Messages in this thread | | | Date | Fri, 10 Oct 2008 12:17:53 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] drm: fix leak of uninitialized data to userspace |
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* Vegard Nossum <vegardno@ifi.uio.no> wrote:
> >From f2e1569413900fa3ce5dad571e1a24d31307ab75 Mon Sep 17 00:00:00 2001 > From: Vegard Nossum <vegardno@thuin.ifi.uio.no> > Date: Fri, 10 Oct 2008 11:50:57 +0200 > Subject: [PATCH] drm: fix leak of uninitialized data to userspace > > On Fri, Oct 10, 2008 at 10:54 AM, Sitsofe Wheeler <sitsofe@yahoo.com> wrote: > > > > [ 175.375036] WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (f65d2294) > > [ 175.375049] 7063693a303030303a30303a30322e3000a76c080800000000a76c080e000000 > > [ 175.375096] i i i i i i i i i i i i i i i i i u u u u u u u u u u u u u u u > > [ 175.375137] ^ > > [ 175.375142] > > [ 175.375148] Pid: 2288, comm: Xorg Not tainted (2.6.27-tipskw-00069-g37cb0b7-dirty #81) 900 > > [ 175.375155] EIP: 0060:[<c020d283>] EFLAGS: 00003246 CPU: 0 > > [ 175.375169] EIP is at __copy_to_user_ll+0x43/0x60 > > [ 175.375174] EAX: 00000000 EBX: 00000028 ECX: 00000005 EDX: f65d2280 > > [ 175.375180] ESI: f65d2294 EDI: 086cb6b4 EBP: f631bef4 ESP: c055bd68 > > [ 175.375186] DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 0068 > > [ 175.375191] CR0: 8005003b CR2: f67c1c44 CR3: 36368000 CR4: 000006c0 > > [ 175.375197] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000 > > [ 175.375202] DR6: ffff4ff0 DR7: 00000400 > > [ 175.375206] [<c020d6f3>] copy_to_user+0x43/0x60 > > [ 175.375214] [<c028df28>] drm_getunique+0x38/0x50 > > [ 175.375224] [<c028d329>] drm_ioctl+0x1b9/0x2f0 > > [ 175.375231] [<c0188a07>] vfs_ioctl+0x67/0x70 > > [ 175.375239] [<c0188a6c>] do_vfs_ioctl+0x5c/0x270 > > [ 175.375246] [<c0188cbe>] sys_ioctl+0x3e/0x60 > > [ 175.375253] [<c010336d>] sysenter_do_call+0x12/0x35 > > [ 175.375261] [<ffffffff>] 0xffffffff > > The hexdump decodes to: > > vegardno@thuin ~ $ ./a.out 7063693a303030303a30303a30322e3000a76c080800000000a76c080e000000 > pci:0000:00:02.0<0><167>l<8><8><0><0><0><0><167>l<8><14><0><0><0> > > ...so drm_getunique() is trying to copy some uninitialized data to > userspace. The ECX register contains the number of words that are > left to copy -- so there are 5 * 4 = 20 bytes left. The offset of the > first uninitialized byte (counting from the start of the string) is > also 20 (i.e. 0xf65d2294&((1 << 5)-1) == 20). So somebody tried to > copy 40 bytes when the string was only 19 long. > > In drm_set_busid() we have this code: > > dev->unique_len = 40; > dev->unique = drm_alloc(dev->unique_len + 1, DRM_MEM_DRIVER); > ... > len = snprintf(dev->unique, dev->unique_len, "pci:%04x:%02x:%02x.%d", > > ...so it seems that dev->unique is never updated to reflect the > actual length of the string. The remaining bytes (20 in this case) > are random uninitialized bytes that are copied into userspace. > > This patch fixes the problem by setting dev->unique_len after the > snprintf(). > > Completely untested. > > Reported-by: Sitsofe Wheeler <sitsofe@yahoo.com> > Signed-off-by: Vegard Nossum <vegardno@thuin.ifi.uio.no>
i've stuck it into the tip/out-of-tree quick-fixes branch.
Sitsofe, could you please check very latest tip/master with CONFIG_KMEMCHECK=y, does it find any other uninitialized memory access?
Ingo
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