From: Samuel Thibault <samuel.thibault@ens-lyon.org> To: Greg KH <gregkh@linuxfoundation.org> Cc: Daniel Vetter <daniel@ffwll.ch>, Helge Deller <deller@gmx.de>, linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Sanan Hasanov <sanan.hasanov@knights.ucf.edu> Subject: Re: [PATCH] fbcon: Check font dimension limits Date: Sun, 29 Jan 2023 16:13:07 +0100 [thread overview] Message-ID: <20230129151307.o4lsqgmnr2u2k3za@begin> (raw) In-Reply-To: <Y9IvBoAbmh27xl4B@kroah.com> Greg KH, le jeu. 26 janv. 2023 08:43:02 +0100, a ecrit: > On Thu, Jan 26, 2023 at 01:49:12AM +0100, Samuel Thibault wrote: > > blit_x and blit_y are uint32_t, so fbcon currently cannot support fonts > > larger than 32x32. > > "u32" you mean, right? Right :) > > The 32x32 case also needs shifting an unsigned int, to properly set bit > > 31, otherwise we get "UBSAN: shift-out-of-bounds in fbcon_set_font", > > as reported on > > > > http://lore.kernel.org/all/IA1PR07MB98308653E259A6F2CE94A4AFABCE9@IA1PR07MB9830.namprd07.prod.outlook.com > > Odd blank line? Not sure what you mean? I found it easier to read to put a blank line between the text and the references. > > Kernel Branch: 6.2.0-rc5-next-20230124 > > Kernel config: https://drive.google.com/file/d/1F-LszDAizEEH0ZX0HcSR06v5q8FPl2Uv/view?usp=sharing > > Reproducer: https://drive.google.com/file/d/1mP1jcLBY7vWCNM60OMf-ogw-urQRjNrm/view?usp=sharing > > What are all of these lines for? They provide the references that were set in the original report http://lore.kernel.org/all/IA1PR07MB98308653E259A6F2CE94A4AFABCE9@IA1PR07MB9830.namprd07.prod.outlook.com Arguably the "branch" and "config" are not that useful since the bug has been there for more than a dozen years, but notably the "Reproducer" is useful to provide a userland program that triggers the UB. > > Reported-by: Sanan Hasanov <sanan.hasanov@Knights.ucf.edu> > > Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org> > > What commit id does this fix? I though it was there forever, but it seems the check was added in 2007, so I'll add it in next version. > Should it go to stable kernels? Yes. I added stable in Cc of the mail but missed adding it in the text, I will add it. > > Index: linux-6.0/drivers/video/fbdev/core/fbcon.c > > =================================================================== > > --- linux-6.0.orig/drivers/video/fbdev/core/fbcon.c > > +++ linux-6.0/drivers/video/fbdev/core/fbcon.c > > @@ -2489,9 +2489,12 @@ static int fbcon_set_font(struct vc_data > > h > FBCON_SWAP(info->var.rotate, info->var.yres, info->var.xres)) > > return -EINVAL; > > > > + if (font->width > 32 || font->height > 32) > > + return -EINVAL; > > + > > /* Make sure drawing engine can handle the font */ > > - if (!(info->pixmap.blit_x & (1 << (font->width - 1))) || > > - !(info->pixmap.blit_y & (1 << (font->height - 1)))) > > + if (!(info->pixmap.blit_x & (1U << (font->width - 1))) || > > + !(info->pixmap.blit_y & (1U << (font->height - 1)))) > > Are you sure this is still needed with the above check added? If so, > why? What is the difference in the compiled code? As mentioned by Jiri, yes in the 32 case it's needed otherwise it's UB. Samuel
WARNING: multiple messages have this Message-ID (diff)
