4.18-stable review patch. If anyone has any objections, please let me know.
------------------
From: Jeremy Cline <jcl...@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 <jpoim...@redhat.com>
Signed-off-by: Jeremy Cline <jcl...@redhat.com>
Signed-off-by: Theodore Ts'o <ty...@mit.edu>
Cc: sta...@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
fs/ext4/mballoc.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -14,6 +14,7 @@
#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>
@@ -2140,7 +2141,8 @@ 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 */
