| Message ID | 20240503201620.work.651-kees@kernel.org (mailing list archive) |
|---|---|
| State | Mainlined |
| Commit | f6bdc7865ef4a7a4393c90a550c728231ebc853e |
| Headers | show |
| Series | fs: WARN when f_count resurrection is attempted | expand |
On Fri, 03 May 2024 13:16:25 -0700, Kees Cook wrote: > It should never happen that get_file() is called on a file with > f_count equal to zero. If this happens, a use-after-free condition > has happened[1], and we need to attempt a best-effort reporting of > the situation to help find the root cause more easily. Additionally, > this serves as a data corruption indicator that system owners using > warn_limit or panic_on_warn would like to have detected. > > [...] Applied to the vfs.misc branch of the vfs/vfs.git tree. Patches in the vfs.misc branch should appear in linux-next soon. Please report any outstanding bugs that were missed during review in a new review to the original patch series allowing us to drop it. It's encouraged to provide Acked-bys and Reviewed-bys even though the patch has now been applied. If possible patch trailers will be updated. Note that commit hashes shown below are subject to change due to rebase, trailer updates or similar. If in doubt, please check the listed branch. tree: https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git branch: vfs.misc [1/1] fs: WARN when f_count resurrection is attempted https://git.kernel.org/vfs/vfs/c/f6bdc7865ef4
On Fri, May 03, 2024 at 01:16:25PM -0700, Kees Cook wrote: > It should never happen that get_file() is called on a file with > f_count equal to zero. If this happens, a use-after-free condition > has happened[1], and we need to attempt a best-effort reporting of > the situation to help find the root cause more easily. Additionally, > this serves as a data corruption indicator that system owners using > warn_limit or panic_on_warn would like to have detected. > > Link: https://lore.kernel.org/lkml/7c41cf3c-2a71-4dbb-8f34-0337890906fc@gmail.com/ [1] > Suggested-by: Peter Zijlstra <peterz@infradead.org> > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > Cc: Christian Brauner <brauner@kernel.org> > Cc: Alexander Viro <viro@zeniv.linux.org.uk> > Cc: Jens Axboe <axboe@kernel.dk> > Cc: Jann Horn <jannh@google.com> > Cc: Jan Kara <jack@suse.cz> > Cc: linux-fsdevel@vger.kernel.org > --- > include/linux/fs.h | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/include/linux/fs.h b/include/linux/fs.h > index 00fc429b0af0..fa9ea5390f33 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -1038,7 +1038,8 @@ struct file_handle { > > static inline struct file *get_file(struct file *f) > { > - atomic_long_inc(&f->f_count); > + long prior = atomic_long_fetch_inc_relaxed(&f->f_count); > + WARN_ONCE(!prior, "struct file::f_count incremented from zero; use-after-free condition present!\n"); This reminds me, I should some day try and fix the horrible code-gen for WARN() :/ WARN_ON_*() and friends turn into a single trap instruction, but the WARN() and friends thing turns into a horrible piece of crap for the printk().
diff --git a/include/linux/fs.h b/include/linux/fs.h index 00fc429b0af0..fa9ea5390f33 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1038,7 +1038,8 @@ struct file_handle { static inline struct file *get_file(struct file *f) { - atomic_long_inc(&f->f_count); + long prior = atomic_long_fetch_inc_relaxed(&f->f_count); + WARN_ONCE(!prior, "struct file::f_count incremented from zero; use-after-free condition present!\n"); return f; }
It should never happen that get_file() is called on a file with f_count equal to zero. If this happens, a use-after-free condition has happened[1], and we need to attempt a best-effort reporting of the situation to help find the root cause more easily. Additionally, this serves as a data corruption indicator that system owners using warn_limit or panic_on_warn would like to have detected. Link: https://lore.kernel.org/lkml/7c41cf3c-2a71-4dbb-8f34-0337890906fc@gmail.com/ [1] Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Kees Cook <keescook@chromium.org> --- Cc: Christian Brauner <brauner@kernel.org> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jann Horn <jannh@google.com> Cc: Jan Kara <jack@suse.cz> Cc: linux-fsdevel@vger.kernel.org --- include/linux/fs.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)