[PATCH AUTOSEL 6.1 07/21] fs: Use CHECK_DATA_CORRUPTION() when kernel bugs are detected

Sasha Levin
2023-02-26T03:45:23Z

From: Jann Horn <jannh@google.com>

[ Upstream commit 47d586913f2abec4d240bae33417f537fda987ec ]

Currently, filp_close() and generic_shutdown_super() use printk() to log
messages when bugs are detected. This is problematic because infrastructure
like syzkaller has no idea that this message indicates a bug.
In addition, some people explicitly want their kernels to BUG() when kernel
data corruption has been detected (CONFIG_BUG_ON_DATA_CORRUPTION).
And finally, when generic_shutdown_super() detects remaining inodes on a
system without CONFIG_BUG_ON_DATA_CORRUPTION, it would be nice if later
accesses to a busy inode would at least crash somewhat cleanly rather than
walking through freed memory.

To address all three, use CHECK_DATA_CORRUPTION() when kernel bugs are
detected.

Signed-off-by: Jann Horn <jannh@google.com>
Reviewed-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/open.c | 5 +++--
fs/super.c | 21 +++++++++++++++++----
include/linux/poison.h | 3 +++
3 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/fs/open.c b/fs/open.c
index a81319b6177f6..7853deb6fcf47 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -1411,8 +1411,9 @@ int filp_close(struct file *filp, fl_owner_t id)
{
int retval = 0;

- if (!file_count(filp)) {
- printk(KERN_ERR "VFS: Close: file count is 0\n");
+ if (CHECK_DATA_CORRUPTION(file_count(filp) == 0,
+ "VFS: Close: file count is 0 (f_op=%ps)",
+ filp->f_op)) {
return 0;
}

diff --git a/fs/super.c b/fs/super.c
index 8d39e4f11cfa3..4f8a626a35cd9 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -491,10 +491,23 @@ void generic_shutdown_super(struct super_block *sb)
if (sop->put_super)
sop->put_super(sb);

- if (!list_empty(&sb->s_inodes)) {
- printk("VFS: Busy inodes after unmount of %s. "
- "Self-destruct in 5 seconds. Have a nice day...\n",
- sb->s_id);
+ if (CHECK_DATA_CORRUPTION(!list_empty(&sb->s_inodes),
+ "VFS: Busy inodes after unmount of %s (%s)",
+ sb->s_id, sb->s_type->name)) {
+ /*
+ * Adding a proper bailout path here would be hard, but
+ * we can at least make it more likely that a later
+ * iput_final() or such crashes cleanly.
+ */
+ struct inode *inode;
+
+ spin_lock(&sb->s_inode_list_lock);
+ list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
+ inode->i_op = VFS_PTR_POISON;
+ inode->i_sb = VFS_PTR_POISON;
+ inode->i_mapping = VFS_PTR_POISON;
+ }
+ spin_unlock(&sb->s_inode_list_lock);
}
}
spin_lock(&sb_lock);
diff --git a/include/linux/poison.h b/include/linux/poison.h
index 2d3249eb0e62d..0e8a1f2ceb2f1 100644
--- a/include/linux/poison.h
+++ b/include/linux/poison.h
@@ -84,4 +84,7 @@
/********** kernel/bpf/ **********/
#define BPF_PTR_POISON ((void *)(0xeB9FUL + POISON_POINTER_DELTA))

+/********** VFS **********/
+#define VFS_PTR_POISON ((void *)(0xF5 + POISON_POINTER_DELTA))
+
#endif
--
2.39.0