'ac->ac_2order' is a user-controlled value used to index into 'grp->bb_counters' and based on the value at that index, 'ac->ac_found' is written to. Clamp the value right after the bounds check to avoid a speculative out-of-bounds read of 'grp->bb_counters'.
This also protects the access of the s_mb_offsets and s_mb_maxs arrays inside mb_find_buddy().
These gadgets were discovered 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)
Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Jeremy Cline jcline@redhat.com --- fs/ext4/mballoc.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index f7ab34088162..c0866007a949 100644 --- 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>
@@ -1893,6 +1894,7 @@ void ext4_mb_simple_scan_group(struct ext4_allocation_context *ac,
BUG_ON(ac->ac_2order <= 0); for (i = ac->ac_2order; i <= sb->s_blocksize_bits + 1; i++) { + i = array_index_nospec(i, sb->s_blocksize_bits + 2); if (grp->bb_counters[i] == 0) continue;