From 397aaad6da5c4bfb160adca7a68f865086f2ed0a Mon Sep 17 00:00:00 2001 From: Franck Bui Date: Thu, 30 Sep 2021 14:05:36 +0200 Subject: [PATCH] mount-util: fix fd_is_mount_point() when both the parent and directory are network fs The second call to name_to_handle_at_loop() didn't check for the specific errors that can happen when the parent dir is mounted by nfs and instead of falling back like it's done for the child dir, fd_is_mount_point() failed in this case. (cherry picked from commit 964ccab8286a7e75d7e9107f574f5cb23752bd5d) Resolves: #2015057 --- src/basic/mount-util.c | 71 ++++++++++++++++++++++++------------------ 1 file changed, 41 insertions(+), 30 deletions(-) diff --git a/src/basic/mount-util.c b/src/basic/mount-util.c index 45348bf878..0c709001be 100644 --- a/src/basic/mount-util.c +++ b/src/basic/mount-util.c @@ -139,6 +139,19 @@ static int fd_fdinfo_mnt_id(int fd, const char *filename, int flags, int *mnt_id return safe_atoi(p, mnt_id); } +static bool is_name_to_handle_at_fatal_error(int err) { + /* name_to_handle_at() can return "acceptable" errors that are due to the context. For + * example the kernel does not support name_to_handle_at() at all (ENOSYS), or the syscall + * was blocked (EACCES/EPERM; maybe through seccomp, because we are running inside of a + * container), or the mount point is not triggered yet (EOVERFLOW, think nfs4), or some + * general name_to_handle_at() flakiness (EINVAL). However other errors are not supposed to + * happen and therefore are considered fatal ones. */ + + assert(err < 0); + + return !IN_SET(err, -EOPNOTSUPP, -ENOSYS, -EACCES, -EPERM, -EOVERFLOW, -EINVAL); +} + int fd_is_mount_point(int fd, const char *filename, int flags) { _cleanup_free_ struct file_handle *h = NULL, *h_parent = NULL; int mount_id = -1, mount_id_parent = -1; @@ -173,42 +186,40 @@ int fd_is_mount_point(int fd, const char *filename, int flags) { * real mounts of their own. */ r = name_to_handle_at_loop(fd, filename, &h, &mount_id, flags); - if (IN_SET(r, -ENOSYS, -EACCES, -EPERM, -EOVERFLOW, -EINVAL)) - /* This kernel does not support name_to_handle_at() at all (ENOSYS), or the syscall was blocked - * (EACCES/EPERM; maybe through seccomp, because we are running inside of a container?), or the mount - * point is not triggered yet (EOVERFLOW, think nfs4), or some general name_to_handle_at() flakiness - * (EINVAL): fall back to simpler logic. */ - goto fallback_fdinfo; - else if (r == -EOPNOTSUPP) - /* This kernel or file system does not support name_to_handle_at(), hence let's see if the upper fs - * supports it (in which case it is a mount point), otherwise fallback to the traditional stat() - * logic */ + if (r < 0) { + if (is_name_to_handle_at_fatal_error(r)) + return r; + if (r != -EOPNOTSUPP) + goto fallback_fdinfo; + + /* This kernel or file system does not support name_to_handle_at(), hence let's see + * if the upper fs supports it (in which case it is a mount point), otherwise fall + * back to the traditional stat() logic */ nosupp = true; - else if (r < 0) - return r; + } r = name_to_handle_at_loop(fd, "", &h_parent, &mount_id_parent, AT_EMPTY_PATH); - if (r == -EOPNOTSUPP) { + if (r < 0) { + if (is_name_to_handle_at_fatal_error(r)) + return r; + if (r != -EOPNOTSUPP) + goto fallback_fdinfo; if (nosupp) - /* Neither parent nor child do name_to_handle_at()? We have no choice but to fall back. */ + /* Both the parent and the directory can't do name_to_handle_at() */ goto fallback_fdinfo; - else - /* The parent can't do name_to_handle_at() but the directory we are interested in can? If so, - * it must be a mount point. */ - return 1; - } else if (r < 0) - return r; - /* The parent can do name_to_handle_at() but the - * directory we are interested in can't? If so, it - * must be a mount point. */ + /* The parent can't do name_to_handle_at() but the directory we are + * interested in can? If so, it must be a mount point. */ + return 1; + } + + /* The parent can do name_to_handle_at() but the directory we are interested in can't? If + * so, it must be a mount point. */ if (nosupp) return 1; - /* If the file handle for the directory we are - * interested in and its parent are identical, we - * assume this is the root directory, which is a mount - * point. */ + /* If the file handle for the directory we are interested in and its parent are identical, + * we assume this is the root directory, which is a mount point. */ if (h->handle_bytes == h_parent->handle_bytes && h->handle_type == h_parent->handle_type && @@ -300,10 +311,10 @@ int path_get_mnt_id(const char *path, int *ret) { int r; r = name_to_handle_at_loop(AT_FDCWD, path, NULL, ret, 0); - if (IN_SET(r, -EOPNOTSUPP, -ENOSYS, -EACCES, -EPERM, -EOVERFLOW, -EINVAL)) /* kernel/fs don't support this, or seccomp blocks access, or untriggered mount, or name_to_handle_at() is flaky */ - return fd_fdinfo_mnt_id(AT_FDCWD, path, 0, ret); + if (r == 0 || is_name_to_handle_at_fatal_error(r)) + return r; - return r; + return fd_fdinfo_mnt_id(AT_FDCWD, path, 0, ret); } int umount_recursive(const char *prefix, int flags) {