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

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxx>]

On Tue, Oct 17, 2023 at 05:08:05PM +0300, Andy Shevchenko wrote:
> 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!

`dmesg` after revert:

[   36.439057] mmc0: SDHCI controller on PCI [0000:00:01.0] using ADMA
[   36.450924] mmc2: SDHCI controller on PCI [0000:00:01.3] using ADMA
[   36.459355] mmc1: SDHCI controller on PCI [0000:00:01.2] using ADMA
[   36.706399] mmc0: new DDR MMC card at address 0001
[   37.058972] mmc2: new ultra high speed DDR50 SDIO card at address 0001
[   37.278977] mmcblk0: mmc0:0001 H4G1d 3.64 GiB
[   37.297300]  mmcblk0: p1 p2 p3 p4 p5 p6 p7 p8 p9 p10

and before:

[   36.436704] mmc2: SDHCI controller on PCI [0000:00:01.3] using ADMA
[   36.436720] mmc1: SDHCI controller on PCI [0000:00:01.0] using ADMA
[   36.463685] mmc0: SDHCI controller on PCI [0000:00:01.2] using ADMA
[   36.720627] mmc1: new DDR MMC card at address 0001
[   37.068181] mmc2: new ultra high speed DDR50 SDIO card at address 0001
[   37.279998] mmcblk1: mmc1:0001 H4G1d 3.64 GiB
[   37.302670]  mmcblk1: p1 p2 p3 p4 p5 p6 p7 p8 p9 p10

Reproducibility 100%.

> 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