Re: [PATCH v2] fs/ext4: fix integer overflow in s_log_groups_per_flex
From: Jan Kara
Date: Wed Feb 24 2021 - 05:06:44 EST
On Wed 24-02-21 15:58:00, Sabyrzhan Tasbolatov wrote:
>
syzbot found UBSAN: shift-out-of-bounds in ext4_mb_init [1], when
>
1 << sbi->s_es->s_log_groups_per_flex is bigger than UINT_MAX,
>
where sbi->s_mb_prefetch is unsigned integer type.
>
>
32 is the maximum allowed power of s_log_groups_per_flex. Following if
>
check will also trigger UBSAN shift-out-of-bound:
>
>
if (1 << sbi->s_es->s_log_groups_per_flex >= UINT_MAX) {
>
>
So I'm checking it against the raw number, perhaps there is another way
>
to calculate UINT_MAX max power. Also use min_t as to make sure it's
>
uint type.
>
>
[1] UBSAN: shift-out-of-bounds in fs/ext4/mballoc.c:2713:24
>
shift exponent 60 is too large for 32-bit type 'int'
>
Call Trace:
>
__dump_stack lib/dump_stack.c:79 [inline]
>
dump_stack+0x137/0x1be lib/dump_stack.c:120
>
ubsan_epilogue lib/ubsan.c:148 [inline]
>
__ubsan_handle_shift_out_of_bounds+0x432/0x4d0 lib/ubsan.c:395
>
ext4_mb_init_backend fs/ext4/mballoc.c:2713 [inline]
>
ext4_mb_init+0x19bc/0x19f0 fs/ext4/mballoc.c:2898
>
ext4_fill_super+0xc2ec/0xfbe0 fs/ext4/super.c:4983
>
>
Reported-by: syzbot+a8b4b0c60155e87e9484@xxxxxxxxxxxxxxxxxxxxxxxxx
>
Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@xxxxxxxxx>
Looks good. Feel free to add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
>
---
>
v2: updated > 32 condition to >= 32
>
>
> > + if (sbi->s_es->s_log_groups_per_flex > 32) {
>
> ^^ >= 32?
>
>
>
> Otherwise the patch looks good.
>
>
>
>
Thanks! Updated to >= 32 condition.
>
---
>
fs/ext4/mballoc.c | 11 +++++++++--
>
1 file changed, 9 insertions(+), 2 deletions(-)
>
>
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
>
index 99bf091fee10..a02fadf4fc84 100644
>
--- a/fs/ext4/mballoc.c
>
+++ b/fs/ext4/mballoc.c
>
@@ -2709,8 +2709,15 @@ static int ext4_mb_init_backend(struct super_block *sb)
>
}
>
>
if (ext4_has_feature_flex_bg(sb)) {
>
- /* a single flex group is supposed to be read by a single IO */
>
- sbi->s_mb_prefetch = min(1 << sbi->s_es->s_log_groups_per_flex,
>
+ /* a single flex group is supposed to be read by a single IO.
>
+ * 2 ^ s_log_groups_per_flex != UINT_MAX as s_mb_prefetch is
>
+ * unsigned integer, so the maximum shift is 32.
>
+ */
>
+ if (sbi->s_es->s_log_groups_per_flex >= 32) {
>
+ ext4_msg(sb, KERN_ERR, "too many log groups per flexible block group");
>
+ goto err_freesgi;
>
+ }
>
+ sbi->s_mb_prefetch = min_t(uint, 1 << sbi->s_es->s_log_groups_per_flex,
>
BLK_MAX_SEGMENT_SIZE >> (sb->s_blocksize_bits - 9));
>
sbi->s_mb_prefetch *= 8; /* 8 prefetch IOs in flight at most */
>
} else {
>
--
>
2.25.1
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR