diff options
| author | Nicolai Stange <nicstange@gmail.com> | 2016-05-05 19:46:19 -0400 |
|---|---|---|
| committer | Theodore Ts'o <tytso@mit.edu> | 2016-05-05 19:46:19 -0400 |
| commit | 935244cd54b86ca46e69bc6604d2adfb1aec2d42 (patch) | |
| tree | 870253dbfdb7e77a71a85ee1357817a7699855b2 /fs | |
| parent | b5cb316cdf3a3f5f6125412b0f6065185240cfdc (diff) | |
| download | linux-935244cd54b86ca46e69bc6604d2adfb1aec2d42.tar.bz2 | |
ext4: silence UBSAN in ext4_mb_init()
Currently, in ext4_mb_init(), there's a loop like the following:
do {
...
offset += 1 << (sb->s_blocksize_bits - i);
i++;
} while (i <= sb->s_blocksize_bits + 1);
Note that the updated offset is used in the loop's next iteration only.
However, at the last iteration, that is at i == sb->s_blocksize_bits + 1,
the shift count becomes equal to (unsigned)-1 > 31 (c.f. C99 6.5.7(3))
and UBSAN reports
UBSAN: Undefined behaviour in fs/ext4/mballoc.c:2621:15
shift exponent 4294967295 is too large for 32-bit type 'int'
[...]
Call Trace:
[<ffffffff818c4d25>] dump_stack+0xbc/0x117
[<ffffffff818c4c69>] ? _atomic_dec_and_lock+0x169/0x169
[<ffffffff819411ab>] ubsan_epilogue+0xd/0x4e
[<ffffffff81941cac>] __ubsan_handle_shift_out_of_bounds+0x1fb/0x254
[<ffffffff81941ab1>] ? __ubsan_handle_load_invalid_value+0x158/0x158
[<ffffffff814b6dc1>] ? kmem_cache_alloc+0x101/0x390
[<ffffffff816fc13b>] ? ext4_mb_init+0x13b/0xfd0
[<ffffffff814293c7>] ? create_cache+0x57/0x1f0
[<ffffffff8142948a>] ? create_cache+0x11a/0x1f0
[<ffffffff821c2168>] ? mutex_lock+0x38/0x60
[<ffffffff821c23ab>] ? mutex_unlock+0x1b/0x50
[<ffffffff814c26ab>] ? put_online_mems+0x5b/0xc0
[<ffffffff81429677>] ? kmem_cache_create+0x117/0x2c0
[<ffffffff816fcc49>] ext4_mb_init+0xc49/0xfd0
[...]
Observe that the mentioned shift exponent, 4294967295, equals (unsigned)-1.
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 offset is never used again.
Silence UBSAN by introducing another variable, offset_incr, holding the
next increment to apply to offset 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>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/ext4/mballoc.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index 49e444b51a0c..c1ab3ec30423 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -2585,7 +2585,7 @@ int ext4_mb_init(struct super_block *sb) { struct ext4_sb_info *sbi = EXT4_SB(sb); unsigned i, j; - unsigned offset; + unsigned offset, offset_incr; unsigned max; int ret; @@ -2614,11 +2614,13 @@ int ext4_mb_init(struct super_block *sb) i = 1; offset = 0; + offset_incr = 1 << (sb->s_blocksize_bits - 1); max = sb->s_blocksize << 2; do { sbi->s_mb_offsets[i] = offset; sbi->s_mb_maxs[i] = max; - offset += 1 << (sb->s_blocksize_bits - i); + offset += offset_incr; + offset_incr = offset_incr >> 1; max = max >> 1; i++; } while (i <= sb->s_blocksize_bits + 1); |