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authorJeremy Cline <jcline@redhat.com>2018-08-02 00:03:40 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-08-24 13:27:00 +0200
commita89f83823b97b6da1ecf7a51184b28822e78cc07 (patch)
treefe1d851c41e5f552cdff77cd1177ca5e3b9baf86
parent1186a6ea75df00ec27b9cf2c5d0a5e4298739301 (diff)
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 <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>
-rw-r--r--fs/ext4/mballoc.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 75f79ff29ce0..828b4c080c38 100644
--- 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_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 */