| Message ID | 20231202212217.243710-3-keescook@chromium.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | pstore: Initial use of cleanup.h | expand |
On Sat, Dec 02, 2023 at 01:22:13PM -0800, Kees Cook wrote:
> Allow __free(iput) markings for easier cleanup on inode allocations.
NAK. That's a bloody awful idea for that particular data type, since
1) ERR_PTR(...) is not uncommon and passing it to iput() is a bug.
2) the common pattern is to have reference-consuming primitives,
with failure exits normally *not* having to do iput() at all.
Please, don't.
On Sat, Dec 02, 2023 at 09:28:46PM +0000, Al Viro wrote: > On Sat, Dec 02, 2023 at 01:22:13PM -0800, Kees Cook wrote: > > Allow __free(iput) markings for easier cleanup on inode allocations. > > NAK. That's a bloody awful idea for that particular data type, since > 1) ERR_PTR(...) is not uncommon and passing it to iput() is a bug. Ah, sounds like instead of "if (_T)", you'd rather see "if (!IS_ERR_OR_NULL(_T))" ? > 2) the common pattern is to have reference-consuming primitives, > with failure exits normally *not* having to do iput() at all. This I'm not following. If I make a call to "new_inode(sb)" that I end up not using, I need to call "iput()" in it... How should this patch be written to avoid the iput() on failure? https://lore.kernel.org/all/20231202212217.243710-4-keescook@chromium.org/ -Kees
On Sat, Dec 02, 2023 at 01:34:32PM -0800, Kees Cook wrote: > On Sat, Dec 02, 2023 at 09:28:46PM +0000, Al Viro wrote: > > On Sat, Dec 02, 2023 at 01:22:13PM -0800, Kees Cook wrote: > > > Allow __free(iput) markings for easier cleanup on inode allocations. > > > > NAK. That's a bloody awful idea for that particular data type, since > > 1) ERR_PTR(...) is not uncommon and passing it to iput() is a bug. > > Ah, sounds like instead of "if (_T)", you'd rather see > "if (!IS_ERR_OR_NULL(_T))" ? No. I would rather *not* see IS_ERR_OR_NULL anywhere, but that's a separate rant. > > 2) the common pattern is to have reference-consuming primitives, > > with failure exits normally *not* having to do iput() at all. > > This I'm not following. If I make a call to "new_inode(sb)" that I end > up not using, I need to call "iput()" in it... > > How should this patch be written to avoid the iput() on failure? > https://lore.kernel.org/all/20231202212217.243710-4-keescook@chromium.org/ I'll poke around and see what I can suggest; said that, one thing I have spotted there on the quick look is that you are exposing hashed dentry associated with your inode before you set its ->i_private. Have an open() hit just after that d_add() and this static int pstore_file_open(struct inode *inode, struct file *file) { struct pstore_private *ps = inode->i_private; struct seq_file *sf; int err; const struct seq_operations *sops = NULL; if (ps->record->type == PSTORE_TYPE_FTRACE) ... with happily oops on you.
On Sat, Dec 02, 2023 at 09:42:12PM +0000, Al Viro wrote: > I'll poke around and see what I can suggest; said that, one thing I have > spotted there on the quick look is that you are exposing hashed dentry associated > with your inode before you set its ->i_private. ... and on the second look, no, you do not do anything of that sort. My apologies...
On Sat, Dec 02, 2023 at 01:34:32PM -0800, Kees Cook wrote: > On Sat, Dec 02, 2023 at 09:28:46PM +0000, Al Viro wrote: > > On Sat, Dec 02, 2023 at 01:22:13PM -0800, Kees Cook wrote: > > > Allow __free(iput) markings for easier cleanup on inode allocations. > > > > NAK. That's a bloody awful idea for that particular data type, since > > 1) ERR_PTR(...) is not uncommon and passing it to iput() is a bug. > > Ah, sounds like instead of "if (_T)", you'd rather see > "if (!IS_ERR_OR_NULL(_T))" ? > > > 2) the common pattern is to have reference-consuming primitives, > > with failure exits normally *not* having to do iput() at all. > > This I'm not following. If I make a call to "new_inode(sb)" that I end > up not using, I need to call "iput()" in it... If we wanted to do this properly then we would need to emulate consume or move semantics like Rust has. So a cleanup function for inodes based on scope for example and then another primitive that transfers/moves ownership of that refcount to the consumer. Usually this is emulate by stuff like TAKE_POINTER() and similar stuff in userspace. But I'm not sure how pleasant it would be to do this cleanly.
diff --git a/include/linux/fs.h b/include/linux/fs.h index 98b7a7a8c42e..7c3eed3dd1bf 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2459,6 +2459,8 @@ extern int current_umask(void); extern void ihold(struct inode * inode); extern void iput(struct inode *); +DEFINE_FREE(iput, struct inode *, if (_T) iput(_T)) + int inode_update_timestamps(struct inode *inode, int flags); int generic_update_time(struct inode *, int);
Allow __free(iput) markings for easier cleanup on inode allocations. Cc: Christian Brauner <brauner@kernel.org> Cc: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Kees Cook <keescook@chromium.org> --- include/linux/fs.h | 2 ++ 1 file changed, 2 insertions(+)