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Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1vK0f2-00000009u54-04RV; Fri, 14 Nov 2025 20:44:48 +0000 Date: Fri, 14 Nov 2025 20:44:47 +0000 From: Matthew Wilcox To: ssrane_b23@ee.vjti.ac.in Cc: akpm@linux-foundation.org, shakeel.butt@linux.dev, eddyz87@gmail.com, andrii@kernel.org, ast@kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kernel-mentees@lists.linux.dev, skhan@linuxfoundation.org, david.hunter.linux@gmail.com, khalid@kernel.org, syzbot+09b7d050e4806540153d@syzkaller.appspotmail.com Subject: Re: [PATCH] mm/filemap: fix NULL pointer dereference in do_read_cache_folio() Message-ID: References: <20251114193729.251892-1-ssranevjti@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251114193729.251892-1-ssranevjti@gmail.com> X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: C654C40014 X-Stat-Signature: ixb88i5qtgi1sxydiwmsafkjhg8skhz7 X-Rspam-User: X-HE-Tag: 1763153092-616453 X-HE-Meta: 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 ikmGi2Il vGGypWq9HPgdibNrC0v+nwQ963EtJ0lWdAxcHB386v449gU+Fg/QJN6wL4RIHGMdPiIi1eMTuM2bq3sMhaVFUgPZ6XtdL3UnWKwIUey8QrQiieZDQ6ToWBEN5Ycdez/qd7E1XlqmP0wm/9GP7dB3XGnKQOL9SSf8wVCzeXb/9pTUBCO+CcfDsi3OV9GbJwha5NkRzOZebi5oWsP1r61T3QhZyOFBTSPaRAiDyibExk2oVjIx9D1CMXip48v65hr8pKXulbyPIl6g2RXx8BnKBGIfWr3gwGCCXISTVTrisksLT67yPbQvPTGo70fWJcXhC7pBOLiyJ0om660lTRCGmNxt+MF2PiiMYovQpoVUFwmgPQJ6vN1o3vAGJbxQk2hJk2TnPOyA7Rjn5kbc= 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: List-Subscribe: List-Unsubscribe: On Sat, Nov 15, 2025 at 01:07:29AM +0530, ssrane_b23@ee.vjti.ac.in wrote: > When read_cache_folio() is called with a NULL filler function on a > mapping that does not implement read_folio, a NULL pointer > dereference occurs in filemap_read_folio(). > > The crash occurs when: > > build_id_parse() is called on a VMA backed by a file from a > filesystem that does not implement ->read_folio() (e.g. procfs, > sysfs, or other virtual filesystems). Not a fan of this approach, to be honest. This should be caught at a higher level. In __build_id_parse(), there's already a check: /* only works for page backed storage */ if (!vma->vm_file) return -EINVAL; which is funny because the comment is correct, but the code is not. I suspect the right answer is to add right after it: + if (vma->vm_file->f_mapping->a_ops == &empty_aops) + return -EINVAL; Want to test that out?