| Message ID | 20240208114411.14604-1-jirislaby@kernel.org (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Headers | show |
| Series | fbcon: always restore the old font data in fbcon_do_set_font() | expand |
On Thu, 8 Feb 2024 at 12:44, Jiri Slaby (SUSE) <jirislaby@kernel.org> wrote: > > Commit a5a923038d70 (fbdev: fbcon: Properly revert changes when > vc_resize() failed) started restoring old font data upon failure (of > vc_resize()). But it performs so only for user fonts. It means that the > "system"/internal fonts are not restored at all. So in result, the very > first call to fbcon_do_set_font() performs no restore at all upon > failing vc_resize(). > > This can be reproduced by Syzkaller to crash the system on the next > invocation of font_get(). It's rather hard to hit the allocation failure > in vc_resize() on the first font_set(), but not impossible. Esp. if > fault injection is used to aid the execution/failure. It was > demonstrated by Sirius: > BUG: unable to handle page fault for address: fffffffffffffff8 > #PF: supervisor read access in kernel mode > #PF: error_code(0x0000) - not-present page > PGD cb7b067 P4D cb7b067 PUD cb7d067 PMD 0 > Oops: 0000 [#1] PREEMPT SMP KASAN > CPU: 1 PID: 8007 Comm: poc Not tainted 6.7.0-g9d1694dc91ce #20 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 > RIP: 0010:fbcon_get_font+0x229/0x800 drivers/video/fbdev/core/fbcon.c:2286 > Call Trace: > <TASK> > con_font_get drivers/tty/vt/vt.c:4558 [inline] > con_font_op+0x1fc/0xf20 drivers/tty/vt/vt.c:4673 > vt_k_ioctl drivers/tty/vt/vt_ioctl.c:474 [inline] > vt_ioctl+0x632/0x2ec0 drivers/tty/vt/vt_ioctl.c:752 > tty_ioctl+0x6f8/0x1570 drivers/tty/tty_io.c:2803 > vfs_ioctl fs/ioctl.c:51 [inline] > ... > > So restore the font data in any case, not only for user fonts. Note the > later 'if' is now protected by 'old_userfont' and not 'old_data' as the > latter is always set now. (And it is supposed to be non-NULL. Otherwise > we would see the bug above again.) > > Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org> > Fixes: a5a923038d70 ("fbdev: fbcon: Properly revert changes when vc_resize() failed") > Cc: Ubisectech Sirius <bugreport@ubisectech.com> > Cc: Daniel Vetter <daniel@ffwll.ch> > Cc: Helge Deller <deller@gmx.de> > Cc: linux-fbdev@vger.kernel.org > Cc: dri-devel@lists.freedesktop.org Reviewing patches to code where assignments in if conditions are still cool is a pain :-/ Merged to drm-misc-fixes with reported/tested-by credit tag for sirius added. Thanks a lot! -Sima > --- > drivers/video/fbdev/core/fbcon.c | 8 +++----- > 1 file changed, 3 insertions(+), 5 deletions(-) > > diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c > index 17a9fc80b4e4..98d0e2dbcd2f 100644 > --- a/drivers/video/fbdev/core/fbcon.c > +++ b/drivers/video/fbdev/core/fbcon.c > @@ -2395,11 +2395,9 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount, > struct fbcon_ops *ops = info->fbcon_par; > struct fbcon_display *p = &fb_display[vc->vc_num]; > int resize, ret, old_userfont, old_width, old_height, old_charcount; > - char *old_data = NULL; > + u8 *old_data = vc->vc_font.data; > > resize = (w != vc->vc_font.width) || (h != vc->vc_font.height); > - if (p->userfont) > - old_data = vc->vc_font.data; > vc->vc_font.data = (void *)(p->fontdata = data); > old_userfont = p->userfont; > if ((p->userfont = userfont)) > @@ -2433,13 +2431,13 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount, > update_screen(vc); > } > > - if (old_data && (--REFCOUNT(old_data) == 0)) > + if (old_userfont && (--REFCOUNT(old_data) == 0)) > kfree(old_data - FONT_EXTRA_WORDS * sizeof(int)); > return 0; > > err_out: > p->fontdata = old_data; > - vc->vc_font.data = (void *)old_data; > + vc->vc_font.data = old_data; > > if (userfont) { > p->userfont = old_userfont; > -- > 2.43.0 >
