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From 996f88461c45e8620c5a8a0c958dc133bd02c50e Mon Sep 17 00:00:00 2001
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From: Jakob Unterwurzacher <jakobunt@gmail.com>
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Date: Mon, 30 Nov 2020 10:27:48 +0100
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Subject: [PATCH] mount-util: bind_remount: avoid calling statvfs
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The commit
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"util: Do not clear parent mount flags when setting up namespaces"
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introduced a statvfs call read the flags of the original mount
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and have them applied to the bind mount.
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This has two problems:
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(1) The mount flags returned by statvfs(2) do not match the flags
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accepted by mount(2). For example, the value 4096 means ST_RELATIME
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when returned by statvfs(2), but means MS_BIND when passed to mount(2).
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(2) A call to statvfs blocks indefinitely when ran against a disconnected
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network drive ( https://github.com/systemd/systemd/issues/12667 ).
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We already use libmount to parse `/proc/self/mountinfo` but did not use the
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mount flag information from there. This patch changes that to use the mount
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flags parsed by libmount instead of calling statvfs. Only if getting the
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flags through libmount fails we call statvfs.
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Fixes https://github.com/systemd/systemd/issues/12667
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(cherry picked from commit d34a40082db3ffca8de66bfa4df50951101bdae5)
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Resolves: #1885143
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---
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 src/basic/mount-util.c | 31 +++++++++++++++++++++++++++----
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 1 file changed, 27 insertions(+), 4 deletions(-)
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diff --git a/src/basic/mount-util.c b/src/basic/mount-util.c
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index bac1a25cc8..2cf98eaa84 100644
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--- a/src/basic/mount-util.c
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+++ b/src/basic/mount-util.c
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@@ -364,11 +364,34 @@ int umount_recursive(const char *prefix, int flags) {
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         return r ? r : n;
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 }
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-static int get_mount_flags(const char *path, unsigned long *flags) {
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-        struct statvfs buf;
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+/* Get the mount flags for the mountpoint at "path" from "table" */
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+static int get_mount_flags(const char *path, unsigned long *flags, struct libmnt_table *table) {
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+        struct statvfs buf = {};
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+        struct libmnt_fs *fs = NULL;
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+        const char *opts = NULL;
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+        int r = 0;
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+
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+        fs = mnt_table_find_target(table, path, MNT_ITER_FORWARD);
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+        if (fs == NULL) {
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+                log_warning("Could not find '%s' in mount table", path);
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+                goto fallback;
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+        }
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+
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+        opts = mnt_fs_get_vfs_options(fs);
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+        r = mnt_optstr_get_flags(opts, flags, mnt_get_builtin_optmap(MNT_LINUX_MAP));
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+        if (r != 0) {
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+                log_warning_errno(r, "Could not get flags for '%s': %m", path);
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+                goto fallback;
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+        }
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+        /* relatime is default and trying to set it in an unprivileged container causes EPERM */
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+        *flags &= ~MS_RELATIME;
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+        return 0;
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+
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+fallback:
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         if (statvfs(path, &buf) < 0)
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                 return -errno;
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+
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         *flags = buf.f_flag;
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         return 0;
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 }
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@@ -501,7 +524,7 @@ int bind_remount_recursive_with_mountinfo(const char *prefix, bool ro, char **bl
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                                 return -errno;
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                         orig_flags = 0;
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-                        (void) get_mount_flags(cleaned, &orig_flags);
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+                        (void) get_mount_flags(cleaned, &orig_flags, table);
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                         orig_flags &= ~MS_RDONLY;
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                         if (mount(NULL, prefix, NULL, orig_flags|MS_BIND|MS_REMOUNT|(ro ? MS_RDONLY : 0), NULL) < 0)
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@@ -535,7 +558,7 @@ int bind_remount_recursive_with_mountinfo(const char *prefix, bool ro, char **bl
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                         /* Try to reuse the original flag set */
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                         orig_flags = 0;
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-                        (void) get_mount_flags(x, &orig_flags);
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+                        (void) get_mount_flags(x, &orig_flags, table);
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                         orig_flags &= ~MS_RDONLY;
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                         if (mount(NULL, x, NULL, orig_flags|MS_BIND|MS_REMOUNT|(ro ? MS_RDONLY : 0), NULL) < 0)