From: Samuel Thibault <samuel.thibault@ens-lyon.org> To: Greg KH <gregkh@linuxfoundation.org> Cc: linux-fbdev@vger.kernel.org, Sanan Hasanov <sanan.hasanov@knights.ucf.edu>, Helge Deller <deller@gmx.de>, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, stable@vger.kernel.org Subject: Re: [PATCH] fbcon: Check font dimension limits Date: Sun, 29 Jan 2023 16:13:07 +0100 [thread overview] Message-ID: <20230129151307.o4lsqgmnr2u2k3za@begin> (raw) In-Reply-To: <Y9IvBoAbmh27xl4B@kroah.com> Greg KH, le jeu. 26 janv. 2023 08:43:02 +0100, a ecrit: > On Thu, Jan 26, 2023 at 01:49:12AM +0100, Samuel Thibault wrote: > > blit_x and blit_y are uint32_t, so fbcon currently cannot support fonts > > larger than 32x32. > > "u32" you mean, right? Right :) > > The 32x32 case also needs shifting an unsigned int, to properly set bit > > 31, otherwise we get "UBSAN: shift-out-of-bounds in fbcon_set_font", > > as reported on > > > > http://lore.kernel.org/all/IA1PR07MB98308653E259A6F2CE94A4AFABCE9@IA1PR07MB9830.namprd07.prod.outlook.com > > Odd blank line? Not sure what you mean? I found it easier to read to put a blank line between the text and the references. > > Kernel Branch: 6.2.0-rc5-next-20230124 > > Kernel config: https://drive.google.com/file/d/1F-LszDAizEEH0ZX0HcSR06v5q8FPl2Uv/view?usp=sharing > > Reproducer: https://drive.google.com/file/d/1mP1jcLBY7vWCNM60OMf-ogw-urQRjNrm/view?usp=sharing > > What are all of these lines for? They provide the references that were set in the original report http://lore.kernel.org/all/IA1PR07MB98308653E259A6F2CE94A4AFABCE9@IA1PR07MB9830.namprd07.prod.outlook.com Arguably the "branch" and "config" are not that useful since the bug has been there for more than a dozen years, but notably the "Reproducer" is useful to provide a userland program that triggers the UB. > > Reported-by: Sanan Hasanov <sanan.hasanov@Knights.ucf.edu> > > Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org> > > What commit id does this fix? I though it was there forever, but it seems the check was added in 2007, so I'll add it in next version. > Should it go to stable kernels? Yes. I added stable in Cc of the mail but missed adding it in the text, I will add it. > > Index: linux-6.0/drivers/video/fbdev/core/fbcon.c > > =================================================================== > > --- linux-6.0.orig/drivers/video/fbdev/core/fbcon.c > > +++ linux-6.0/drivers/video/fbdev/core/fbcon.c > > @@ -2489,9 +2489,12 @@ static int fbcon_set_font(struct vc_data > > h > FBCON_SWAP(info->var.rotate, info->var.yres, info->var.xres)) > > return -EINVAL; > > > > + if (font->width > 32 || font->height > 32) > > + return -EINVAL; > > + > > /* Make sure drawing engine can handle the font */ > > - if (!(info->pixmap.blit_x & (1 << (font->width - 1))) || > > - !(info->pixmap.blit_y & (1 << (font->height - 1)))) > > + if (!(info->pixmap.blit_x & (1U << (font->width - 1))) || > > + !(info->pixmap.blit_y & (1U << (font->height - 1)))) > > Are you sure this is still needed with the above check added? If so, > why? What is the difference in the compiled code? As mentioned by Jiri, yes in the 32 case it's needed otherwise it's UB. Samuel
next prev parent reply other threads:[~2023-01-29 15:13 UTC|newest] Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <20230126004911.869923511@ens-lyon.org> 2023-01-26 0:49 ` [PATCH] fbcon: Check font dimension limits Samuel Thibault 2023-01-26 0:49 ` Samuel Thibault 2023-01-26 0:51 ` Samuel Thibault 2023-01-26 0:51 ` Samuel Thibault 2023-01-26 7:43 ` Greg KH 2023-01-26 7:43 ` Greg KH 2023-01-26 9:08 ` Jiri Slaby 2023-01-26 9:08 ` Jiri Slaby 2023-01-29 15:13 ` Samuel Thibault [this message] 2023-01-29 15:13 ` Samuel Thibault 2023-01-26 9:02 ` Jiri Slaby 2023-01-26 9:02 ` Jiri Slaby 2023-01-29 15:04 ` Samuel Thibault 2023-01-29 15:04 ` Samuel Thibault 2023-01-28 1:32 ` kernel test robot
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