[PATCH 1/1] eal/linux: reject mountpt shorter than --huge-dir

[Ashish Sadanandan <ashish.sadanandan@gmail.com>]

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 rejecting the mount point being considered if
its length is smaller than the specified --huge-dir.

Fixes: 24d5a1ce6b85 ("eal/linux: allow hugetlbfs sub-directories")
Cc: john.levon@nutanix.com
Cc: stable@dpdk.org
---
 lib/eal/linux/eal_hugepage_info.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/lib/eal/linux/eal_hugepage_info.c b/lib/eal/linux/eal_hugepage_info.c
index a1b6cb31ff..fcc3d82fdf 100644
--- a/lib/eal/linux/eal_hugepage_info.c
+++ b/lib/eal/linux/eal_hugepage_info.c
@@ -269,16 +269,19 @@ get_hugepage_dir(uint64_t hugepage_sz, char *hugedir, int len)
 		 * Ignore any mount that doesn't contain the --huge-dir
 		 * directory.
 		 */
-		if (strncmp(internal_conf->hugepage_dir, splitstr[MOUNTPT],
-			strlen(splitstr[MOUNTPT])) != 0) {
+		size_t mountpt_len = strlen(splitstr[MOUNTPT]);
+
+		if (strlen(internal_conf->hugepage_dir) > mountpt_len)
+			continue;
+		else if (strncmp(internal_conf->hugepage_dir, splitstr[MOUNTPT],
+			mountpt_len) != 0)
 			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 */
 
-- 
2.27.0