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authorNicolai Stange <nicstange@gmail.com>2016-05-05 17:38:03 -0400
committerTheodore Ts'o <tytso@mit.edu>2016-05-05 17:38:03 -0400
commitb5cb316cdf3a3f5f6125412b0f6065185240cfdc (patch)
tree73741ce9475852c6dc786ea151f09b9fb1e56783 /fs/ext4/mballoc.c
parent74177f55b70e2f2be770dd28684dd6d17106a4ba (diff)
ext4: address UBSAN warning in mb_find_order_for_block()
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>
Diffstat (limited to 'fs/ext4/mballoc.c')
-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 efa111a7606d..49e444b51a0c 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -1266,6 +1266,7 @@ 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);
@@ -1278,7 +1279,8 @@ 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;