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c index 17a9fc80b4e4..98d0e2dbcd2f 100644 --- a/drivers/video/fbdev/core/fbcon.c +++ b/drivers/video/fbdev/core/fbcon.c @@ -2395,11 +2395,9 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount, struct fbcon_ops *ops = info->fbcon_par; struct fbcon_display *p = &fb_display[vc->vc_num]; int resize, ret, old_userfont, old_width, old_height, old_charcount; - char *old_data = NULL; + u8 *old_data = vc->vc_font.data; resize = (w != vc->vc_font.width) || (h != vc->vc_font.height); - if (p->userfont) - old_data = vc->vc_font.data; vc->vc_font.data = (void *)(p->fontdata = data); old_userfont = p->userfont; if ((p->userfont = userfont)) @@ -2433,13 +2431,13 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount, update_screen(vc); } - if (old_data && (--REFCOUNT(old_data) == 0)) + if (old_userfont && (--REFCOUNT(old_data) == 0)) kfree(old_data - FONT_EXTRA_WORDS * sizeof(int)); return 0; err_out: p->fontdata = old_data; - vc->vc_font.data = (void *)old_data; + vc->vc_font.data = old_data; if (userfont) { p->userfont = old_userfont;
Commit a5a923038d70 (fbdev: fbcon: Properly revert changes when vc_resize() failed) started restoring old font data upon failure (of vc_resize()). But it performs so only for user fonts. It means that the "system"/internal fonts are not restored at all. So in result, the very first call to fbcon_do_set_font() performs no restore at all upon failing vc_resize(). This can be reproduced by Syzkaller to crash the system on the next invocation of font_get(). It's rather hard to hit the allocation failure in vc_resize() on the first font_set(), but not impossible. Esp. if fault injection is used to aid the execution/failure. It was demonstrated by Sirius: BUG: unable to handle page fault for address: fffffffffffffff8 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD cb7b067 P4D cb7b067 PUD cb7d067 PMD 0 Oops: 0000 [#1] PREEMPT SMP KASAN CPU: 1 PID: 8007 Comm: poc Not tainted 6.7.0-g9d1694dc91ce #20 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 RIP: 0010:fbcon_get_font+0x229/0x800 drivers/video/fbdev/core/fbcon.c:2286 Call Trace: <TASK> con_font_get drivers/tty/vt/vt.c:4558 [inline] con_font_op+0x1fc/0xf20 drivers/tty/vt/vt.c:4673 vt_k_ioctl drivers/tty/vt/vt_ioctl.c:474 [inline] vt_ioctl+0x632/0x2ec0 drivers/tty/vt/vt_ioctl.c:752 tty_ioctl+0x6f8/0x1570 drivers/tty/tty_io.c:2803 vfs_ioctl fs/ioctl.c:51 [inline] ... So restore the font data in any case, not only for user fonts. Note the later 'if' is now protected by 'old_userfont' and not 'old_data' as the latter is always set now. (And it is supposed to be non-NULL. Otherwise we would see the bug above again.) Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org> Fixes: a5a923038d70 ("fbdev: fbcon: Properly revert changes when vc_resize() failed") Cc: Ubisectech Sirius <bugreport@ubisectech.com> Cc: Daniel Vetter <daniel@ffwll.ch> Cc: Helge Deller <deller@gmx.de> Cc: linux-fbdev@vger.kernel.org Cc: dri-devel@lists.freedesktop.org --- drivers/video/fbdev/core/fbcon.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-)