Ville Syrjälä
2023-Nov-20 15:12 UTC
[Nouveau] [PATCH V2] drm/modes: Fix divide error in drm_mode_debug_printmodeline
On Mon, Nov 20, 2023 at 10:41:18PM +0800, Edward Adam Davis wrote:> [Syz Log] > divide error: 0000 [#1] PREEMPT SMP KASAN > CPU: 0 PID: 5068 Comm: syz-executor357 Not tainted 6.6.0-syzkaller-16039-gac347a0655db #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023 > RIP: 0010:drm_mode_vrefresh drivers/gpu/drm/drm_modes.c:1303 [inline] > RIP: 0010:drm_mode_debug_printmodeline+0x118/0x4e0 drivers/gpu/drm/drm_modes.c:60 > Code: 00 41 0f b7 07 66 83 f8 02 b9 01 00 00 00 0f 43 c8 0f b7 c1 0f af e8 44 89 f0 48 69 c8 e8 03 00 00 89 e8 d1 e8 48 01 c8 31 d2 <48> f7 f5 49 89 c6 eb 0c e8 fb 07 66 fc eb 05 e8 f4 07 66 fc 48 89 > RSP: 0018:ffffc9000391f8d0 EFLAGS: 00010246 > RAX: 000000000001f400 RBX: ffff888025045000 RCX: 000000000001f400 > RDX: 0000000000000000 RSI: 0000000000008000 RDI: ffff888025045018 > RBP: 0000000000000000 R08: ffffffff8528b9af R09: 0000000000000000 > R10: ffffc9000391f8a0 R11: fffff52000723f17 R12: 0000000000000080 > R13: dffffc0000000000 R14: 0000000000000080 R15: ffff888025045016 > FS: 0000555556932380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00000000005fdeb8 CR3: 000000007fcff000 CR4: 00000000003506f0 > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > Call Trace: > <TASK> > drm_mode_setcrtc+0x83b/0x1880 drivers/gpu/drm/drm_crtc.c:794 > drm_ioctl_kernel+0x362/0x500 drivers/gpu/drm/drm_ioctl.c:792 > drm_ioctl+0x636/0xb00 drivers/gpu/drm/drm_ioctl.c:895 > vfs_ioctl fs/ioctl.c:51 [inline] > __do_sys_ioctl fs/ioctl.c:871 [inline] > __se_sys_ioctl+0xf8/0x170 fs/ioctl.c:857 > do_syscall_x64 arch/x86/entry/common.c:51 [inline] > do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82 > entry_SYSCALL_64_after_hwframe+0x63/0x6b > > [Analysis] > When calculating den in drm_mode_vrefresh(), if the vscan value is too large, > there is a probability of unsigned integer overflow. > > [Fix] > Before multiplying by vscan, first check if their product will overflow. > If overflow occurs, return 0 and exit the subsequent process. > > Reported-and-tested-by: syzbot+2e93e6fb36e6fdc56574 at syzkaller.appspotmail.com > Fixes: ea40d7857d52 ("drm/vkms: fbdev emulation support") > Signed-off-by: Edward Adam Davis <eadavis at qq.com> > --- > drivers/gpu/drm/drm_modes.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletion(-) > > diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c > index ac9a406250c5..60739d861da2 100644 > --- a/drivers/gpu/drm/drm_modes.c > +++ b/drivers/gpu/drm/drm_modes.c > @@ -36,6 +36,7 @@ > #include <linux/list.h> > #include <linux/list_sort.h> > #include <linux/of.h> > +#include <linux/overflow.h> > > #include <video/of_display_timing.h> > #include <video/of_videomode.h> > @@ -1297,8 +1298,10 @@ int drm_mode_vrefresh(const struct drm_display_mode *mode) > num *= 2; > if (mode->flags & DRM_MODE_FLAG_DBLSCAN) > den *= 2; > - if (mode->vscan > 1) > - den *= mode->vscan; > + if (mode->vscan > 1) { > + if (unlikely(check_mul_overflow(den, mode->vscan, &den))) > + return 0; > + }I can't see any driver that actually supports vscan>1. Only nouveau has some code for it, but doesn't look like it does anything sensible. All other drivers for sure should be rejecting vscan>1 outright. Which driver is this? Is there an actual usecase where nouveau needs this (and does it even work?) or could we just rip out the whole thing and reject vscan>1 globally?> > return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den); > } > -- > 2.25.1-- Ville Syrj?l? Intel
Jani Nikula
2023-Nov-21 09:20 UTC
[Nouveau] [PATCH V2] drm/modes: Fix divide error in drm_mode_debug_printmodeline
