Use get_kernel_nofault() to safely access inode and related structures
(superblock, file_system_type) to avoid crashing when the inode pointer
is invalid. This allows the same pattern as dump_mapping().

Note: The original access method for i_state and i_count is preserved,
as get_kernel_nofault() is unnecessary once the inode structure is
verified accessible.

Signed-off-by: Yuto Ohnuki <ytohnuki@amazon.com>
---
 fs/inode.c | 59 ++++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 46 insertions(+), 13 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index 521383223d8a..259ff49189af 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2984,24 +2984,57 @@ umode_t mode_strip_sgid(struct mnt_idmap *idmap,
 EXPORT_SYMBOL(mode_strip_sgid);
 
 #ifdef CONFIG_DEBUG_VFS
-/*
- * Dump an inode.
- *
- * TODO: add a proper inode dumping routine, this is a stub to get debug off the
- * ground.
+/**
+ * dump_inode - dump an inode.
+ * @inode: inode to dump
+ * @reason: reason for dumping
  *
- * TODO: handle getting to fs type with get_kernel_nofault()?
- * See dump_mapping() above.
+ * If inode is an invalid pointer, we don't want to crash accessing it,
+ * so probe everything depending on it carefully with get_kernel_nofault().
  */
 void dump_inode(struct inode *inode, const char *reason)
 {
-	struct super_block *sb = inode->i_sb;
+	struct super_block *sb;
+	struct file_system_type *s_type;
+	const char *fs_name_ptr;
+	char fs_name[32] = {};
+	umode_t mode;
+	unsigned short opflags;
+	unsigned int flags;
+	unsigned int state;
+	int count;
+
+	pr_warn("%s encountered for inode %px\n", reason, inode);
+
+	if (get_kernel_nofault(sb, &inode->i_sb) ||
+	    get_kernel_nofault(mode, &inode->i_mode) ||
+	    get_kernel_nofault(opflags, &inode->i_opflags) ||
+	    get_kernel_nofault(flags, &inode->i_flags)) {
+		pr_warn("invalid inode:%px\n", inode);
+		return;
+	}
 
-	pr_warn("%s encountered for inode %px\n"
-		"fs %s mode %ho opflags 0x%hx flags 0x%x state 0x%x count %d\n",
-		reason, inode, sb->s_type->name, inode->i_mode, inode->i_opflags,
-		inode->i_flags, inode_state_read_once(inode), atomic_read(&inode->i_count));
-}
+	state = inode_state_read_once(inode);
+	count = atomic_read(&inode->i_count);
 
+	if (!sb) {
+		pr_warn("mode:%ho opflags:0x%x flags:0x%x state:0x%x count:%d\n",
+			mode, opflags, flags, state, count);
+		return;
+	}
+
+	if (get_kernel_nofault(s_type, &sb->s_type) || !s_type ||
+	    get_kernel_nofault(fs_name_ptr, &s_type->name) || !fs_name_ptr) {
+		pr_warn("invalid sb:%px mode:%ho opflags:0x%x flags:0x%x state:0x%x count:%d\n",
+			sb, mode, opflags, flags, state, count);
+		return;
+	}
+
+	if (strncpy_from_kernel_nofault(fs_name, fs_name_ptr, sizeof(fs_name) - 1) < 0)
+		strscpy(fs_name, "<invalid>");
+
+	pr_warn("fs:%s mode:%ho opflags:0x%x flags:0x%x state:0x%x count:%d\n",
+		fs_name, mode, opflags, flags, state, count);
+}
 EXPORT_SYMBOL(dump_inode);
 #endif
-- 
2.50.1




Amazon Web Services EMEA SARL, 38 avenue John F. Kennedy, L-1855 Luxembourg, R.C.S. Luxembourg B186284

Amazon Web Services EMEA SARL, Irish Branch, One Burlington Plaza, Burlington Road, Dublin 4, Ireland, branch registration number 908705

On Thu 01-01-26 16:53:04, Yuto Ohnuki wrote:
> Use get_kernel_nofault() to safely access inode and related structures
> (superblock, file_system_type) to avoid crashing when the inode pointer
> is invalid. This allows the same pattern as dump_mapping().
> 
> Note: The original access method for i_state and i_count is preserved,
> as get_kernel_nofault() is unnecessary once the inode structure is
> verified accessible.
> 
> Signed-off-by: Yuto Ohnuki <ytohnuki@amazon.com>

Very nice, thanks! Just one nit below:

> +	state = inode_state_read_once(inode);
> +	count = atomic_read(&inode->i_count);
>  
> +	if (!sb) {
> +		pr_warn("mode:%ho opflags:0x%x flags:0x%x state:0x%x count:%d\n",
> +			mode, opflags, flags, state, count);
> +		return;
> +	}

I'd merge this variant with the variant below because NULL inode->i_sb is
invalid as well and I think it's better to print that sb is invalid
explicitely instead of just not printing sb info. Otherwise feel free to
add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> +
> +	if (get_kernel_nofault(s_type, &sb->s_type) || !s_type ||
> +	    get_kernel_nofault(fs_name_ptr, &s_type->name) || !fs_name_ptr) {
> +		pr_warn("invalid sb:%px mode:%ho opflags:0x%x flags:0x%x state:0x%x count:%d\n",
> +			sb, mode, opflags, flags, state, count);
> +		return;
> +	}
> +
> +	if (strncpy_from_kernel_nofault(fs_name, fs_name_ptr, sizeof(fs_name) - 1) < 0)
> +		strscpy(fs_name, "<invalid>");
> +
> +	pr_warn("fs:%s mode:%ho opflags:0x%x flags:0x%x state:0x%x count:%d\n",
> +		fs_name, mode, opflags, flags, state, count);
> +}
>  EXPORT_SYMBOL(dump_inode);
>  #endif
> -- 
> 2.50.1
> 
> 
> 
> 
> Amazon Web Services EMEA SARL, 38 avenue John F. Kennedy, L-1855 Luxembourg, R.C.S. Luxembourg B186284
> 
> Amazon Web Services EMEA SARL, Irish Branch, One Burlington Plaza, Burlington Road, Dublin 4, Ireland, branch registration number 908705
> 
> 
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

> I'd merge this variant with the variant below because NULL inode->i_sb is
> invalid as well and I think it's better to print that sb is invalid
> explicitely instead of just not printing sb info. Otherwise feel free to
> add:

> Reviewed-by: Jan Kara <jack@suse.cz>

Thank you for reviewing!
Sure, I'll resend v2 with this fix.
Thanks again for the feedback.



Amazon Web Services EMEA SARL, 38 avenue John F. Kennedy, L-1855 Luxembourg, R.C.S. Luxembourg B186284

Amazon Web Services EMEA SARL, Irish Branch, One Burlington Plaza, Burlington Road, Dublin 4, Ireland, branch registration number 908705