diff options
| author | Nicolai Stange <nicstange@gmail.com> | 2016-05-05 17:38:03 -0400 |
|---|---|---|
| committer | Sasha Levin <sasha.levin@oracle.com> | 2016-06-03 19:15:48 -0400 |
| commit | 76caa7178c24de91cdb2ed0033650c623ad580e3 (patch) | |
| tree | 6b10f27f20f3d0beb7cfe6f70941aee8ac6a994d /fs | |
| parent | f245ed015ed94730b9a9fea17029d7d79fa88dd7 (diff) | |
ext4: address UBSAN warning in mb_find_order_for_block()
[ Upstream commit b5cb316cdf3a3f5f6125412b0f6065185240cfdc ]
Currently, in mb_find_order_for_block(), there's a loop like the following:
while (order <= e4b->bd_blkbits + 1) {
...
bb += 1 << (e4b->bd_blkbits - order);
}
Note that the updated bb is used in the loop's next iteration only.
However, at the last iteration, that is at order == e4b->bd_blkbits + 1,
the shift count becomes negative (c.f. C99 6.5.7(3)) and UBSAN reports
UBSAN: Undefined behaviour in fs/ext4/mballoc.c:1281:11
shift exponent -1 is negative
[...]
Call Trace:
[<ffffffff818c4d35>] dump_stack+0xbc/0x117
[<ffffffff818c4c79>] ? _atomic_dec_and_lock+0x169/0x169
[<ffffffff819411bb>] ubsan_epilogue+0xd/0x4e
[<ffffffff81941cbc>] __ubsan_handle_shift_out_of_bounds+0x1fb/0x254
[<ffffffff81941ac1>] ? __ubsan_handle_load_invalid_value+0x158/0x158
[<ffffffff816e93a0>] ? ext4_mb_generate_from_pa+0x590/0x590
[<ffffffff816502c8>] ? ext4_read_block_bitmap_nowait+0x598/0xe80
[<ffffffff816e7b7e>] mb_find_order_for_block+0x1ce/0x240
[...]
Unless compilers start to do some fancy transformations (which at least
GCC 6.0.0 doesn't currently do), the issue is of cosmetic nature only: the
such calculated value of bb is never used again.
Silence UBSAN by introducing another variable, bb_incr, holding the next
increment to apply to bb and adjust that one by right shifting it by one
position per loop iteration.
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=114701
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=112161
Cc: stable@vger.kernel.org
Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/ext4/mballoc.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index 41260489d3bc..900500c3370c 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -1248,6 +1248,7 @@ static void ext4_mb_unload_buddy(struct ext4_buddy *e4b) static int mb_find_order_for_block(struct ext4_buddy *e4b, int block) { int order = 1; + int bb_incr = 1 << (e4b->bd_blkbits - 1); void *bb; BUG_ON(e4b->bd_bitmap == e4b->bd_buddy); @@ -1260,7 +1261,8 @@ static int mb_find_order_for_block(struct ext4_buddy *e4b, int block) /* this block is part of buddy of order 'order' */ return order; } - bb += 1 << (e4b->bd_blkbits - order); + bb += bb_incr; + bb_incr >>= 1; order++; } return 0; |