[PATCH] Fix "mount <address>" and MNT_CURSOR entries.
by Aureau, Georges (Kernel Tools ERT)
Fix "mount <address>" and MNT_CURSOR entries:
1/ "mount <address>" is failing on kernels without "super_block.s_files":
crash> mount ff35d61d80200000
mount: the super_block.s_files linked list does not exist in this kernel
mount: -f option not supported or applicable on this architecture or kernel
The MOUNT_PRINT_FILES flags should only be passed when "super_block.s_files"
is available.
2/ "mount" is not skipping MNT_CURSOR entries (kernel >= 5.8):
crash> mount > mount.out
WARNING: cannot get super_block from vfsmnt: 0xff35d65eb1cc1820
crash> struct mount.mnt.mnt_sb,mnt.mnt_flags -x 0xff35d65eb1cc1820
mnt.mnt_sb = 0x0,
mnt.mnt_flags = 0x10000000,
When crashing with running "findmnt" commands, the mount list will
have entries with mnt.mnt_flags==MNT_CURSOR (and mnt.mnt_sb==NULL).
Such entries should be skipped without errors.
Signed-off-by: Georges Aureau <georges.aureau(a)hpe.com>
--
defs.h | 1 +
filesys.c | 16 +++++++++++++++-
symbols.c | 2 ++
3 files changed, 18 insertions(+), 1 deletion(-)
diff --git a/defs.h b/defs.h
index 156ac02..9e37f26 100644
--- a/defs.h
+++ b/defs.h
@@ -1508,6 +1508,7 @@ struct offset_table { /* stash of commonly-used offsets */
long vfsmount_mnt_devname;
long vfsmount_mnt_dirname;
long vfsmount_mnt_sb;
+ long vfsmount_mnt_flags;
long vfsmount_mnt_list;
long vfsmount_mnt_mountpoint;
long vfsmount_mnt_parent;
diff --git a/filesys.c b/filesys.c
index 8d13807..7439c2e 100644
--- a/filesys.c
+++ b/filesys.c
@@ -1296,7 +1296,7 @@ cmd_mount(void)
* through it for each search argument entered.
*/
open_tmpfile();
- show_mounts(0, MOUNT_PRINT_FILES |
+ show_mounts(0, (VALID_MEMBER(super_block_s_files) ? MOUNT_PRINT_FILES : 0) |
(VALID_MEMBER(super_block_s_dirty) ? MOUNT_PRINT_INODES : 0),
namespace_context);
@@ -1371,6 +1371,14 @@ cmd_mount(void)
* Do the work for cmd_mount();
*/
+/* For kernels >= 5.8, we need to skip MNT_CURSOR entries.
+ * See https://elixir.bootlin.com/linux/v5.8/source/include/linux/mount.h#L73
+ * https://elixir.bootlin.com/linux/v5.8/source/fs/namespace.c#L661
+ * https://elixir.bootlin.com/linux/v5.8/source/fs/namespace.c#L690
+ * https://elixir.bootlin.com/linux/v5.8/source/fs/proc_namespace.c#L283
+ */
+#define MNT_CURSOR 0x10000000
+
static void
show_mounts(ulong one_vfsmount, int flags, struct task_context *namespace_context)
{
@@ -1492,6 +1500,11 @@ show_mounts(ulong one_vfsmount, int flags, struct task_context *namespace_contex
sbp = ULONG(vfsmount_buf + OFFSET(vfsmount_mnt_sb));
if (!IS_KVADDR(sbp)) {
+ if (sbp == 0 && VALID_MEMBER(vfsmount_mnt_flags)) {
+ int mnt_flags = INT(vfsmount_buf + OFFSET(vfsmount_mnt_flags));
+ if (mnt_flags == MNT_CURSOR)
+ continue;
+ }
error(WARNING, "cannot get super_block from vfsmnt: 0x%lx\n", *vfsmnt);
continue;
}
@@ -2070,6 +2083,7 @@ vfs_init(void)
MEMBER_OFFSET_INIT(mount_mnt_devname, "mount", "mnt_devname");
MEMBER_OFFSET_INIT(vfsmount_mnt_dirname, "vfsmount", "mnt_dirname");
MEMBER_OFFSET_INIT(vfsmount_mnt_sb, "vfsmount", "mnt_sb");
+ MEMBER_OFFSET_INIT(vfsmount_mnt_flags, "vfsmount", "mnt_flags");
MEMBER_OFFSET_INIT(vfsmount_mnt_list, "vfsmount", "mnt_list");
if (INVALID_MEMBER(vfsmount_mnt_devname))
MEMBER_OFFSET_INIT(mount_mnt_list, "mount", "mnt_list");
diff --git a/symbols.c b/symbols.c
index 112bcc6..92098a8 100644
--- a/symbols.c
+++ b/symbols.c
@@ -10685,6 +10685,8 @@ dump_offset_table(char *spec, ulong makestruct)
OFFSET(vfsmount_mnt_dirname));
fprintf(fp, " vfsmount_mnt_sb: %ld\n",
OFFSET(vfsmount_mnt_sb));
+ fprintf(fp, " vfsmount_mnt_flags: %ld\n",
+ OFFSET(vfsmount_mnt_flags));
fprintf(fp, " vfsmount_mnt_list: %ld\n",
OFFSET(vfsmount_mnt_list));
fprintf(fp, " vfsmount_mnt_mountpoint: %ld\n",
