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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1qg4ng-008Bt2-TA; Tue, 12 Sep 2023 14:55:36 +0000 Date: Tue, 12 Sep 2023 15:55:36 +0100 From: Matthew Wilcox To: syzbot Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com, Suren Baghdasaryan Subject: Re: [syzbot] [mm?] kernel BUG in vma_replace_policy Message-ID: References: <000000000000f392a60604a65085@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: E36B04001E X-Rspam-User: X-Stat-Signature: rcq3eia8wje6fwghm89zotaudgeswnf1 X-Rspamd-Server: rspam03 X-HE-Tag: 1694530540-354731 X-HE-Meta: U2FsdGVkX18/mC3/fHgk+j3idLm37D98v5ErEDG+0Y095PsExhUbgR3BMtf79EEbY5kwsXYQDwWLcR8V1PEdODZfZ7lJQKrmAMrHSk/BXUF5vvYTaNXDzRxS0Heg+l4BVBQhZ2RHNKHAWmRRnn8M8fdpy+2wPd9OIjE8qFraP6rn3so8yy8kenS3Zjwb46ExmEU2vZoZWmwIW8SF8WMw+VBQ9tZ12psS1ivlNxAjQjqtIv+H6/1LdneVEN9419jj42ua7vsxrvpryfTrZ9Z7YEhR7Fm4lZmaatVJt6eNGw4ynDNz2e+ZY58Y1tAdBigA2WchM5GdVAuskElAlMouojWc47bUXl68tzpJTc5gemRTBCQc/myJ//ZoM1Znt+ipgFF9t8oct51bnzVSs8rvFPFUpEI3FitvjE7h6Hy06mQakRDusBPb7TaVRV20Cv7VPyS/7IjvsktSxu5V2ihMNQ0yvzIQdDsr30HVawJY7NODVZkps6lBCwtqO3bi57aKf4xvUDyqgYVgCIYba7UNQ5wjMkwGoPcemxxy1baqCY1oojV/ahiGU56Cgzhkg2A4B/qY546I1qq/22NAmI0MHB9TEtRjaGJh3SszqAaXLS/vjbxStqVKh/zO9V0rsKZmRbz+kIBeceQj/YCC9sX2dO/fV3hGKQ6sqVs6ycmT725lS5H2PbYe8rZ2sEBFKMK4HML4S19yJgXVJwOhz88sOfHW0kxnzcJHrC7m0YxRB6UL0TWbeOJUDgHmq2mE5nUha5wQWhjlKXzfsNOZuGlVNaXhxXjzkAtTqU8hrYMpEFbU8SWgJTend0KAY4yvUbzkW+tA/XQshDga7Gt1hBzY7RLqT9hDdNVjg/dWu+nYevI1TLzxJndXQmBgO/yW+fo/Gx22aUgvJ3O51771J5gGSxjJ7HZ8zrmDi0V7I9K1fIQK/ideLM53LiGetl6bVBg4xmCWI6pGnim/K7+VY1L vxXfN2aG 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Sep 12, 2023 at 06:30:46AM +0100, Matthew Wilcox wrote: > On Tue, Sep 05, 2023 at 06:03:49PM -0700, syzbot wrote: > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: a47fc304d2b6 Add linux-next specific files for 20230831 > > git tree: linux-next > > console+strace: https://syzkaller.appspot.com/x/log.txt?x=16502ddba80000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=6ecd2a74f20953b9 > > dashboard link: https://syzkaller.appspot.com/bug?extid=b591856e0f0139f83023 > > compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40 > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=120e7d70680000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1523f9c0680000 > > > > Downloadable assets: > > disk image: https://storage.googleapis.com/syzbot-assets/b2e8f4217527/disk-a47fc304.raw.xz > > vmlinux: https://storage.googleapis.com/syzbot-assets/ed6cdcc09339/vmlinux-a47fc304.xz > > kernel image: https://storage.googleapis.com/syzbot-assets/bd9b2475bf5a/bzImage-a47fc304.xz > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+b591856e0f0139f83023@syzkaller.appspotmail.com > > #syz test > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > index 42b5567e3773..90ad5fe60824 100644 > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -1342,6 +1342,7 @@ static long do_mbind(unsigned long start, unsigned long len, > vma_iter_init(&vmi, mm, start); > prev = vma_prev(&vmi); > for_each_vma_range(vmi, vma, end) { > + vma_start_write(vma); > err = mbind_range(&vmi, vma, &prev, start, end, new); > if (err) > break; Suren, can you take a look at this? The VMA should be locked by the call to queue_pages_range(), but by the time we get to here, the VMA isn't locked. I don't see anywhere that we cycle the mmap_lock (which would unlock the VMA), but I could have missed something. The two VMA walks should walk over the same set of VMAs. Certainly the VMA being dumped should have been locked by the pagewalk: vma ffff888077381a00 start 0000000020c2a000 end 0000000021000000 mm ffff8880258a8980 prot 25 anon_vma 0000000000000000 vm_ops 0000000000000000 pgoff 20c2a file 0000000000000000 private_data 0000000000000000 flags: 0x8100077(read|write|exec|mayread|maywrite|mayexec|account|softdirty) syscall(__NR_mbind, /*addr=*/0x20400000ul, /*len=*/0xc00000ul, /*mode=*/4ul, /*nodemask=*/0ul, /*maxnode=*/0ul, /*flags=*/3ul); 20400000 + c00000 should overlap 20c2a000-21000000