Message ID | 20210203134351.1697508-1-snovitoll@gmail.com |
---|---|
State | Superseded |
Headers | show |
Series | fs/ext4: fix integer overflow in s_log_groups_per_flex | expand |
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: syzbot+a8b4b0c60155e87e9484@syzkaller.appspotmail.com > Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com> > --- > 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 >
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 {
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@syzkaller.appspotmail.com Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com> --- fs/ext4/mballoc.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)