On Fri, Dec 06, 2024 at 10:29:39PM +0100, Jann Horn wrote: > On Fri, Dec 6, 2024 at 10:18 PM syzbot > <syzbot+91cf8da9401355f946c3@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: e70140ba0d2b Get rid of 'remove_new' relic from platform d.. > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=13300330580000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=50c7a61469ce77e7 > > dashboard link: https://syzkaller.appspot.com/bug?extid=91cf8da9401355f946c3 > > compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40 > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=124130df980000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10a280f8580000 > > > > Downloadable assets: > > disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-e70140ba.raw.xz > > vmlinux: https://storage.googleapis.com/syzbot-assets/91f313d8125b/vmlinux-e70140ba.xz > > kernel image: https://storage.googleapis.com/syzbot-assets/a9bdf286943a/bzImage-e70140ba.xz > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+91cf8da9401355f946c3@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > ================================================================== > > BUG: KASAN: slab-use-after-free in __mmap_complete mm/vma.c:2408 [inline] > > BUG: KASAN: slab-use-after-free in __mmap_region+0x1802/0x2cd0 mm/vma.c:2469 > > Read of size 8 at addr ffff8880403a6118 by task syz-executor239/5461 > > This looks like it was introduced by commit 5ac87a885aec ("mm: defer > second attempt at merge on mmap()"), which went into 6.13-rc1? From a > glance it seems like the "vma_merge_existing_range(&vmg)" in > __mmap_region() needs a "vma = " at the start of the line. Thanks so much for so quickly noticing this...!! Ugh you're right, what a mistake. This would fit the report completely too, as the existing VMA would be freed etc. etc. I'll write a test to trigger this path soon, writing mmap_region() unit tests is on my TODO list now they're in vma.c The line referenced seems to be to vm_stat_account(), which references vma->vm_flags which is in other words the first time we try to access the vma pointer, UAF... Patch incoming in one second.