On Mon, 20 Nov 2023, Ville Syrj?l? <ville.syrjala at linux.intel.com> wrote:> On Mon, Nov 20, 2023 at 10:41:18PM +0800, Edward Adam Davis wrote: >> [Syz Log] >> divide error: 0000 [#1] PREEMPT SMP KASAN >> CPU: 0 PID: 5068 Comm: syz-executor357 Not tainted 6.6.0-syzkaller-16039-gac347a0655db #0 >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023 >> RIP: 0010:drm_mode_vrefresh drivers/gpu/drm/drm_modes.c:1303 [inline] >> RIP: 0010:drm_mode_debug_printmodeline+0x118/0x4e0 drivers/gpu/drm/drm_modes.c:60 >> Code: 00 41 0f b7 07 66 83 f8 02 b9 01 00 00 00 0f 43 c8 0f b7 c1 0f af e8 44 89 f0 48 69 c8 e8 03 00 00 89 e8 d1 e8 48 01 c8 31 d2 <48> f7 f5 49 89 c6 eb 0c e8 fb 07 66 fc eb 05 e8 f4 07 66 fc 48 89 >> RSP: 0018:ffffc9000391f8d0 EFLAGS: 00010246 >> RAX: 000000000001f400 RBX: ffff888025045000 RCX: 000000000001f400 >> RDX: 0000000000000000 RSI: 0000000000008000 RDI: ffff888025045018 >> RBP: 0000000000000000 R08: ffffffff8528b9af R09: 0000000000000000 >> R10: ffffc9000391f8a0 R11: fffff52000723f17 R12: 0000000000000080 >> R13: dffffc0000000000 R14: 0000000000000080 R15: ffff888025045016 >> FS: 0000555556932380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000 >> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> CR2: 00000000005fdeb8 CR3: 000000007fcff000 CR4: 00000000003506f0 >> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 >> Call Trace: >> <TASK> >> drm_mode_setcrtc+0x83b/0x1880 drivers/gpu/drm/drm_crtc.c:794 >> drm_ioctl_kernel+0x362/0x500 drivers/gpu/drm/drm_ioctl.c:792 >> drm_ioctl+0x636/0xb00 drivers/gpu/drm/drm_ioctl.c:895 >> vfs_ioctl fs/ioctl.c:51 [inline] >> __do_sys_ioctl fs/ioctl.c:871 [inline] >> __se_sys_ioctl+0xf8/0x170 fs/ioctl.c:857 >> do_syscall_x64 arch/x86/entry/common.c:51 [inline] >> do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82 >> entry_SYSCALL_64_after_hwframe+0x63/0x6b >> >> [Analysis] >> When calculating den in drm_mode_vrefresh(), if the vscan value is too large, >> there is a probability of unsigned integer overflow. >> >> [Fix] >> Before multiplying by vscan, first check if their product will overflow. >> If overflow occurs, return 0 and exit the subsequent process. >> >> Reported-and-tested-by: syzbot+2e93e6fb36e6fdc56574 at syzkaller.appspotmail.com >> Fixes: ea40d7857d52 ("drm/vkms: fbdev emulation support") >> Signed-off-by: Edward Adam Davis <eadavis at qq.com> >> --- >> drivers/gpu/drm/drm_modes.c | 7 +++++-- >> 1 file changed, 5 insertions(+), 2 deletion(-) >> >> diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c >> index ac9a406250c5..60739d861da2 100644 >> --- a/drivers/gpu/drm/drm_modes.c >> +++ b/drivers/gpu/drm/drm_modes.c >> @@ -36,6 +36,7 @@ >> #include <linux/list.h> >> #include <linux/list_sort.h> >> #include <linux/of.h> >> +#include <linux/overflow.h> >> >> #include <video/of_display_timing.h> >> #include <video/of_videomode.h> >> @@ -1297,8 +1298,10 @@ int drm_mode_vrefresh(const struct drm_display_mode *mode) >> num *= 2; >> if (mode->flags & DRM_MODE_FLAG_DBLSCAN) >> den *= 2; >> - if (mode->vscan > 1) >> - den *= mode->vscan; >> + if (mode->vscan > 1) { >> + if (unlikely(check_mul_overflow(den, mode->vscan, &den))) >> + return 0; >> + } > > I can't see any driver that actually supports vscan>1. Only > nouveau has some code for it, but doesn't look like it does > anything sensible. All other drivers for sure should be > rejecting vscan>1 outright. Which driver is this? > > Is there an actual usecase where nouveau needs this (and does > it even work?) or could we just rip out the whole thing and > reject vscan>1 globally?I thought the whole thing seemed familiar [1]. BR, Jani. [1] https://lore.kernel.org/r/20230802174746.2256-1-astrajoan at yahoo.com> >> >> return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den); >> } >> -- >> 2.25.1-- Jani Nikula, Intel