On 2/20/12 4:41 PM, Haogang Chen wrote: > In alloc_flex_gd(), when flexbg_size is large, kmalloc size would > overflow and flex_gd->groups would point to a buffer smaller than > expected, causing OOB accesses when it is used. > > Note that in ext4_resize_fs(), flexbg_size is calculated using > sbi->s_log_groups_per_flex, which is read from the disk and only bounded > to [1, 31]. The patch returns NULL for too large flexbg_size Hm this raises a few questions I think. On the one hand, making sure the kmalloc arg doesn't overflow here is certainly a good thing and probably the right thing to do in the short term. So I guess: Reviewed-by: Eric Sandeen <sandeen@xxxxxxxxxx> for that, to close the hole. But the types are a mess; alloc_flex_gd() takes an unsigned long; it's passed an int, and assigns to flex_gd->count, an ext4_group_t (which is an unsigned int). They should probably all be ext4_group_t for consistency. But that's not the worst of it... Doesn't this also mean that a valid s_log_groups_per_flex (i.e. 31) will fail in this resize code? That would be an unexpected outcome. 2^31 groups per flex is a little crazy, but still technically valid according to the limits in the code. So really, trying to allocate an array of all possible groups-per-flex in the resize code is probably a really bad idea to start with, and the resize code has got serious problems if kmalloc(UINT_MAX-1) is expected to work... -Eric > Signed-off-by: Haogang Chen <haogangchen@xxxxxxxxx> > --- > fs/ext4/resize.c | 2 ++ > 1 files changed, 2 insertions(+), 0 deletions(-) > > diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c > index f9d948f..8601f4b 100644 > --- a/fs/ext4/resize.c > +++ b/fs/ext4/resize.c > @@ -161,6 +161,8 @@ static struct ext4_new_flex_group_data *alloc_flex_gd(unsigned long flexbg_size) > if (flex_gd == NULL) > goto out3; > > + if (flexbg_size >= UINT_MAX / sizeof(struct ext4_new_flex_group_data)) > + goto out2; > flex_gd->count = flexbg_size; > > flex_gd->groups = kmalloc(sizeof(struct ext4_new_group_data) * -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
