Re: [PATCH] pinctrl: avoid unsafe code pattern in find_pinctrl()

[Andy Shevchenko]

On Mon, Sep 25, 2023 at 03:30:53PM +0200, Linus Walleij wrote:
> On Wed, Sep 20, 2023 at 8:09 PM Dmitry Torokhov
> <dmitry.torokhov@xxxxxxxxx> wrote:
> 
> > The code in find_pinctrl() takes a mutex and traverses a list of pinctrl
> > structures. Later the caller bumps up reference count on the found
> > structure. Such pattern is not safe as pinctrl that was found may get
> > deleted before the caller gets around to increasing the reference count.
> >
> > Fix this by taking the reference count in find_pinctrl(), while it still
> > holds the mutex.
> >
> > Signed-off-by: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
> 
> After some thinking, applied for fixes and tagged for stable as
> it is a very real problem that can cause random crashes under
> the right circumstances.

Follow the strange and weird bisection [1] this one at least confirmed to be
the culprit by reverting the only one from the v6.6-rc6 based branch.

Long story short, after this commit my user space setup (minimal Buildroot + Busybox)
has become broken in a sense of MMC enumeration. My all scripts were pointed to
mmcblk0 which becomes out of a sudden mmcblk1!

git bisect start
# status: waiting for both good and bad commits
# bad: [58720809f52779dc0f08e53e54b014209d13eebb] Linux 6.6-rc6
git bisect bad 58720809f52779dc0f08e53e54b014209d13eebb
# status: waiting for good commit(s), bad commit known
# good: [2dde18cd1d8fac735875f2e4987f11817cc0bc2c] Linux 6.5
git bisect good 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
# good: [47ca50600efcf994adb62a9a4e75c77d91bd0781] Merge tag 'soc-defconfig-6.6' of git://git.kernel.org/pub/scm/linux/kernel/git/soc/soc
git bisect good 47ca50600efcf994adb62a9a4e75c77d91bd0781
# good: [b89b029377c8c441649c7a6be908386e74ea9420] Merge tag 'scsi-misc' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi
git bisect good b89b029377c8c441649c7a6be908386e74ea9420
# good: [2a5a4326e58339a26cd1510259e7310b8c0980ff] Merge tag 'scsi-misc' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi
git bisect good 2a5a4326e58339a26cd1510259e7310b8c0980ff
# good: [85eba5f1759f9eb89273225027254ced57bd18a2] Merge tag 'mm-hotfixes-stable-2023-09-23-10-31' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
git bisect good 85eba5f1759f9eb89273225027254ced57bd18a2
# good: [b78b18fb8ee19f7a05f20c3abc865b3bfe182884] Merge tag 'erofs-for-6.6-rc5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs
git bisect good b78b18fb8ee19f7a05f20c3abc865b3bfe182884
# bad: [9a5a14948574ee09f339990cab69b4ab997d2f7d] Merge tag 'soc-fixes-6.6-2' of git://git.kernel.org/pub/scm/linux/kernel/git/soc/soc
git bisect bad 9a5a14948574ee09f339990cab69b4ab997d2f7d
# good: [b9ddbb0cde2adcedda26045cc58f31316a492215] Merge tag 'parisc-for-6.6-rc5' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux
git bisect good b9ddbb0cde2adcedda26045cc58f31316a492215
# good: [b711538a40b794ccc83838fb66990a091c56c101] Merge tag 'hyperv-fixes-signed-20231009' of git://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux
git bisect good b711538a40b794ccc83838fb66990a091c56c101
# good: [bab19d1b21547046b0a38dde948086f6cbcaefaa] Merge tag 'for-linus-2023101101' of git://git.kernel.org/pub/scm/linux/kernel/git/hid/hid
git bisect good bab19d1b21547046b0a38dde948086f6cbcaefaa
# bad: [82a040a8fa9b4f3845eff73a69a9931a59335902] Merge tag 'pinctrl-v6.6-2' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl
git bisect bad 82a040a8fa9b4f3845eff73a69a9931a59335902
# good: [759d1b653f3c7c2249b7fe5f6b218f87a5842822] Merge tag 'for-6.6-rc5-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux
git bisect good 759d1b653f3c7c2249b7fe5f6b218f87a5842822
# bad: [c153a4edff6ab01370fcac8e46f9c89cca1060c2] pinctrl: avoid unsafe code pattern in find_pinctrl()
git bisect bad c153a4edff6ab01370fcac8e46f9c89cca1060c2
# good: [87d315a34133edcb29c4cadbf196ec6c30dfd47b] pinctrl: nuvoton: wpcm450: fix out of bounds write
git bisect good 87d315a34133edcb29c4cadbf196ec6c30dfd47b
# good: [64061b67335e958e6328bcb5bb2b5490d57f3f59] pinctrl: starfive: jh7110: Add system pm ops to save and restore context
git bisect good 64061b67335e958e6328bcb5bb2b5490d57f3f59
# first bad commit: [c153a4edff6ab01370fcac8e46f9c89cca1060c2] pinctrl: avoid unsafe code pattern in find_pinctrl()

[1]: https://lore.kernel.org/r/20230830102434.xnlh66omhs6ninet@quack3

-- 
With Best Regards,
Andy Shevchenko