From db63f0e1e935ebc1e86c3d9b6a5649b79cecff34 Mon Sep 17 00:00:00 2001
From: Evan Lezar <elezar@nvidia.com>
Date: Thu, 5 Sep 2024 14:21:03 +0200
Subject: [PATCH] Skip directories and symlinks when mounting libraries

This ensures that only actual libraries from the compat folders are
mounted into the container.

Signed-off-by: Evan Lezar <elezar@nvidia.com>
---
 src/nvc_mount.c | 19 +++++++++++++++----
 src/utils.c     | 19 +++++++++++++++++--
 src/utils.h     |  1 +
 src/xfuncs.h    | 11 +++++++++++
 4 files changed, 44 insertions(+), 6 deletions(-)

diff --git a/src/nvc_mount.c b/src/nvc_mount.c
index 61564e3f..dd6e6088 100644
--- a/src/nvc_mount.c
+++ b/src/nvc_mount.c
@@ -99,9 +99,10 @@ mount_with_flags(struct error *err, const char *src, const char *dst, uid_t uid,
 static char **
 mount_files(struct error *err, const char *root, const struct nvc_container *cnt, const char *dir, char *paths[], size_t size)
 {
+        char dummy[PATH_MAX];
         char src[PATH_MAX];
         char dst[PATH_MAX];
-        mode_t mode;
+        mode_t mode, dst_mode;
         char *src_end, *dst_end, *file;
         char **mnt, **ptr;
 
@@ -124,13 +125,23 @@ mount_files(struct error *err, const char *root, const struct nvc_container *cnt
                         continue;
                 if (path_append(err, src, paths[i]) < 0)
                         goto fail;
-                if (path_append(err, dst, file) < 0)
+                if (file_mode_nofollow(err, src, &mode) < 0)
                         goto fail;
-                if (file_mode(err, src, &mode) < 0)
+                // If we encounter resolved directories or symlinks here, we raise an error.
+                if (S_ISDIR(mode) || S_ISLNK(mode)) {
+                        error_setx(err, "unexpected source file mode %o for %s", mode, paths[i]);
                         goto fail;
+                }
+                if (path_append(err, dst, file) < 0)
+                        goto fail;
+                if (file_mode_nofollow(err, dst, &dst_mode) == 0) {
+                        if (S_ISDIR(dst_mode) || S_ISLNK(dst_mode)) {
+                                error_setx(err, "unexpected destination file mode %o for %s", dst_mode, file);
+                                goto fail;
+                        }
+                };
                 if (file_create(err, dst, NULL, cnt->uid, cnt->gid, mode) < 0)
                         goto fail;
-
                 log_infof("mounting %s at %s", src, dst);
                 if (xmount(err, src, dst, NULL, MS_BIND, NULL) < 0)
                         goto fail;
diff --git a/src/utils.c b/src/utils.c
index ab9bacff..a4ba1915 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -542,9 +542,9 @@ file_create(struct error *err, const char *path, const char *data, uid_t uid, gi
         int rv = -1;
 
         // We check whether the file already exists with the required mode and skip the creation.
-        if (data == NULL && file_mode(err, path, &perm) == 0) {
+        if (data == NULL && file_mode_nofollow(err, path, &perm) == 0) {
                 if (perm == mode) {
-                        log_errf("The path %s already exists with the required mode; skipping create", path);
+                        log_warnf("The path %s already exists with the required mode; skipping create", path);
                         return (0);
                 }
         }
@@ -677,6 +677,21 @@ file_mode(struct error *err, const char *path, mode_t *mode)
         return (0);
 }
 
+// file_mode_nofollow implements the same functionality as file_mode except that
+// in that case of a symlink, the file is not followed and the mode of the
+// original file is returned.
+int
+file_mode_nofollow(struct error *err, const char *path, mode_t *mode)
+{
+        struct stat s;
+        int rv;
+
+        if (xlstat(err, path, &s) < 0)
+                return (-1);
+        *mode = s.st_mode;
+        return (0);
+}
+
 int
 file_read_line(struct error *err, const char *path, char *buf, size_t size)
 {
diff --git a/src/utils.h b/src/utils.h
index e9cedf1a..82ea199d 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -73,6 +73,7 @@ int  file_remove(struct error *, const char *);
 int  file_exists(struct error *, const char *);
 int  file_exists_at(struct error *, const char *, const char *);
 int  file_mode(struct error *, const char *, mode_t *);
+int  file_mode_nofollow(struct error *, const char *, mode_t *);
 int  file_read_line(struct error *, const char *, char *, size_t);
 int  file_read_text(struct error *, const char *, char **);
 int  file_read_uint32(struct error *, const char *, uint32_t *);
diff --git a/src/xfuncs.h b/src/xfuncs.h
index 2c3f3f90..8d5e5f2b 100644
--- a/src/xfuncs.h
+++ b/src/xfuncs.h
@@ -22,6 +22,7 @@ static inline void xclose(int);
 static inline int  xopen(struct error *, const char *, int);
 static inline void *xcalloc(struct error *, size_t, size_t);
 static inline int  xstat(struct error *, const char *, struct stat *);
+static inline int  xlstat(struct error *, const char *, struct stat *);
 static inline FILE *xfopen(struct error *, const char *, const char *);
 static inline char *xstrdup(struct error *, const char *);
 static inline int  xasprintf(struct error *, char **, const char *, ...)
@@ -74,6 +75,16 @@ xstat(struct error *err, const char *path, struct stat *buf)
         return (rv);
 }
 
+static inline int
+xlstat(struct error *err, const char *path, struct stat *buf)
+{
+        int rv;
+
+        if ((rv = lstat(path, buf)) < 0)
+                error_set(err, "lstat failed: %s", path);
+        return (rv);
+}
+
 static inline FILE *
 xfopen(struct error *err, const char *path, const char *mode)
 {