eal/linux: fix hugetlbfs sub-directories discovery

[ upstream commit f9d1ef28619a2dd16cafca36f5a5ca6d3315c5fc ]

The code added for allowing --huge-dir to specify hugetlbfs
sub-directories has a bug where it incorrectly matches mounts that
contain a prefix of the specified --huge-dir.

Consider --huge-dir=/dev/hugepages1G is passed to rte_eal_init. Given
the following hugetlbfs mounts

$ mount | grep hugetlbfs
hugetlbfs on /dev/hugepages type hugetlbfs (rw,relatime,pagesize=2M)
hugetlbfs on /dev/hugepages1G type hugetlbfs (rw,relatime,pagesize=1024M)
hugetlbfs on /mnt/huge type hugetlbfs (rw,relatime,pagesize=2M)

get_hugepage_dir is first called with hugepage_sz=2097152. While
iterating over all mount points, /dev/hugepages is incorrectly
determined to be a match because it's a prefix of --huge-dir. The caller
then obtains an exclusive lock on --huge-dir.

In the next call to get_hugepage_dir, hugepage_sz=1073741824. This call
correctly determines /dev/hugepages1G is a match. The caller again
attempts to obtain an exclusive lock on --huge-dir and deadlocks because
it's already holding a lock.

This has been corrected by ensuring any matched mount point is either an
exact match or a parent path of --huge-dir.

Fixes: 24d5a1c ("eal/linux: allow hugetlbfs sub-directories")

Signed-off-by: Ashish Sadanandan <ashish.sadanandan@gmail.com>
Reviewed-by: John Levon <john.levon@nutanix.com>
Tested-by: Julien Meunier <julien.meunier@nokia.com>

lib/eal/linux/eal_hugepage_info.c

@@ -217,6 +217,8 @@ get_hugepage_dir(uint64_t hugepage_sz, char *hugedir, int len)
 	char buf[BUFSIZ];
 	const struct internal_config *internal_conf =
 		eal_get_internal_configuration();
+	const size_t hugepage_dir_len = (internal_conf->hugepage_dir != NULL) ?
+		strlen(internal_conf->hugepage_dir) : 0;
 	struct stat st;
 
 	/*
@@ -236,6 +238,7 @@ get_hugepage_dir(uint64_t hugepage_sz, char *hugedir, int len)
 
 	while (fgets(buf, sizeof(buf), fd)){
 		const char *pagesz_str;
+		size_t mountpt_len = 0;
 
 		if (rte_strsplit(buf, sizeof(buf), splitstr, _FIELDNAME_MAX,
 				split_tok) != _FIELDNAME_MAX) {
@@ -268,20 +271,24 @@ get_hugepage_dir(uint64_t hugepage_sz, char *hugedir, int len)
 			break;
 		}
 
+		mountpt_len = strlen(splitstr[MOUNTPT]);
+
 		/*
-		 * Ignore any mount that doesn't contain the --huge-dir
-		 * directory.
+		 * Ignore any mount that doesn't contain the --huge-dir directory
+		 * or where mount point is not a parent path of --huge-dir
 		 */
 		if (strncmp(internal_conf->hugepage_dir, splitstr[MOUNTPT],
-			strlen(splitstr[MOUNTPT])) != 0) {
+				mountpt_len) != 0 ||
+			(hugepage_dir_len > mountpt_len &&
+				internal_conf->hugepage_dir[mountpt_len] != '/')) {
 			continue;
 		}
 
 		/*
 		 * We found a match, but only prefer it if it's a longer match
 		 * (so /mnt/1 is preferred over /mnt for matching /mnt/1/2)).
 		 */
-		if (strlen(splitstr[MOUNTPT]) > strlen(found))
+		if (mountpt_len > strlen(found))
 			strlcpy(found, splitstr[MOUNTPT], len);
 	} /* end while fgets */