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Howlett" , mhiramat@kernel.org, peterz@infradead.org, Jann Horn , syzbot , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com, vbabka@suse.cz Subject: Re: [syzbot] [mm?] general protection fault in find_mergeable_anon_vma Message-ID: <20241210150528.GA31266@redhat.com> References: <4d05caee-d900-42e5-84e1-448cc62435b2@lucifer.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 95A6120033 X-Stat-Signature: oshi179a5ykhdxyyjqzj8cdwfxgizocj X-Rspam-User: X-HE-Tag: 1733843154-44238 X-HE-Meta: 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 qpq2L9JW 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000057, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 12/09, Lorenzo Stoakes wrote: > > (As discussed on IRC) how about moving up the dup_mmap_sem lock one level, we > can put the mm before the rmap lookup in build_map_info() is able to find it, > which should avoid the whole issue? Not sure I fully understand the problem, but so far I see nothing wrong in this idea. However, > @@ -1692,9 +1690,11 @@ static struct mm_struct *dup_mm(struct task_struct *tsk, > if (!mm_init(mm, tsk, mm->user_ns)) > goto fail_nomem; > > + uprobe_start_dup_mmap(); > err = dup_mmap(mm, oldmm); > if (err) > goto free_pt; > + uprobe_end_dup_mmap(); If try_module_get(mm->binfmt->module)) fails after that, dup_mm() does "goto free_pt;" and in this case ... > @@ -1709,6 +1709,7 @@ static struct mm_struct *dup_mm(struct task_struct *tsk, > mm->binfmt = NULL; > mm_init_owner(mm, NULL); > mmput(mm); > + uprobe_end_dup_mmap(); ... we have the unbalanced uprobe_end_dup_mmap(). Also. Perhaps we can change dup_mmap() to set MMF_XXX before uprobe_end_dup_mmap(), fail_uprobe_end: + if (retval) + set_bit(mm->flags, MMF_XXX); uprobe_end_dup_mmap(); return retval; Then build_map_info() can check this flag. I guess we can reuse some of MMF_OOM_ bits? May be MMF_UNSTABLE... Oleg.