Apologies for sending multiple copies of same email. There was some issue on my side. On 9/11/23 2:40 PM, Muhammad Usama Anjum wrote: > Syzbot has hit the following bug on current and all older kernels: > BUG: KASAN: out-of-bounds in ext4_ext_rm_leaf fs/ext4/extents.c:2736 [inline] > BUG: KASAN: out-of-bounds in ext4_ext_remove_space+0x2482/0x4d90 fs/ext4/extents.c:2958 > Read of size 18446744073709551508 at addr ffff888073aea078 by task syz-executor420/6443 > > On investigation, I've found that eh->eh_entries is zero, ex is > referring to last entry and EXT_LAST_EXTENT(eh) is referring to first. > Hence EXT_LAST_EXTENT(eh) - ex becomes negative and causes the wrong > buffer read. > > element: FFFF8882F8F0D06C <----- ex > element: FFFF8882F8F0D060 > element: FFFF8882F8F0D054 > element: FFFF8882F8F0D048 > element: FFFF8882F8F0D03C > element: FFFF8882F8F0D030 > element: FFFF8882F8F0D024 > element: FFFF8882F8F0D018 > element: FFFF8882F8F0D00C <------ EXT_FIRST_EXTENT(eh) > header: FFFF8882F8F0D000 <------ EXT_LAST_EXTENT(eh) and eh > > Cc: stable@xxxxxxxxxxxxxxx > Reported-by: syzbot+6e5f2db05775244c73b7@xxxxxxxxxxxxxxxxxxxxxxxxx > Closes: https://groups.google.com/g/syzkaller-bugs/c/G6zS-LKgDW0/m/63MgF6V7BAAJ > Fixes: d583fb87a3ff ("ext4: punch out extents") > Signed-off-by: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx> > --- > This patch is only fixing the local issue. There may be bigger bug. Why > is ex set to last entry if the eh->eh_entries is 0. If any ext4 > developer want to look at the bug, please don't hesitate. > --- > fs/ext4/extents.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c > index e4115d338f101..7b7779b4cb87f 100644 > --- a/fs/ext4/extents.c > +++ b/fs/ext4/extents.c > @@ -2726,7 +2726,7 @@ ext4_ext_rm_leaf(handle_t *handle, struct inode *inode, > * If the extent was completely released, > * we need to remove it from the leaf > */ > - if (num == 0) { > + if (num == 0 && eh->eh_entries) { > if (end != EXT_MAX_BLOCKS - 1) { > /* > * For hole punching, we need to scoot all the -- BR, Muhammad Usama Anjum
