From: Theodore Ts'o <tytso@mit.edu>
Date: Sat, 24 Jul 2021 16:55:28 +0000 (-0400)
Subject: libext2fs: avoid unnecessary stat(2) calls on mountpoints
X-Git-Tag: v1.46.3~9
X-Git-Url: https://git.whamcloud.com/?a=commitdiff_plain;h=ddee43e8e847b25148d694bb5dbec633729e975b;p=tools%2Fe2fsprogs.git

libext2fs: avoid unnecessary stat(2) calls on mountpoints

If the device name in the mtab or /proc/mounts file does not match
with the device passed into ext2fs_check_if_mounted() or
ext2fs_check_mount_point(), skip the stat(2) call on the mountpoint,
since we never use the results of the stat(2) in that case.  Not only
does this provide a slight performance win, but it the stat calls on
the mountpoints could potentially trigger some SELinux denials that
could stress some sysadmins out.

Google-Bug-Id:  193137337
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---

diff --git a/lib/ext2fs/ismounted.c b/lib/ext2fs/ismounted.c
index 46d330d..c9e6a9d 100644
--- a/lib/ext2fs/ismounted.c
+++ b/lib/ext2fs/ismounted.c
@@ -128,14 +128,14 @@ static errcode_t check_mntent_file(const char *mtab_file, const char *file,
 	while ((mnt = getmntent (f)) != NULL) {
 		if (mnt->mnt_fsname[0] != '/')
 			continue;
-		if (stat(mnt->mnt_dir, &st_buf) != 0)
-			continue;
 		if (strcmp(file, mnt->mnt_fsname) == 0) {
+			if (stat(mnt->mnt_dir, &st_buf) != 0)
+				continue;
 			if (file_rdev && (file_rdev != st_buf.st_dev)) {
 #ifdef DEBUG
 				printf("Bogus entry in %s!  "
-				       "(%s does not exist)\n",
-				       mtab_file, mnt->mnt_dir);
+				       "(%s is not mounted on %s)\n",
+				       mtab_file, file, mnt->mnt_dir);
 #endif /* DEBUG */
 				continue;
 			}