[RFC,20/24] libselinux: check for stream rewind failures

Commit Message

Christian Göttsche Aug. 11, 2023, 4:27 p.m. UTC

Use fseek(3) instead of rewind(3) to detect failures.

Drop the final rewind in digest_add_specfile(), since all callers are
going to close the stream without any further action.

Signed-off-by: Christian Göttsche <[e-mail]>
---
 libselinux/src/is_customizable_type.c   |  7 ++++++-
 libselinux/src/label_backends_android.c |  5 ++++-
 libselinux/src/label_file.c             | 16 +++++++++++++---
 libselinux/src/label_media.c            |  5 ++++-
 libselinux/src/label_support.c          |  5 +++--
 libselinux/src/label_x.c                |  5 ++++-
 6 files changed, 34 insertions(+), 9 deletions(-)

Patch

diff --git a/libselinux/src/is_customizable_type.c b/libselinux/src/is_customizable_type.c
index f83e1e83..9be50174 100644
--- a/libselinux/src/is_customizable_type.c
+++ b/libselinux/src/is_customizable_type.c
@@ -31,7 +31,12 @@  static void customizable_init(void)
 	while (fgets_unlocked(buf, selinux_page_size, fp) && ctr < UINT_MAX) {
 		ctr++;
 	}
-	rewind(fp);
+
+	if (fseek(fp, 0L, SEEK_SET) == -1) {
+		fclose(fp);
+		return;
+	}
+
 	if (ctr) {
 		list =
 		    (char **) calloc(sizeof(char *),
diff --git a/libselinux/src/label_backends_android.c b/libselinux/src/label_backends_android.c
index c2d78360..6494f3cd 100644
--- a/libselinux/src/label_backends_android.c
+++ b/libselinux/src/label_backends_android.c
@@ -208,7 +208,10 @@  static int init(struct selabel_handle *rec, const struct selinux_opt *opts,
 				goto finish;
 
 			maxnspec = data->nspec;
-			rewind(fp);
+
+			status = fseek(fp, 0L, SEEK_SET);
+			if (status == -1)
+				goto finish;
 		}
 	}
 
diff --git a/libselinux/src/label_file.c b/libselinux/src/label_file.c
index 471fd56b..a5677411 100644
--- a/libselinux/src/label_file.c
+++ b/libselinux/src/label_file.c
@@ -519,12 +519,16 @@  static char *rolling_append(char *current, const char *suffix, size_t max)
 	return current;
 }
 
-static bool fcontext_is_binary(FILE *fp)
+static int fcontext_is_binary(FILE *fp)
 {
 	uint32_t magic;
+	int rc;
 
 	size_t len = fread(&magic, sizeof(magic), 1, fp);
-	rewind(fp);
+
+	rc = fseek(fp, 0L, SEEK_SET);
+	if (rc == -1)
+		return -1;
 
 	return (len && (magic == SELINUX_MAGIC_COMPILED_FCONTEXT));
 }
@@ -622,7 +626,13 @@  static int process_file(const char *path, const char *suffix,
 		if (fp == NULL)
 			return -1;
 
-		rc = fcontext_is_binary(fp) ?
+		rc = fcontext_is_binary(fp);
+		if (rc < 0) {
+			(void) fclose(fp);
+			return -1;
+		}
+
+		rc = rc ?
 				load_mmap(fp, sb.st_size, rec, found_path) :
 				process_text_file(fp, rec, found_path);
 		if (!rc)
diff --git a/libselinux/src/label_media.c b/libselinux/src/label_media.c
index f09461ab..b3443b47 100644
--- a/libselinux/src/label_media.c
+++ b/libselinux/src/label_media.c
@@ -130,7 +130,10 @@  static int init(struct selabel_handle *rec, const struct selinux_opt *opts,
 				goto finish;
 			memset(data->spec_arr, 0, sizeof(spec_t)*data->nspec);
 			maxnspec = data->nspec;
-			rewind(fp);
+
+			status = fseek(fp, 0L, SEEK_SET);
+			if (status == -1)
+				goto finish;
 		}
 	}
 	free(line_buf);
diff --git a/libselinux/src/label_support.c b/libselinux/src/label_support.c
index 94fb6697..f7ab9292 100644
--- a/libselinux/src/label_support.c
+++ b/libselinux/src/label_support.c
@@ -174,12 +174,13 @@  int  digest_add_specfile(struct selabel_digest *digest, FILE *fp,
 	digest->hashbuf = tmp_buf;
 
 	if (fp) {
-		rewind(fp);
+		if (fseek(fp, 0L, SEEK_SET) == -1)
+			return -1;
+
 		if (fread(digest->hashbuf + (digest->hashbuf_size - buf_len),
 					    1, buf_len, fp) != buf_len)
 			return -1;
 
-		rewind(fp);
 	} else if (from_addr) {
 		tmp_buf = memcpy(digest->hashbuf +
 				    (digest->hashbuf_size - buf_len),
diff --git a/libselinux/src/label_x.c b/libselinux/src/label_x.c
index e80bf107..e15190ca 100644
--- a/libselinux/src/label_x.c
+++ b/libselinux/src/label_x.c
@@ -157,7 +157,10 @@  static int init(struct selabel_handle *rec, const struct selinux_opt *opts,
 				goto finish;
 			memset(data->spec_arr, 0, sizeof(spec_t)*data->nspec);
 			maxnspec = data->nspec;
-			rewind(fp);
+
+			status = fseek(fp, 0L, SEEK_SET);
+			if (status == -1)
+				goto finish;
 		}
 	}
 	free(line_buf);