Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933196AbcDTJgn (ORCPT ); Wed, 20 Apr 2016 05:36:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52567 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932079AbcDTJgk (ORCPT ); Wed, 20 Apr 2016 05:36:40 -0400 Subject: Re: [PATCH] lib: Always NUL terminate ucs2_as_utf8 To: Chris Wilson , Peter Jones References: <1461141427-16361-1-git-send-email-chris@chris-wilson.co.uk> Cc: intel-gfx@lists.freedesktop.org, Matt Fleming , Jason Andryuk , Matthew Garrett , linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org From: Laszlo Ersek Message-ID: <57174DA5.6030602@redhat.com> Date: Wed, 20 Apr 2016 11:36:37 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.2 MIME-Version: 1.0 In-Reply-To: <1461141427-16361-1-git-send-email-chris@chris-wilson.co.uk> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5765 Lines: 155 On 04/20/16 10:37, Chris Wilson wrote: > If the caller, in this case efivarfs_callback(), only provides sufficent > room for the expanded utf8 and not enough to include the terminating NUL > byte, that NUL byte is skipped. How does that occur? In efivarfs_callback() [fs/efivarfs/super.c], we have len = ucs2_utf8size(entry->var.VariableName); /* name, plus '-', plus GUID, plus NUL*/ name = kmalloc(len + 1 + EFI_VARIABLE_GUID_LEN + 1, GFP_KERNEL); if (!name) goto fail; ucs2_as_utf8(name, entry->var.VariableName, len); Instead, I think the following might be happening (note that RIP points into efivar_variable_is_removable(), and I guess variable_matches() (which is static) is inlined): efivarfs_callback() [fs/efivarfs/super.c] efivar_variable_is_removable() [drivers/firmware/efi/vars.c] variable_matches() [drivers/firmware/efi/vars.c] The bug seems to be in variable_matches(), which doesn't consider the "len" parameter early enough. Namely, consider that we have the following input: - var_name: "a" - len: 1 - match_name "ab" In the first iteration of the loop (i.e., *match == 0): - c = 'a' - u = 'a' - *match gets incremented to 1. In the second iteration of the loop (i.e., *match == 1): - c = 'b' - u = (that is, undefined behavior), because (*match == len). This seems to be consistent with the error message "Caught 8-bit read from uninitialized memory": namely, the array allocated for "name" in efivarfs_callback() is indeed not pre-zeroed, and the ucs2_as_utf8() function does not populate name[len] -- correctly, I would say. So, I think the function that needs a fix is variable_matches(). (I don't disagree though that it could be useful to audit all ucs2_as_utf8() calls.) Thanks Laszlo > When the caller then interprets it as a > string, it may then read from past its allocated memory: > > [ 170.605647] WARNING: kmemcheck: Caught 8-bit read from uninitialized memory (ffff8804079ae786) > [ 170.605677] 436f6e4f757400004c44322d35363062663538612d316530642d346437652d39 > [ 170.606037] i i i i i i u u u u u u u u u u u u u u u u u u u u u u u u u u > [ 170.606236] ^ > [ 170.606243] RIP: 0010:[] [] efivar_variable_is_removable+0xaf/0xf0 > [ 170.606346] RSP: 0018:ffff880408e73c20 EFLAGS: 00010206 > [ 170.606352] RAX: 0000000000000000 RBX: 0000000000000006 RCX: 0000000000000006 > [ 170.606359] RDX: 0000000000000000 RSI: 0000000000000074 RDI: ffff880408e73c30 > [ 170.606365] RBP: ffff880408e73c80 R08: 0000000000000006 R09: 000000000000008c > [ 170.606371] R10: 0000000000000006 R11: 0000000000000000 R12: ffffffff8166ed20 > [ 170.606378] R13: 11d293ca8be4df61 R14: ffffffff81773834 R15: ffff8804079ae780 > [ 170.606385] FS: 0000000000000000(0000) GS:ffff88041ca00000(0000) knlGS:0000000000000000 > [ 170.606392] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 170.606399] CR2: ffff880409cbe4c0 CR3: 00000004085fd000 CR4: 00000000001406f0 > [ 170.606405] [] efivarfs_callback+0xf8/0x275 > [ 170.606418] [] efivar_init+0x248/0x2e0 > [ 170.606440] [] efivarfs_fill_super+0xb4/0xf0 > [ 170.606452] [] mount_single+0x87/0xb0 > [ 170.606463] [] efivarfs_mount+0x13/0x20 > [ 170.606475] [] mount_fs+0x10/0x90 > [ 170.606497] [] vfs_kern_mount+0x62/0x100 > [ 170.606508] [] do_mount+0x1e0/0xcd0 > [ 170.606519] [] SyS_mount+0x8f/0xd0 > [ 170.606530] [] entry_SYSCALL_64_fastpath+0x17/0x93 > [ 170.606542] [] 0xffffffffffffffff > > Cc: Matt Fleming > Cc: Jason Andryuk > Cc: Matthew Garrett > Cc: Laszlo Ersek > Cc: Peter Jones > Cc: linux-efi@vger.kernel.org > Cc: linux-kernel@vger.kernel.org > --- > drivers/firmware/efi/vars.c | 2 +- > lib/ucs2_string.c | 15 ++++++++++----- > 2 files changed, 11 insertions(+), 6 deletions(-) > > diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c > index 0ac594c0a234..8dd503bac35d 100644 > --- a/drivers/firmware/efi/vars.c > +++ b/drivers/firmware/efi/vars.c > @@ -166,7 +166,7 @@ validate_ascii_string(efi_char16_t *var_name, int match, u8 *buffer, > > struct variable_validate { > efi_guid_t vendor; > - char *name; > + const char *name; > bool (*validate)(efi_char16_t *var_name, int match, u8 *data, > unsigned long len); > }; > diff --git a/lib/ucs2_string.c b/lib/ucs2_string.c > index f0b323abb4c6..fb8d03966656 100644 > --- a/lib/ucs2_string.c > +++ b/lib/ucs2_string.c > @@ -85,29 +85,34 @@ ucs2_as_utf8(u8 *dest, const ucs2_char_t *src, unsigned long maxlength) > unsigned long j = 0; > unsigned long limit = ucs2_strnlen(src, maxlength); > > - for (i = 0; maxlength && i < limit; i++) { > + if (maxlength == 0) > + return 0; > + > + for (i = 0; i < limit; i++) { > u16 c = src[i]; > > if (c >= 0x800) { > - if (maxlength < 3) > + if (maxlength <= 3) > break; > maxlength -= 3; > dest[j++] = 0xe0 | (c & 0xf000) >> 12; > dest[j++] = 0x80 | (c & 0x0fc0) >> 6; > dest[j++] = 0x80 | (c & 0x003f); > } else if (c >= 0x80) { > - if (maxlength < 2) > + if (maxlength <= 2) > break; > maxlength -= 2; > dest[j++] = 0xc0 | (c & 0x7c0) >> 6; > dest[j++] = 0x80 | (c & 0x03f); > } else { > + if (maxlength <= 1) > + break; > maxlength -= 1; > dest[j++] = c & 0x7f; > } > } > - if (maxlength) > - dest[j] = '\0'; > + dest[j] = '\0'; > + > return j; > } > EXPORT_SYMBOL(ucs2_as_utf8); >