2021-02-03 13:47:03

by Sabyrzhan Tasbolatov

[permalink] [raw]
Subject: [PATCH] fs/ext4: fix integer overflow in s_log_groups_per_flex

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: [email protected]
Signed-off-by: Sabyrzhan Tasbolatov <[email protected]>
---
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..e1e7ffbba1a6 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


2021-02-23 17:06:29

by Jan Kara

[permalink] [raw]
Subject: Re: [PATCH] fs/ext4: fix integer overflow in s_log_groups_per_flex

On Wed 03-02-21 19:43:51, 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: [email protected]
> Signed-off-by: Sabyrzhan Tasbolatov <[email protected]>
> ---
> 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..e1e7ffbba1a6 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) {
^^ >= 32?

Otherwise the patch looks good.

Honza


> + 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 <[email protected]>
SUSE Labs, CR

2021-02-24 10:02:38

by Sabyrzhan Tasbolatov

[permalink] [raw]
Subject: [PATCH v2] fs/ext4: fix integer overflow in s_log_groups_per_flex

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: [email protected]
Signed-off-by: Sabyrzhan Tasbolatov <[email protected]>
---
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