[PATCH 4/6] libselinux: ensure that 4 columns are read from /proc/mounts

[Nicolas Iooss <nicolas.iooss@xxxxxxx>]

If exclude_non_seclabel_mounts() ever gets run on a kernel where
/proc/mounts only contains three columns, mount_info[3] will be used
"without being initialized in "strtok(mount_info[3], ",")" because
variable index would be 3 at the end of this loop:

    index = 0;
    item = strtok(buf, " ");
    while (item != NULL) {
        mount_info[index] = item;
        if (index == 3)
            break;
        index++;
        item = strtok(NULL, " ");
    }

Swap the condition on index and its increment so that it gets to 4 only
when there are at least four columns.

This issue has been found using clang's static analyzer.

Signed-off-by: Nicolas Iooss <nicolas.iooss@xxxxxxx>
---
 libselinux/src/selinux_restorecon.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/libselinux/src/selinux_restorecon.c b/libselinux/src/selinux_restorecon.c
index 9fdafea17de7..eefd2cf83e32 100644
--- a/libselinux/src/selinux_restorecon.c
+++ b/libselinux/src/selinux_restorecon.c
@@ -252,12 +252,12 @@ static int exclude_non_seclabel_mounts(void)
 		item = strtok(buf, " ");
 		while (item != NULL) {
 			mount_info[index] = item;
-			if (index == 3)
-				break;
 			index++;
+			if (index == 4)
+				break;
 			item = strtok(NULL, " ");
 		}
-		if (index < 3) {
+		if (index < 4) {
 			selinux_log(SELINUX_ERROR,
 				    "/proc/mounts record \"%s\" has incorrect format.\n",
 				    buf);
-- 
2.12.0

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