[apparmor] [PATCH 4/6] libapparmor: Detect errors when splitting confinement contexts

[Tyler Hicks]

The parse_confinement_mode() function returned NULL when a confinement
mode was not present (unconfined) and when it could not properly parse
the confinement context. The two situations should be differentiated
since the latter should be treated as an error.

This patch reworks parse_confinement_mode() to split a confinement
context and, optionally, assign the mode string. If a parsing error is
encountered, NULL is returned to indicate error.

Signed-off-by: Tyler Hicks <tyhicks at canonical.com>
---
 libraries/libapparmor/src/kernel.c | 48 +++++++++++++++++++++++++-------------
 1 file changed, 32 insertions(+), 16 deletions(-)

diff --git a/libraries/libapparmor/src/kernel.c b/libraries/libapparmor/src/kernel.c
index b167050..b792ac2 100644
--- a/libraries/libapparmor/src/kernel.c
+++ b/libraries/libapparmor/src/kernel.c
@@ -168,18 +168,29 @@ static bool parse_unconfined(char *con, int size)
 }
 
 /**
- * parse_confinement_mode - get the mode from the confinement context
+ * splitcon - split the confinement context into a label and mode
  * @con: the confinement context
  * @size: size of the confinement context (not including the NUL terminator)
+ * @mode: if non-NULL and a mode is present, will point to mode string in @con
+ *  on success
  *
- * Modifies con to NUL-terminate the label string and the mode string.
+ * Modifies the @con string to split it into separate label and mode strings.
+ * The @mode argument is optional. If @mode is NULL, @con will still be split
+ * between the label and mode (if present) but @mode will not be set.
  *
- * Returns: a pointer to the NUL-terminated mode inside the confinement context
- * or NULL if the mode was not found
+ * Returns: a pointer to the label string or NULL on error
  */
-static char *parse_confinement_mode(char *con, int size)
+static char *splitcon(char *con, int size, char **mode)
 {
-	if (!parse_unconfined(con, size) && size > 3 && con[size - 1] == ')') {
+	char *label = NULL;
+	char *mode_str = NULL;
+
+	if (parse_unconfined(con, size)) {
+		label = con;
+		goto out;
+	}
+
+	if (size > 3 && con[size - 1] == ')') {
 		int pos = size - 2;
 
 		while (pos > 0 && !(con[pos] == ' ' && con[pos + 1] == '('))
@@ -187,10 +198,14 @@ static char *parse_confinement_mode(char *con, int size)
 		if (pos > 0) {
 			con[pos] = 0; /* overwrite ' ' */
 			con[size - 1] = 0; /* overwrite trailing ) */
-			return &con[pos + 2]; /* skip '(' */
+			mode_str = &con[pos + 2]; /* skip '(' */
+			label = con;
 		}
 	}
-	return NULL;
+out:
+	if (mode)
+		*mode = mode_str;
+	return label;
 }
 
 /**
@@ -209,7 +224,6 @@ int aa_getprocattr_raw(pid_t tid, const char *attr, char *buf, int len,
 	int rc = -1;
 	int fd, ret;
 	char *tmp = NULL;
-	char *mode_str;
 	int size = 0;
 
 	if (!buf || len <= 0) {
@@ -265,9 +279,10 @@ int aa_getprocattr_raw(pid_t tid, const char *attr, char *buf, int len,
 		}
 
 		*nul = 0;
-		mode_str = parse_confinement_mode(buf, nul - buf);
-		if (mode)
-			*mode = mode_str;
+		if (splitcon(buf, nul - buf, mode) != buf) {
+			errno = EINVAL;
+			goto out2;
+		}
 	}
 	rc = size;
 
@@ -606,7 +621,6 @@ int aa_getcon(char **label, char **mode)
 int aa_getpeercon_raw(int fd, char *buf, int *len, char **mode)
 {
 	socklen_t optlen = *len;
-	char *mode_str;
 	int rc;
 
 	if (optlen <= 0 || buf == NULL) {
@@ -632,9 +646,11 @@ int aa_getpeercon_raw(int fd, char *buf, int *len, char **mode)
 		}
 	}
 
-	mode_str = parse_confinement_mode(buf, optlen - 1);
-	if (mode)
-		*mode = mode_str;
+	if (splitcon(buf, optlen - 1, mode) != buf) {
+		rc = -1;
+		errno = EINVAL;
+		goto out;
+	}
 
 	rc = optlen;
 out:
-- 
2.1.4