| From 1a5d5e5d51e75a5bca67dadbcea8c841934b7b85 Mon Sep 17 00:00:00 2001 |
| From: Jeremy Cline <jcline@redhat.com> |
| Date: Thu, 2 Aug 2018 00:03:40 -0400 |
| Subject: ext4: fix spectre gadget in ext4_mb_regular_allocator() |
| |
| From: Jeremy Cline <jcline@redhat.com> |
| |
| commit 1a5d5e5d51e75a5bca67dadbcea8c841934b7b85 upstream. |
| |
| 'ac->ac_g_ex.fe_len' is a user-controlled value which is used in the |
| derivation of 'ac->ac_2order'. 'ac->ac_2order', in turn, is used to |
| index arrays which makes it a potential spectre gadget. Fix this by |
| sanitizing the value assigned to 'ac->ac2_order'. This covers the |
| following accesses found with the help of smatch: |
| |
| * fs/ext4/mballoc.c:1896 ext4_mb_simple_scan_group() warn: potential |
| spectre issue 'grp->bb_counters' [w] (local cap) |
| |
| * fs/ext4/mballoc.c:445 mb_find_buddy() warn: potential spectre issue |
| 'EXT4_SB(e4b->bd_sb)->s_mb_offsets' [r] (local cap) |
| |
| * fs/ext4/mballoc.c:446 mb_find_buddy() warn: potential spectre issue |
| 'EXT4_SB(e4b->bd_sb)->s_mb_maxs' [r] (local cap) |
| |
| Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com> |
| Signed-off-by: Jeremy Cline <jcline@redhat.com> |
| Signed-off-by: Theodore Ts'o <tytso@mit.edu> |
| Cc: stable@vger.kernel.org |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| fs/ext4/mballoc.c | 4 +++- |
| 1 file changed, 3 insertions(+), 1 deletion(-) |
| |
| --- a/fs/ext4/mballoc.c |
| +++ b/fs/ext4/mballoc.c |
| @@ -26,6 +26,7 @@ |
| #include <linux/log2.h> |
| #include <linux/module.h> |
| #include <linux/slab.h> |
| +#include <linux/nospec.h> |
| #include <linux/backing-dev.h> |
| #include <trace/events/ext4.h> |
| |
| @@ -2144,7 +2145,8 @@ ext4_mb_regular_allocator(struct ext4_al |
| * This should tell if fe_len is exactly power of 2 |
| */ |
| if ((ac->ac_g_ex.fe_len & (~(1 << (i - 1)))) == 0) |
| - ac->ac_2order = i - 1; |
| + ac->ac_2order = array_index_nospec(i - 1, |
| + sb->s_blocksize_bits + 2); |
| } |
| |
| /* if stream allocation is enabled, use global goal */ |
