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SubjectRe: [BUG]Missing i_sb NULL pointer check in destroy_inode()
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On Tue, 2003-11-25 at 00:36, Christoph Hellwig wrote:
> On Mon, Nov 24, 2003 at 11:00:38AM -0800, Mingming Cao wrote:
> > Hello, Andrew, Marcelo,
> >
> > destroy_inode() dereferences inode->i_sb without checking if it is NULL.
> > This is inconsistent with its caller: iput() and clear_inode(), both of
> > which check inode->i_sb before dereferencing it. Since iput() calls
> > destroy_inode() after calling file system's .clear_inode method(via
> > clear_inode()), some file systems might choose to clear the i_sb in the
> > .clear_inode super block operation. This results in a crash in
> > destroy_inode().
> >
> > This issue exists in both 2.6, 2.4 and 2.4 kernel. A simple fix against
> > 2.6.0-test9 is included below. 2.4 based fix should be very similar to
> > this one. Please take a look and consider include it.
>
> inode->i_sb can't be NULL. We should remove all those checks.
>
Sorry I can not agree with this. Maybe the inode->i_sb should not be
NULL, but the kernel still allows the file system to do so. In fact
JFS's diReadSpecial() function clears the inode->i_sb to NULL before
calling iput().

Acutally iput() in 2.6 is missing the check too.(in 2.4 the check is
there). Here is the the incremental fix for 2.6 only:

diff -urNp linux-2.6.0-test10/fs/inode.c a/fs/inode.c
--- linux-2.6.0-test10/fs/inode.c 2003-11-23 17:33:24.000000000 -0800
+++ a/fs/inode.c 2003-11-26 13:59:34.000000000 -0800
@@ -1084,13 +1084,13 @@ static inline void iput_final(struct ino
void iput(struct inode *inode)
{
if (inode) {
- struct super_operations *op = inode->i_sb->s_op;
-
+ struct super_block *sb = inode->i_sb;
+
if (inode->i_state == I_CLEAR)
BUG();

- if (op && op->put_inode)
- op->put_inode(inode);
+ if (sb && sb->op && sb->op->put_inode)
+ sb->op->put_inode(inode);

if (atomic_dec_and_lock(&inode->i_count, &inode_lock))
iput_final(inode);



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