From 4bc32484df6a3bdc173301adff0c2fdc66667a40 Mon Sep 17 00:00:00 2001 From: Jeremy Cline Date: Thu, 2 Aug 2018 00:03:40 -0400 Subject: [PATCH] ext4: fix spectre gadget in ext4_mb_regular_allocator() 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 Signed-off-by: Jeremy Cline Signed-off-by: Theodore Ts'o Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman --- fs/ext4/mballoc.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index 048c586d9a8b..1792999eec91 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -26,6 +26,7 @@ #include #include #include +#include #include #include @@ -2152,7 +2153,8 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac) * 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 */ -- 2.20.1