);
 	sub = strtok(rem, "/");
 
 	while (sub) {
@@ -1474,13 +1488,17 @@  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));
-			return ret;
+			goto out;
 		}
 
 		sub = strtok(NULL, "/");
 	}
 
-	return 0;
+	ret = 0;
+out:
+	free(rem);
+	free(tmp);
+	return ret;
 }
 
 static int bpf_place_pinned(int fd, const char *name,
@@ -2581,14 +2599,15 @@  struct bpf_jited_aux {
 
 static int bpf_derive_prog_from_fdinfo(int fd, struct bpf_prog_data *prog)
 {
-	char file[PATH_MAX], buff[4096];
+	char *file, buff[4096];
 	unsigned int val;
 	FILE *fp;
 
-	snprintf(file, sizeof(file), "/proc/%d/fdinfo/%d", getpid(), fd);
+	asprintf(&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;